| 1. |
- Camacho, W., et al.
(författare)
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Assessment of thermal and thermo-oxidative stability of multiextruded recycled PP, HDPE and a blend thereof
- 2002
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 78:2, s. 385-391
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Tidskriftsartikel (refereegranskat)abstract
- Differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA) and chemiluminescence (CL) techniques have been used for assessment of thermal and thermo-oxidative stability of recycled PP, HDPE and their blend containing 20 wt.% of PP. The pure polymers and the blend were subjected to six extrusion cycles. The oxidation induction time (OIT) of the PP, PE and the blend decreased with the number of extrusion cycles also did the temperature of oxidation (T-ox). The thermal stability of PE decreased with the number of number of processing cycles, which may indicate that the shear forces during processing induce chain scission of the polymer backbone leading mainly to shortening of the chains. PP, however showed a decrease in thermal stability up to the third extrusion, and about the same stability during further processing. Thus chain scission predominated during all the extrusions and no chain branching or crosslinking were observed. The behaviour of the blend showed a synergetic tendency and did not obey the mixture rule. The CL runs produced a clearer picture of the oxidation process in blends since two peaks were observed, a sharp one corresponding to the PP and the other of bimodal shape to PE. The PP appeared to oxidize first and accelerated the oxidation of PE due to the presence of oxidation sites in the PE-PP interfaces. The blend of PP an HDPE mechanically mixed appeared to be a two-phase system in the molten state. This information can not be obtained from DSC and TG experiments.
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| 2. |
- Fateh-Alavi, K., et al.
(författare)
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The effect of antioxidants on the surface oxidation and surface cracking of crosslinked polydimethylsiloxane
- 2001
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 74:1, s. 49-57
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Tidskriftsartikel (refereegranskat)abstract
- Crosslinked polydimethylsiloxanes with three different chain-breaking antioxidants (Irganox 1076, Irganox 565 and Tinuvin 770) were exposed to air plasma (GHz), and the surface structures of the exposed samples were assessed by contact angle measurements, X-ray photoelectron spectroscopy, optical and scanning electron microscopy, and surface profilometry before and after uniaxial stretching. It was found that samples containing antioxidants oxidized more slowly than the reference sample with no antioxidant. Higher doses of air plasma were required to form a brittle silica-like layer in the samples with antioxidant than in the reference sample with no antioxidant. Tinuvin 770 showed the strongest antioxidative effect whereas Irganox 1076 and Irganox 565 were similar in efficiency.
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| 3. |
- Fateh-Alavi, K., et al.
(författare)
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The effect of stabilizer concentration on the air-plasma-induced surface oxidation of crosslinked polydimethylsiloxane
- 2002
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 78:1, s. 17-25
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of three stabilizers-a hindered phenol (Irganox 1076), a hindered amine light stabilizer (Tinuvin 770) and a bifunctional stabilizer with chain-breaking hindered phenol and secondary amine and hydroperoxide-decomposing sulphide moieties (Irganox 565)-in crosslinked polydimethylsiloxane were varied using swelling solutions of the stabilizers at different concentrations. The concentration of the stabilizer in the rubber was assessed by UV-Vis spectroscopy of Soxhlet and microwave assisted extracts. Irganox 1076 and Tinuvin 770 were soluble in polydimethylsiloxane to at least 0.2-0.3 wt.%, whereas the solubility of Irganox 565 was considerably lower. The samples were exposed to GHz air plasma and the surface structures of the exposed samples were studied by X-ray photoelectron spectroscopy, and by optical and scanning electron microscopy after uniaxial stretching. The plasma exposure time required for the formation of an oxidised glassy layer increased in a linear fashion with increasing stabilizer concentration, suggesting that the consumption rate was constant in time during the plasma exposure. Tinuvin 770 showed the strongest overall protecting effect whereas Irganox 565 showed the strongest protecting effect per mass fraction of stabilizer. Irganox 1076 was of moderate efficiency. The results suggest that efficient protection towards air plasma is achieved with hindered amine stabilizers or with stabilizers combining chain-breaking and hydroperoxide-decomposing functions. Differential scanning calorimetry showed that Tinuvin 770 and Irganox 565 protected polydimethylsiloxane against thermal oxidation at elevated temperatures. The chemical consumption of these stabilizers followed basically the classical scheme with zero-order kinetics and a rate constant obeying the Arrhenius law.
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| 4. |
- Gallet, G., et al.
(författare)
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Thermal oxidation of poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer : focus on low molecular weight degradation products
- 2002
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 77:1, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- The oxidative thermal degradation of poloxamer 407, a poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, at 50 and 80 degreesC in air was studied by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS). At 80 degreesC, we found that degradation was initiated on the PPO block of the copolymer by three mechanisms involving hydroperoxyl formation and depropagation. 1,2-propanediol,1-acetate; 1,2-propanediol,2-formate; 1, 2-propanediol,1-acetate, 2-formate and 2-propanone,1-hydroxy were the first degradation products produced. Random chain scissions and a sharp decrease in the molecular weight of the material followed the initiation period. Formic acid and acetic acid, formed upon degradation, participated in esterification reactions leading to the formation of the formate and acetate forms of 1,2-propanediol and ethanediol. Though degradation at 50 degreesC was much slower, the oxidative mechanisms leading to low molecular weight formates and acetates were the same as those observed at 80 degreesC.
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| 5. |
- Haider, N., et al.
(författare)
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Loss of Chimassorb 944 from LDPE and identification of additive degradation products after exposure to water, air and compost
- 2001
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 74:1, s. 103-112
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Tidskriftsartikel (refereegranskat)abstract
- A low-density polyethylene (LDPE) film containing a hindered amine light stabiliser (Chimassorb 944) was exposed to a composting mixture, chemical hydrolysis at pH 5 and pH 7 and air, in all cases at room temperature and for a period of 4 years. The structural changes of the LDPE film were investigated by differential scanning calorimetry (DSC) and size exclusion chromatography with viscosity detection (SEC-viscosity) while degradation products of LDPE and Chimassorb 944 were identified by gas chromatography-mass spectrometry (GC-MS). Determination of the amount of remaining stabiliser was performed using an ultrasonic extraction technique followed by LN spectroscopy analysis (250 nm, absorption of 1,3,5-triazine group). The ultrasonic extraction of Chimassorb 944 was carried out at 60 degreesC for a period of 1 h, using chloroform as extracting solvent. Loss of the stabiliser accompanied by structural changes of the polymeric matrix occurred during exposition time and was strongly influenced by exposure conditions. Thus, the fastest loss of the stabiliser was found on exposition to chemical hydrolysis at both pH while the slowest loss was observed during ageing in compost. Different products formed from Chimassorb 944 were found in all the tested environments as a result both of degradation of the stabiliser to smaller fragments and of reactions between these fragments and other additives present in LDPE. Thus, (Z)-9-octadecenamide was found in both unexposed and all the tested samples and was formed already during processing. 2,2,6,6-Tetramethyl-4-aminopiperidine was found in air and compost aged samples while 2,4-di-t-butyl-6-nitro-phenol was found in the samples exposed to air and water environments and [2-cyclohexene-1-dione, 3,5-dimethyl, O-methyloxime] were found exclusively in the samples aged in water at pH 5.
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| 6. |
- Hakkarainen, Minna
(författare)
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New PVC materials for medical applications - the release profile of PVC/polycaprolactone-polycarbonate aged in aqueous environments
- 2003
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 80:3, s. 451-458
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Tidskriftsartikel (refereegranskat)abstract
- Medical grade PVC plasticised with polycaprolactone-polycarbonate (PCL-PC) was subjected to aqueous environments at different temperatures. The release profile during ageing was determined by solid phase microextraction (SPME) and GC-MS. At the same time changes in the surface composition due to, for example, migration of PCL-PC from the blend were followed by FTIR. Almost no changes in the material or its surface composition were observed during 98 days at 37 degreesC in water or phosphate buffer. Only trace amount of 6-hydroxyhexanoic acid the final hydrolysis product of PCL-PC was detected in the GC-MS chromatograms and the weight loss was negligible. Even when the ageing temperature was raised to 70 degreesC only minor increase in the amount of 6-hydroxyhexanoic acid was observed and the weight loss after 98 days was under 1%. Changes in the FTIR spectra indicating migration of PCL-PC towards the surface of the PVC/PCL-PC tubing were observed first after 70 days at 70 degreesC. Large increase in the hydrolysis rate of PCL-PC and almost complete depletion of PCL-PC from the blend was observed when the ageing temperature was raised to 100 degreesC.
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| 7. |
- Mathew, Aji P., et al.
(författare)
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Studies on the thermal stability of natural rubber/polystyrene interpenetrating polymer networks : thermogravimetric analysis
- 2001
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 72:3, s. 423-439
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Tidskriftsartikel (refereegranskat)abstract
- The thermal degradation of natural rubber/polystyrene (NR/PS) interpenetrating polymer networks (IPNs) was studied and the effects of blend ratio, crosslink level and initiating system were analysed. The thermogravimetric analysis (TGA) shows that the IPNs are more stable than the pure components. The full-IPNs have better stability than semi-IPNs which is due to higher entanglement density of full-IPNs. The initial decomposition temperature and temperature for 50% decomposition (T50) increase with increase in concentration and crosslinker level of the plastic phase. The kinetics of degradation were analysed using nine mechanistic equations. The kinetic parameters such as activation energy, Arrhenius parameter and entropy of activation were determined. Thermal ageing studies of the samples were also conducted. The IPNs aged for 72 h at 100°C showed enhanced mechanical strength due to crosslinking on post curing.
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| 8. |
- Shanks, David, et al.
(författare)
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Improved Antioxidant Formulations for Polymeric Materials : Synergistic Protective Effects in Combinations of Organotellurium Compounds with Conventional Phenolic Antioxidants or Thiols
- 2003
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 81:2, s. 261-271
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Tidskriftsartikel (refereegranskat)abstract
- As judged by differential scanning calorimetry experiments at 190 °C and chemiluminescence measurements at 150 °C, addition of 0.10–0.30 wt.% of certain organotellurium compounds to polypropylene caused a notable protection against oxidation of the material. The best stabilizers (diaryl telluride 3 and alkyl aryl telluride 4), offered a similar degree of protection as commercial stabilizer formulations comprising a mixture of Irganox® 1010 and Irgafos® 168 (0.1 wt.% of each). The protective effect of the organotelluriums was substantially improved in combinations with sterically hindered phenols or thiols. The protection was often much better than the added effects of the individual components and, thus, can be considered as synergistic. Evaluation of a series of stabilizers where tellurium had been exchanged for selenium and sulfur (compounds 2) showed that the synergistic protective effect was unique for tellurium.
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| 9. |
- Wallström, Stina, et al.
(författare)
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Development and comparison of test methods for evaluating formation of biofilms on silicones
- 2002
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 78:2, s. 257-262
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Tidskriftsartikel (refereegranskat)abstract
- Silicone rubber formulations used for outdoor high voltage insulation are sometimes reported to be colonized by microorganisms. Different formulations show different sensitivity towards biological growth. In this study five rubbers were tested. Two standard practices were used, ASTM G21-90 and IEC 68-2-10. In addition a new method was developed to measure the rate of colonisation of a sample by biological growth. Results showed that the tested rubbers supported fungal growth when an external carbon source was available. Thus none of the silicones can be called bio-resistant. However the materials are not biodegradable either. This was clearly shown when mould spores were added to the samples in clean water, when none of the rubbers was contaminated. Some of the materials did, however, support growth when only nutrient salts, no carbon source, was added. The most bioresistant formulations contained the flame retardant zinc borate, indicating that this additive suppresses fungal growth. Further investigation with the new method supported that theory.
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| 10. |
- Westphal, C., et al.
(författare)
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Py-GC/MS as a means to predict degree of degradation by giving microstructural changes modelled on LDPE and PLA
- 2001
-
Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 73:2, s. 281-287
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Tidskriftsartikel (refereegranskat)abstract
- The degree of changes in the patterns and ratio of peaks (oligomers) in pyrograms from pyrolysed polymers exposed to hydrolysis (chemical and/or biological) and oxidation are related the extent of degradation and could be used to predict life-time. PLA and LDPE with enhanced degradability (LDPE with LLDPE, corn starch and pro-oxidant [SBS + manganese stearate (MB)] were used as models for hydrolysable and oxidisable polymers and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) analysed for its versatility show differences in microstructure of polymers. In parallel size exclusion chromatography (SEC), gas chromatography mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR) gave other signs of degradation. Pyrolysed LDPE samples gave fragments constituting a triplet from C-6, to C-30, With a peak maxima at C-10, C-14 and C-18 expect for LDPE with pro-oxidant and starch exposed to thermo-oxidation. This sample instead had a high amount of C-9 fragment which is related to hydrogen abstraction occuring along the chain. FTIR showed that this samples had formed higher amounts of carbonyl compounds at the surface. Thermogravimetry analysis (TGA) gave changes in the constituents of the LDPE with starch, pro-oxidant and starch. By fractionated Py-GC-MS at 400 and 500 degreesC, acetaldehyde, acrylic acid, lactoyl acrylic acid, two lactide isomers and cyclic oligomers up to pentamer were identified in poly(lactide) (PLA). The ratio of meso-lactide to D, L-lactide was lower in the biotically hydrolysed PLA, while the PLA matrices changes of unaged and chemically hydrolysed samples gave quite similar pyrograms. Thus, the most severly thermo-oxidised LDPE-sample had in a large peak at the C-9 fragment opposite to the other LDPE-samples while the most severly hydrolysed PLA (biotically hydrolysed) had a ratio of meso-lactide to D,L-lactide quite different from unaged and chemically hydrolysed sample.
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| 11. |
- Ahlinder, Astrid, et al.
(författare)
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Minimise thermo-mechanical batch variations when processing medical grade lactide based copolymers in additive manufacturing
- 2020
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 181
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Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing is suitable for producing complex geometries; however, variation in thermo-mechanical properties are observed during one batch cycle when degradable aliphatic polyesters of medical grade are used in melt extrusion-based methods. This is one important reason for why additive manufacturing has not yet been fully utilised to produce degradable medical implants. Herein, the internal variation has been minimised during one batch cycle by assessing the effect of different processing parameters when using commercially available medical grade copolymers. To minimise the molar mass, thermal and mechanical variation within one batch cycle, the rheological fingerprint of the commercially available medical grade poly(L-lactide-co-ε-caprolactone) and poly(L-lactide-co-trimethylene carbonate) has been correlated to the process parameters of the ARBURG Plastic Freeforming. An increase in the temperature up to 220°C and the associated increase in pressure are beneficial for the viscoelastic and thermally stable poly(L-lactide-co-ε-caprolactone). In contrast, a temperature below 220°C should be used for the poly(L-lactide-co-trimethylene carbonate) to reduce the variation in strain at break during one batch cycle. The residence time is decreased through the increase of the discharge parameter. An increase in temperature is however required to reduce the viscosity of the polymer and allow the pressure to stay within the machine limitations at higher discharge parameters. The results are highly relevant to the development of additive manufacturing for the production of degradable medical devices with identical properties. In fact, Food and Drug Administration guidelines for additive manufacturing of medical implants specify the need to control changes in material properties during the process.
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| 12. |
- Akhlaghi, Shahin, et al.
(författare)
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Degradation of carbon-black-filled acrylonitrile butadiene rubber in alternative fuels : Transesterified and hydrotreated vegetable oils
- 2016
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 123, s. 69-79
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Tidskriftsartikel (refereegranskat)abstract
- The deterioration of acrylonitrile butadiene rubber (NBR), a common sealing material in automobile fuel systems, when exposed to rapeseed biodiesel and hydrotreated vegetable oil (HVO) was studied. The fuel sorption was hindered in HVO-exposed rubber by the steric constraints of bulky HVO molecules, but it was promoted in biodiesel-exposed rubber by fuel-driven cavitation in the NBR and by the increase in diffusivity of biodiesel after oxidation. The absence of a tan δ peak of the bound rubber and the appearance of carbon black particles devoid of rubber suggested that the cavitation was made possible in biodiesel-aged rubber by the detachment of bound rubber from particle surfaces. The HVO-exposed NBR showed a small decrease in strain-at-break due to the migration of plasticizer from the rubber, and a small increase in the Young’s modulus due to oxidative crosslinking. A drastic decrease in extensibility and Payne-effect amplitude of NBR on exposure to biodiesel was explained as being due to the damage caused by biodiesel to the continuous network of bound rubber-carbon black. A decrease in the ZnO crystal size with increasing exposure time suggested that the particles are gradually dissolved in the acidic components of oxidized biodiesel. The Zn2+ cations released from the dissolution of ZnO particles in biodiesel promoted the hydrolysis of the nitrile groups of NBR.
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| 13. |
- Akhlaghi, Shahin, et al.
(författare)
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Degradation of fluoroelastomers in rapeseed biodiesel at different oxygen concentrations
- 2017
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 136, s. 10-19
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of fluoroelastomers (FKM) based on different monomers, additives and curing systems was studied after exposure to rapeseed biodiesel at 100 °C and different oxygen partial pressures. The sorption of fuel in the carbon black-filled FKM terpolymer was promoted by the fuel-driven cavitation in the rubber. The bisphenol-cured rubbers swelled more in biodiesel than the peroxide-cured FKM, presumably due to the chain cleavage caused by the attack of biodiesel on the double bonds formed during the bisphenol curing. With any of the selected types of monomer, the FKM rubbers absorbed biodiesel faster and to a greater extent with increasing oxygen partial pressure due to the increase in concentration of the oxidation products of biodiesel. Water-assisted complexation of biodiesel on magnesium oxide and calcium hydroxide particles led to dehydrofluorination of FKM, resulting in an extensive fuel uptake and a decrease in the strain-at-break and the Young's modulus of the rubbers. An increase in the CH2-concentration determined by infrared spectroscopy, and the appearance of biodiesel flakes in scanning electron micrographs of the extracted rubbers, were explained as being due to the presence of insoluble biodiesel grafted onto FKM on the unsaturated sites resulting from dehydrofluorination. The extensibility of the GFLT-type FKM was the least affected on exposure to biodiesel because this rubber contained less unsaturation and metal oxide/hydroxide particles.
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| 14. |
- Akhlaghi, Shahin, et al.
(författare)
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Deterioration of acrylonitrile butadiene rubber in rapeseed biodiesel
- 2015
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 111, s. 211-222
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Tidskriftsartikel (refereegranskat)abstract
- The deterioration of acrylonitrile butadiene rubber (NBR) exposed to rapeseed biodiesel at 90 degrees C was studied. The oxidation of biodiesel and NBR during ageing was monitored by H-1 NMR and infrared spectroscopy, HPLC and titration methods. The oxidation of biodiesel was impeded in the presence of NBR, but promoted in biodiesel-exposed rubber. This was explained as being due to the migration of stabilizer from the rubber to biodiesel, the diffusion of dissolved oxygen from biodiesel into NBR and the absorption of oxidation precursors of biodiesel by the rubber. The resemblance between the anomalous sorption kinetics of biodiesel in NBR and the equilibrium benzene uptake by the aged rubbers revealed that biodiesel caused a network defect in NBR, resulting in a gradual increase in the equilibrium swelling. The cleavage of crosslinks was implausible since the Young's modulus of the rubber at low strains, disregarding an initial decrease, increased with increasing exposure time. The appearance of 'naked' carbon black particles in the scanning electron micrographs of the aged rubbers and a drastic decrease in the strain-at-break of NBR after exposure to biodiesel suggests that internal cavitation was caused by the attack of biodiesel on the acrylonitrile units of NBR.
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| 15. |
- Akhlaghi, Shahin, et al.
(författare)
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Effects of ageing conditions on degradation of acrylonitrile butadiene rubber filled with heat-treated ZnO star-shaped particles in rapeseed biodiesel
- 2017
-
Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321.
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Tidskriftsartikel (refereegranskat)abstract
- The degradation of acrylonitrile butadiene rubber (NBR) after exposure to biodiesel at different oxygen partial pressures in an automated ageing equipment at 80 °C, and in a high-pressure autoclave at 150 °C was studied. The oxidation of biodiesel was promoted by an increase in oxygen concentration, resulting in a larger uptake of fuel in the rubber due to internal cavitation, a greater decrease in the strain-at-break of NBR due to the coalescence of cavity, and a faster increase in the crosslinking density and carbonyl index due to the promotion of the oxidation of NBR. During the high-temperature autoclave ageing, less fuel was absorbed in the rubber, because the formation of hydroperoxides and acids was impeded. The extensibility of NBR aged in the autoclave decreased only slightly due to the cleavage of rubber chains by the biodiesel attack. The degradation of NBR in the absence of carbon black was explained as being due to oxidative crosslinking. The dissolution of ZnO crystals in the acidic components of biodiesel was retarded by removing the inter-particle porosity and surface defects through heat treating star-shaped ZnO particles. The rubber containing heat-treated ZnO particles swelled less in biodiesel than a NBR filled with commercial ZnO nanoparticles, and showed a smaller decrease in the strain-at-break and less oxidative crosslinking.
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| 16. |
- Albertsson, A-C., et al.
(författare)
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Environment-adaptable polymers
- 1993
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 41:3, s. 345-349
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Tidskriftsartikel (refereegranskat)
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| 17. |
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| 18. |
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| 19. |
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| 20. |
- Alin, Jonas, et al.
(författare)
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Migration from polycarbonate packaging to food simulants during microwave heating
- 2012
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Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:8, s. 1387-1395
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between polycarbonate (PC) packaging and different food simulants during microwave heating were evaluated by identifying the compounds migrating into aqueous, alcoholic and fatty food simulants. The migration of compounds, such as 9,9-dimethylxanthene and m-tert-butyl-phenol, from the PC package to ethanol and isooctane increased significantly during microwave heating as compared to conventional heating. The increase in migration can be explained by degradation caused by microwave heating and/or stronger food simulant interactions. Depending on the food simulant the migrants were quantified either by multiple headspace–solid-phase micro-extraction (MHS-SPME) or direct injection in combination with gas chromatography-mass spectrometry. A partial least squares (PLS) regression model was developed to predict the extraction efficiency for headspace–solid-phase micro-extraction (HS-SPME) of food package migrants from the analyte properties. The most significant property for prediction of the enrichment factors was the octanol-water partition coefficient (log Kow). Polydimethylsiloxane (PDMS) and polydimethylsiloxane/divinylbenzene (PDMS/DVB) fibers were compared for the extraction of the migrants. High correlation was found between the PDMS and PDMS/DVB enrichment factors (R2=0.98), but the extraction by PDMS/DVB fiber was much more efficient compared to the extraction by PDMS fiber. The detection limits after SPME extraction by PDMS/DVB fiber were 1, 0.1 and 3 ng/L for 4-ethoxy-ethyl-benzoate, 2,4-di-tert-butyl-phenol and benzophenone, respectively.
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| 21. |
- Alongi, Jenny, et al.
(författare)
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Superior flame retardancy of cotton by synergetic effect of cellulose-derived nano-graphene oxide carbon dots and disulphide-containing polyamidoamines
- 2019
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- Linear polyamidoamines containing disulphide groups (SS-PAAs) were prepared by polyaddition of L-cystine with 2,2-bisacrylamidoacetic acid (B-CYSS), N,N'-methylenebisacrylamide (M-CYSS) and 1,4-bisacryloylpiperazine (BP-CYSS). They were evaluated as flame retardants for cotton, alone or with cellulose-derived nano-graphene oxide (nGO) carbon dots, to assess whether, due to their potential as radical scavengers, the latter would improve the already good performance of SS-PAAs. In vertical flame spread tests (VEST), cotton treated with 1% nGO burned as quickly as cotton, whereas B-CYSS, M-CYSS and BP-CYSS extinguished the flame at add-ons >= 12, 16 and 20%, respectively. Probably, the gaseous products of SS-PAA thermal degradation quenched the radicals involved in oxidation. Cotton treated with 8,12 and 15%, respectively, of B-CYSS, M-CYSS and BP-CYSS burned completely, but further addition of 1% nGO either inhibited ignition or shortly extinguished the flame, demonstrating synergism between the two components. Synergism was confirmed by assessing the synergism effectiveness parameter for the residual mass fraction (RMF) and by comparing the calculated and experimental TG curves in air for the cotton/SS-PAA-nGO systems. In cone calorimetry tests, the presence of nGO did not improve the already good performances of SS-PAAs, supporting the hypothesis that the action of both takes place in the gas phase.
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| 22. |
- Altgen, Michael, et al.
(författare)
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Hydroxyl accessibility and dimensional changes of Scots pine sapwood affected by alterations in the cell wall ultrastructure during heattreatment
- 2018
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 152, s. 244-252
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Tidskriftsartikel (refereegranskat)abstract
- There is a complex link between the water sorption behavior and the presence of accessible hydroxyl groups in the wood cell wall, which can be altered by heat-treatment (HT). This study analyses the effect of changes in the cell wall ultrastructure caused by two HT techniques on the hydroxyl accessibility, water vapor sorption and dimensional changes of Scots pine (Pinus sylvestris L.) sapwood. HT of wood in pressurized hot water at 120-170 °C was applied to cause the preferential bond cleavage, whereas HT of wood in oven-dry state in superheated steam at 180-240 °C was performed to create additional covalent cross-links within the cell wall matrix. Removal of cell wall polymers by HT and water leaching reduced the oven-dry dimensions of wood and enhanced the cellulose aggregation during drying. Cellulose aggregation restricted the cell wall shrinkage in circumferential direction, resulting in inhomogeneous shrinkage of the cell wall with only little changes in lumen volume by HT. Cellulose aggregation also reduced the water-saturated dimensions, but a decrease in swelling was only achieved when additional cross-links were formed by HT in dry state. Additional cross-links in the cell wall matrix also resulted in an additional reduction in water sorption at 25 °C and 93% RH. However, this was not caused by a further reduction in the hydroxyl accessibility. Instead, cross-linking was shown to reduce the amount of accessible OH groups that are simultaneously active in sorption, which was explained based on the concept of sorption of water dimers at hydroxyl group pairs at high RH levels.
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| 23. |
- Anderberg, Anders, et al.
(författare)
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Degradation of floor adhesives as a function of pH
- 2008
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Ingår i: Polymer Degradation and Stability. - : Elsevier BV. - 1873-2321 .- 0141-3910. ; 93:2, s. 329-334
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Tidskriftsartikel (refereegranskat)abstract
- Floor adhesives on cement-based substrates may degrade if the pH is high enough and this has in many cases led to emissions of odorous substances and deteriorated indoor air quality. We have used isothermal calorimetry to assess the degradation rate of two floor adhesives as a function of pH. The rate of heat production measured by the calorimeter is proportional to the reaction rate. The degradation rate was similar for a ''standard'' and a ''low emitting'' adhesive, but the low emitting adhesive did not release volatile reaction products. The results show that adhesive degradation is strongly pH dependent. A model of alkaline hydrolysis based on two reaction sites is discussed.
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| 24. |
- Arias, Veluska, et al.
(författare)
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Forecasting linear aliphatic copolyester degradation through modular block design
- 2016
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Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 130, s. 58-67
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Tidskriftsartikel (refereegranskat)abstract
- The development of efficient methods to predict the degradation of renewable polymeric materials is continuously sought in the field of polymer science. Herein, we present a modular build-up approach to create polyester-based materials with forecasted degradation rates based on the hydrolysis of the constituent polymer blocks. This involved the strategic combination of critical factors affecting polyester hydrolysis, i.e. hydrophobicity and degree of crystallinity. The starting point of this method was a toolbox of polymers with different hydrophobicities and degrees of crystallinity, as well as an understanding of their inherent differences in hydrolysis rate. Knowledge of the hydrolysis of each polymer block module enabled the prediction of the overall degradation behavior of the constructed copolymers. Taking advantage of the primary factors that affect polymer degradation, block copolymers could be independently designed to incorporate soft or rigid and faster or slower degradation properties. This approach generated a shift for how molecular design can be used to predict the degradation behavior of intended materials for different applications.
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| 25. |
- Azwar, Edwin, et al.
(författare)
-
Pyrolysis-GC-MS reveals important differences in hydrolytic degradation process of wood flour and rice bran filled polylactide composites
- 2012
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:3, s. 281-287
-
Tidskriftsartikel (refereegranskat)abstract
- Pyrolysis-GC-MS of polylactide (PLA) biocomposites before and after hydrolytic degradation revealed prominent differences in the hydrolytic degradation process of rice bran and wood flour filled biocomposites. The water uptake and mass loss for polylactide/wood flour composites were similar to that of plain PLA. Pyrolysis-GC-MS, however, showed that on prolonged ageing the hydrolysis of PLA led to increased wood flour concentration in the remaining biocomposite matrices. In contrast, the polylactide/rice bran composites exhibited larger water uptake and higher mass loss. Pyrolysis-GC-MS and FTIR analysis proved that the higher mass loss was caused by migration of rice bran from the composites. The type of natural filler could thus greatly influence the degradation process and/or the stability of the materials in aqueous or humid environments.
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| 26. |
- Badia, J.D., et al.
(författare)
-
Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechanical performance
- 2012
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:4, s. 670-678
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PIA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PIA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystallization during DSC and DMTA measurements, which enthalpy increased with each reprocessing step, suggested chain scission due to thermo-mechanical degradation. The effect of chain shortening on the glass-rubber relaxation studied by DMTA showed an increase in free volume affecting the segmental dynamics of PLA, particularly after the application of the second reprocessing step, in connection to the overall loss of performance showed by the remaining properties.
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| 27. |
- Badia, J. D., et al.
(författare)
-
Relevant factors for the eco-design of polylactide/sisal biocomposites to control biodegradation in soil in an end-of-life scenario
- 2017
-
Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 143, s. 9-19
-
Tidskriftsartikel (refereegranskat)abstract
- The eco-design considers the factors to prepare biocomposites under an end-of-life scenario. PLA/sisal biocomposites were obtained from amorphous polylactide and sisal loadings of 10, 20 and 30 wt% with and without coupling agent, and subjected to biodegradation in soil according to standard ISO846. Mass-loss, differential scanning calorimetry and size-exclusion chromatography were used for monitoring biodegradation. A statistical factorial analysis based on the molar mass Mn and crystallinity degree XC pointed out the relevance and interaction of amount of fibre and use of coupling agent with the time of burial in soil. During the preparation of biocomposites, chain scission provoked a similar reduction of Mn for coupled and non-coupled biocomposites. The amount of fibre was relevant for the increase of XC due to the increase of nucleation sites. The coupling agent accelerated the evolution of both factors: reduction of Mn and the consequent increase of XC, mainly during biodegradation in soil. Both factors should be balanced to facilitate microbial assimilation of polymer segments, since bacterial digestion is enhanced by chain scission but blocked by the promotion of crystalline fractions.
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| 28. |
- Badia, J.D., et al.
(författare)
-
The role of crystalline, mobile amorphous and rigid amorphous fractions on the performance of recycled poly (ethylene terephthalate) (PET)
- 2012
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:1, s. 98-107
-
Tidskriftsartikel (refereegranskat)abstract
- The action of thermo-mechanical degradation induced by mechanical recycling of poly(ethylene terephthalate) was simulated by successive injection moulding cycles. Degradation reactions provoked chain scissions and a reduction in molar mass mainly driven by the reduction of diethyleneglycol to ethylene glycol units in the flexible domain of the PET backbone, and the formation ofeOH terminated species with shorter chain length. The consequent microstructural changes were quantified taking into account a three-fraction model involving crystalline, mobile amorphous (MAF) and rigid amorphous fractions (RAF). A remarkable increase of RAF, to a detriment of MAF was observed, while the percentage of crystalline fraction remained nearly constant. A deeper analysis of the melting behaviour, the segmental dynamics around the glass-rubber relaxation, and the macroscopic mechanical performance, showed the role of each fraction leading to a loss of thermal, viscoelastic and mechanical features, particularly remarkable after the first processing cycle.
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| 29. |
- Badía, José David, et al.
(författare)
-
Thermal analysis applied to the characterization of degradation in soil of polylactide : II. on the thermal stability and thermal decomposition kinetics
- 2010
-
Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 95:11, s. 2192-2199
-
Tidskriftsartikel (refereegranskat)abstract
- The disposal stage of polylactide (PLA) was assessed by burying it in active soil following an international standard. Degradation in soil promotes physical and chemical changes in the polylactide properties. The characterization of the extent of degradation underwent by PLA was carried out by using Thermal Analysis techniques. In this paper, studies on the thermal stability and the thermal decomposition kinetics were performed in order to assess the degradation process of a commercial PLA submitted to an accelerated soil burial test by means of multi-linear-non-isothermal thermogravimetric analyses. Results have been correlated to changes in molecular weight, showing the same evolution as that described by the parameters of thermal stability temperatures and apparent activation energies. The decomposition reactions can be described by two competitive different mechanisms: Nucleation model (A2) and Reaction Contracting Volume model (R3). The changes in the kinetic parameters and kinetic models are in agreement with the calorimetric and dynamic-mechanical-thermal results, presented in the Part I of the study [1]. © 2010 Elsevier Ltd. All rights reserved.
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| 30. |
- Badia, J. D., et al.
(författare)
-
Water absorption and hydrothermal performance of PHBV/sisal biocomposites
- 2014
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 108, s. 166-174
-
Tidskriftsartikel (refereegranskat)abstract
- The performance of biocomposites of poly(hydroxybutyrate-co-valerate) (PHBV) and sisal fibre subjected to hydrothermal tests at different temperatures above the glass transition of PHBV (T-H = 26, 36 and 46 degrees C) was evaluated in this study. The influences of both the fibre content and presence of coupling agent were focused. The water absorption capability and water diffusion rate were considered for a statistical factorial analysis. Afterwards, the physico-chemical properties of water-saturated biocomposites were assessed by Fourier-Transform Infrared Analysis, Size Exclusion Chromatography, Differential Scanning Calorimetry and Scanning Electron Microscopy. It was found that the water diffusion rate increased with both temperature and percentage of fibre, whereas the amount of absorbed water was only influenced by fibre content. The use of coupling agent was only relevant at the initial stages of the hydrothermal test, giving an increase in the diffusion rate. Although the chemical structure and thermal properties of water-saturated biocomposites remained practically intact, the physical performance was considerably affected, due to the swelling of fibres, which internally blew-up the PHBV matrix, provoking cracks and fibre detachment.
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| 31. |
- Bi, Ran, et al.
(författare)
-
The degree of acetylation affects the microbial degradability of mannans
- 2016
-
Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 133, s. 36-46
-
Tidskriftsartikel (refereegranskat)abstract
- Hemicelluloses as major components of plant cell walls are acetylated to different extents. The biologicalfunctions of acetylation are not completely understood but suggested that one reason is to decrease themicrobial degradability of cell walls. Model seed galactomannan and glucomannan, which are structurallysimilar to an abundant class of wood hemicelluloses, were acetylated to various degrees and usedas sole carbon source on agar plates for microbial growth. When soil samples were inoculated on theplates, significantly fewer strains grew on the agar plates with highly acetylated mannans than withslightly acetylated or non-acetylated mannans. One filamentous fungus isolated and identified as aPenicillium species was shown to grow faster and stronger on non-acetylated than on highly acetylatedmannan. The data therefore support the hypothesis that a high degree of acetylation (DSac) can decreasethe microbial degradability of hemicelluloses. Possible mechanisms and the technological significance ofthis are discussed.
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| 32. |
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| 33. |
- Breese, KD, et al.
(författare)
-
Improving synthetic hindered phenol antioxidants: Learning from vitamin E
- 2000
-
Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 70, s. 89-96
-
Tidskriftsartikel (refereegranskat)abstract
- The efficiency of various commercial hindered phenol antioxidants was studied using differential scanning calorimetry (DSC) to determine the oxidation induction time (OIT) of antioxidant solutions in squalane. It was observed that a-tocopherol has an exceptionally high antioxidant activity. In fact, after normalisation for the molecular weight and functionality of each antioxidant, a-tocopherol was twice as efficient as any of the commercial, synthetic, hindered phenols tested. Through measurements on a series of model compounds, it was possible to identify the aspects of a-tocopherol’s chemical structure that are responsible for it’s exceptional antioxidant efficiency. The results showed that the para oxygen in a-tocopherol is largely responsible for it’s exceptionally high antioxidant activity. Most commercial synthetic hindered phenolic antioxidants are based upon 2, 6-di-tert-butyl-4-methylphenol (BHT). We compared the antioxidant efficiency of BHT with that of 2, 6-di-tert-butyl-4-methoxyphenol (BHA) and found that BHA was 94% more efficient. This implies that it may be advantageous to make new commercial hindered phenolic antioxidants that are based in the more effective BHA structure instead of the conventional BHT structure used today. It is expected that addition of a para oxygen (or other electron donating groups) to the aromatic ring of existing hindered phenolic antioxidants would significantly increase their activity.
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| 34. |
- Burman, Lina, et al.
(författare)
-
Chromatographic Fingerprinting - a Tool for Classification and for Predicting the Degradation State of Degradable Polyethylene
- 2005
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 89:1, s. 50-63
-
Tidskriftsartikel (refereegranskat)abstract
- The number of degradable polyethylene films on the market is increasing. These degradable films show different degradation behaviour depending on the pro-oxidant system incorporated in them. The degradation of the films gives rise to complex collections of degradation products. The key question in this work was to classify the types of pro-oxidant systems in degradable polyethylene films and the state of degradation of the films. The classification was performed with chromatographic fingerprints of carboxylic acids, the most abundant type of degradation product. The acids were extracted from films oxidised at 80 ° C and were thereafter methylated and analysed by GC-MS. Classification and prediction models were obtained by Multivariate Data Analysis. The diacids were grouped according to both the type of pro-oxidant system and the state of degradation. This showed that both the type of pro-oxidant system and the state of degradation are predictable from the diacid fingerprints. The monoacids were shown to be useful for classifying materials from their initial compositions of stearates but not for predicting the degradation state. The goal was also to see how changes in activation energies for hydroperoxides, noticed earlier with chemiluminescence, were reflected in the degradation mechanisms. The observed increase in chemiluminescence peak temperature of the polyoctylene-containing film was related to the initial degradation of the polyoctylene.
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| 35. |
- Butylina, Svetlana, et al.
(författare)
-
A study of surface changes of wood-polypropylene composites as the result of exterior weathering
- 2012
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 97:3, s. 337-345
-
Tidskriftsartikel (refereegranskat)abstract
- Outdoor applications of composites raised questions about their durability. In this study, the effects of outdoor weathering on the properties of wood-polypropylene composites with and without pigments were examined. The composites were placed outdoors for one year, and their colour changes were evaluated after 1, 3, 6, 9 and 12 months of weathering. The weathering resulted in considerable colour fading of the composites. Composites containing darker colour pigments had better colour stability. Scanning electron microscopy analysis revealed that surface cracks caused by weathering in a wood-polypropylene composite having a higher polypropylene content were less abundant, and the deterioration of the surface layer was lower compared to composites containing less polymer. Measurements of melting temperatures by differential scanning calorimetry gave a consistent picture of polypropylene degradation in the surface layer. After weathering, a decrease in Charpy impact strength was found for composites characterised by higher moisture absorption.
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| 36. |
- Butylina, Svetlana, et al.
(författare)
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Weathering properties of coextruded polypropylene-based composites containing inorganic pigments
- 2015
-
Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 120, s. 10-16
-
Tidskriftsartikel (refereegranskat)abstract
- This study concerns the weathering properties of coextruded polypropylene-based composites containing pigments. Three different pigments were incorporated in the shell layer of the composites: iron oxide, titanium dioxide and zinc oxide. The surface colour, surface gloss and tensile properties were tested. In addition, the weathered surfaces were studied by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The surfaces of the composites containing inorganic pigments were found to have fewer cracks after 500 h of weathering than the surface of the reference composite. The results revealed that the composites containing titanium oxide pigment exhibited better colour stability than the composites made with the other pigments. In spite of its high colour stability in weathering, the tensile properties (strength, Young's modulus and elongation at break) of the composite containing titanium oxide were reduced by weathering. The FTIR analysis revealed that the composite containing zinc oxide had a stabilising effect on polypropylene photo-degradation, which correlates well with the results of mechanical testing, showing that this composite retained its mechanical properties after weathering
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| 37. |
- Camacho, W., et al.
(författare)
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Quality-determination of recycled plastic packaging waste by identification of contaminants by CC-MS after microwave assisted extraction (MAE)
- 2000
-
Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 71:1, s. 123-134
-
Tidskriftsartikel (refereegranskat)abstract
- The quality of recycled resins of high density polyethylene (HDPE) and polypropylene (PP) separated from mixed solid waste (MSW) were studied by analyzing the tentative low molecular weight contaminants. For that purpose a microwave assisted extraction (MAE) technique was developed using MDPE and two aromatic antioxidants (Irganox 1010 and Irgafos 168) as models. A 50:50 mixture of cyclohexane and isopropanol gave high recovery yields; 97% for Irgafos 168 and 93% for Irganox 1010 and short extraction times. Limonene, isopropylester of myristic and palmitic acids were examples of products identified in recycled HDPE. These compounds are typically fragrance and flavor constituents. In addition alcohols, esters, ketones were identified. Most of the substances are constituents of the packaging fillings at their first usage. But the possibility that contaminants may have entered the material by contact with other plastics is not excluded. The major category of compounds identified already in the virgin material is composed of aliphatic hydrocarbons (e.g. pentadecane, hexadecaned, 1-hexadenene), branched alkanes, branched alkenes and others. The same kind of compounds were also identified in the recycled materials at a similar concentration as in virgin ones. Virgin and recycled polyethylene contain also ethylbenzene and o-, m- and p-xylenes, where o-xylene had the largest peak of the four. The aromatic hydrocarbons are probably parts of additives, which degraded during extraction and sample preparation procedures. Aromatic hydrocarbons without functional groups, such as ethylbenzene and xylenes are considered highly toxic, but the height and area of their peaks suggest low concentrations. The concentration of these hazardous contaminants in the recycled resin is, however, approximately five times higher in recycled material, estimated by a comparison of the peak areas. Ethylbenzene and o-, m- and p-xylenes, o-xylene having the largest peak of the four were also identified in virgin and recycled polypropylene resins.
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| 38. |
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| 39. |
- Dalborg, M., et al.
(författare)
-
Methods for determining the spatial distribution of oxidation in ultra-high molecular-weight polyethylene prostheses
- 2007
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 92:3, s. 437-447
-
Tidskriftsartikel (refereegranskat)abstract
- Oxidative degradation is a well-known problem for UHMWPE used in prostheses. The aim of the present study has been to find suitable techniques to study the spatial distribution of this oxidation in 8 retrieved acetabular cups. The techniques used were visual examination using an optical microscope and computer scanner, FTIR mapping, imaging chemiluminescence, and staining with SO2 and HCl. The staining technique is based on a previous study which showed that by treating oxidized UHMWPE with SO2 followed by heat treatment, the hydroperoxides present in the sample react with the SO2 and discolor the sample. The intensity of this discoloring is, at low levels of oxidation, proportional to the amount of hydroperoxides and accordingly to the level of the oxidation. The same study also showed that staining a sample with hot HCl resulted in a brown discoloration which was proportional to the amount of carbonyls. It was found that the staining techniques do not give as much information about the chemical and physical changes in the material as FTIR mapping but have a great advantage in better spatial resolution of the oxidation and are also much quicker and easier to use. Imaging chemiluminescence turned out not to be a suitable method to use, compared to the other two, since it gives less information and is more difficult to interpret. When interpreting the results from the different techniques used, it was found that all cups showed the typical oxidation behavior of gamma sterilized UHMWPE. All cups but one showed substantial wear of the articulating surface but very little backside wear. Examination of the oxidation and whitening profile suggests that at least some of the oxidation must have occurred in vivo.
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| 40. |
- Das, Oisik, et al.
(författare)
-
Biochar to the rescue : Balancing the fire performance and mechanical properties of polypropylene composites
- 2017
-
Ingår i: Polymer degradation and stability. - : ELSEVIER SCI LTD. - 0141-3910 .- 1873-2321. ; 144, s. 485-496
-
Tidskriftsartikel (refereegranskat)abstract
- Biochar based wood/polypropylene (PP) composites were manufactured with two flame retardants (FRs): ammonium polyphosphate/APP and magnesium hydroxide/Mg(OH)(2). The amounts of wood and biochar were alternated for accommodating the FRs in each blend. Flammability and mechanical characterisation for both the batches containing different FRs were done. Having higher proportion of biochar and less wood is beneficial to reduce flammability. The thermally stable biochar contributes to formation of effective char to restrict O-2 transfer into PP. The higher weight ratio of biochar than wood in the composites compromised the tensile and flexural strengths to some extent as the APP and Mg(OH)(2) particles were trapped inside biochar pores consequently reducing the effectiveness of biochar pore infiltration by PP. In general, addition of biochar with a woody biomass (with FRs) to neat PP significantly impedes its flammability while enhancing certain mechanical properties, such as flexural strength and tensile/flexural moduli and preserving the tensile strength. (C) 2017 Elsevier Ltd. All rights reserved.
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| 41. |
- Di Filippo, Maria, et al.
(författare)
-
Hydrothermal aging of carbon reinforced epoxy laminates with nanofibrous mats as toughening interlayers
- 2016
-
Ingår i: Polymer degradation and stability. - : Elsevier. - 0141-3910 .- 1873-2321. ; 126, s. 188-195
-
Tidskriftsartikel (refereegranskat)abstract
- Electrospun mats have been applied as toughening interlayers in high performance carbon fiber epoxy composites. While the toughening mechanism exerted by the mat at the interface is the subject of several recent studies, no investigations are reported on the aging behaviour of laminates comprising these nanostructured elements. This work investigates the influence of the combined effect of water and temperature (90 degrees C) on laminates with Nylon 6,6 electrospun membranes placed either at the middle plane only or at each interlayer. The water-uptake behaviour is modelled by a two-stage diffusion model and compared with the behaviour of the neat resin and of the laminate without mats. Interestingly, a lower water uptake is observed for the laminates with mat-modified interfaces and this is possibly due to a significantly reduced porosity. The effect of hydrothermal aging on the thermal (Tg) and mechanical properties (transverse flexural modulus and interlaminar shear strength) of the various laminates is also investigated.
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| 42. |
- Ekelund, Maria, et al.
(författare)
-
Evaporative loss kinetics of di(2-ethylhexyl)phthalate (DEHP) from pristine DEHP and plasticized PVC
- 2010
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 95:9, s. 1789-1793
-
Tidskriftsartikel (refereegranskat)abstract
- The migration of di(2-ethylhexyl)phthalate (DEHP) from poly(vinyl chloride) (PVC) to a surrounding gas phase at temperatures below 120 degrees C kinetically is controlled by evaporation. The effects on the DEHP loss rate of nitrogen flow rate, relative humidity and degradation of the plasticizer at 100 degrees C was assessed. The sample mass decreased linearly with time for both pristine DEHP and plasticized PVC at comparable rates, suggesting that a thin film of DEHP was present on the jacketing insulation during desorption. The latter hypothesis was supported by infrared spectroscopy and by the fact that DEHP is an amphiphilic molecule that will tend to aggregate at the surface with the hydrophobic 2-ethylhexyl units at the air interface. The effect on the migration rate of moisture present in the gas phase was negligible. The DEHP loss rate increased in a retarding non-linear fashion with increasing gas flow rate. In one of the experiments, DEHP was accidently degraded as revealed by discoloration, the presence of low molar mass degradation products (liquid chromatography) containing additional carbonyl groups (infrared spectroscopy) and an increase in the evaporation rate at temperatures between 100 and 130 degrees C. (C) 2010 Elsevier Ltd. All rights reserved.
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| 43. |
- Ekelund, Maria, et al.
(författare)
-
Long-term performance of poly(vinyl chloride) cables. Part 1 : Mechanical and electrical performances
- 2007
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 92:4, s. 617-629
-
Tidskriftsartikel (refereegranskat)abstract
- Cables insulated with plasticized poly(vinyl chloride) were aged in air at temperatures between 80 degrees C and 180 degrees C and their conditions were assessed by indenter modulus measurements, tensile testing, infrared (IR) spectroscopy and differential scanning calorimetry (DSC). Electrical testing of oven-aged cable samples was performed in order to relate the electrical functionality during a high-energy line break (HELB) to the mechanical properties and to establish a lifetime criterion. The mechanical data taken at room temperature after ageing could be superimposed with regard to ageing time and temperature. The ageing-temperature shift factor showed an Arrhenius temperature dependence. The jacketing material showed an immediate increase in stiffness (indenter modulus and Young's modulus) and a decrease in the strain at break on ageing; these changes were dominated by loss of plasticizer by migration which was confirmed by IR spectroscopy and DSC. The core insulation showed smaller changes in these mechanical parameters; the loss of plasticizer by migration was greatly retarded by the closed environment, according to data obtained by IR spectroscopy and DSC, and the changes in the mechanical parameters were due to chemical degradation (dehydrochlorination). A comparison of data obtained from this study and data from other studies indicates that extrapolation of data for the jacketing insulation can be performed according to the Arrhenius equation even down to service temperatures (20-50 degrees C). The low-temperature deterioration of the jacketing is, according to this scheme, dominated by loss of plasticizer by migration.
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| 44. |
- Ekelund, Maria, et al.
(författare)
-
Long-term performance of poly(vinyl chloride) cables, Part 2 : Migration of plasticizer
- 2008
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 93:9, s. 1704-1710
-
Tidskriftsartikel (refereegranskat)abstract
- Cable samples with plasticized poly(vinyl chloride) insulations were aged in air at temperatures between 80 and 155 degrees C. The concentrations of the plasticizer (di-(2-ethylhexyl) phthalate, DEHP) in the insulations of the aged cables were determined by extraction of samples in tetrahydrofuran followed by analysis of the extract by liquid chromatography. The plasticizer concentration data for different ageing times were analysed by numerical methods, fitting Fick's second law with a concentration-dependent diffusivity. The analysis showed that the transport of the plasticizer to the surrounding air phase was controlled by diffusion at 120 and 155 degrees C with an activation energy of 89 kJ mol(-1). The evaporation of the plasticizer from the outer boundary was rate controlling at lower temperatures (<= 100 degrees C), The rate of evaporation was initially constant and independent of the plasticizer concentration at both 80 and 100 degrees C. The activation energy for the initial DEHP loss rate from PVC at these temperatures was the same as that obtained for evaporation of pure DEHP on a glass plate at 60-100 degrees C measured by thermogravimetry, 98 2 kJ mol-1. Furthermore, the evaporation rate of pure DEHP on a glass plate was also of the same order of magnitude as the rate of plasticizer loss from the cable insulation. Extrapolation of the plasticizer loss rate data (from the cable at 80 degrees C and from pure liquid DEHP at temperatures between 60 and 100 IQ to 25 degrees C predicted a maximum loss of plasticizer of 1% over 25 years. This is in accordance with earlier presented data and with the data presented in this report.
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| 45. |
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| 46. |
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| 47. |
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| 48. |
- Espert, Ana, et al.
(författare)
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Emission of possible odourous low molecular weight compounds in recycled biofibre/polypropylene composites monitored by head-space SPME-GC-MS
- 2005
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 90:3, s. 555-562
-
Tidskriftsartikel (refereegranskat)abstract
- A disadvantage of the use of natural fibres to reinforce polypropylene is their poor thermal stability, which results in their degradation at processing temperatures of the composites. As a result of this, there is a formation of low molecular weight compounds that are responsible for undesirable odours. Head-space-solid phase microextraction (HS-SPME) was used as a sample preparation technique and gas chromatography-mass spectrometry (GC-MS) was used to identify the low molecular weight compounds in natural polypropylene/polypropylene composites after simulating degradation. Among the compounds found in the samples, there are fragments of PP chains as heptadecane, compounds from antioxidants such as 2,4-bis(1,1-dimethylethyl)-phenol, and p-tert-butylphenol, and compounds from biofibres ageing, such as ethylparaben and vanillin. Numerous carboxylic acids were also identified, being these most probably the source of the undesirable odours.
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| 49. |
- Fateh-Alavi, Kamyar, et al.
(författare)
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Effect of stabilizers on surface oxidation of silicone rubber by corona discharge
- 2004
-
Ingår i: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 84:3, s. 469-474
-
Tidskriftsartikel (refereegranskat)abstract
- Crosslinked polydimethylsiloxane (PDMS) containing Irganox(R) 1076, Tinuvin(R) 770 or lrganox(R) 565, prepared by swelling PDMS in a solution of one of these stabilizers in n-hexane, was exposed to a corona discharge and the corona exposure time (tau(crit)) to form a brittle, silica-like layer was determined by optical microscopy. The critical corona exposure time showed a linear increase with increasing stabilizer concentration; Tinuvin 770 showed the highest efficiency and Irganox 1076 the lowest. The increase in tau(crit) on corona exposure of the stabilized samples with reference to the value for unstabilized PDMS was similar to that reported earlier for air plasma exposed samples. The efficiency of the stabilizers towards corona-induced surface oxidation of PDMS was also confirmed by X-ray photoelectron spectroscopy.
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| 50. |
- Forsgren, Lilian, 1990, et al.
(författare)
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The thermo-oxidative durability of polyethylene reinforced with wood-based fibres
- 2020
-
Ingår i: Polymer degradation and stability. - : Elsevier Ltd. - 0141-3910 .- 1873-2321. ; 181
-
Tidskriftsartikel (refereegranskat)abstract
- Aiming at better understanding the ageing behaviour of cellulose composites, the accelerated thermo-oxidative ageing of polyethylene reinforced with two types of wood-based cellulose fibres was studied. Materials were prepared by extrusion mixing of either un-stabilized or stabilized polyethylene reinforced with 5 and 20 vol % cellulose content. The materials were extruded into strips and then aged at 90°C in circulating air. The effect of accelerated ageing up to 31 days was assessed by oxidation induction time and mechanical properties in tension. The results indicated that the added cellulose fibres did not increase the degradation of the composites during this ageing. Reinforcement with 20 % cellulose fibre having a 28 % lignin content together with 0.005 % Irganox 1010 antioxidant resulted in a remarkable improvement in the resistance against accelerated thermo-oxidation, compared to the pure polyethylene with added antioxidant. The findings of increased lifetime of LDPE by addition of wood-based reinforcement is of great interest, since the durability aspect is crucial to understand and predict before usage in commercial applications and especially as structural composites.
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