| 11. |
- Camacho, W., et al.
(författare)
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Simultaneous determination of molecular weight and crystallinity of recycled HDPE by infrared spectroscopy and multivariate calibration
- 2002
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 85:2, s. 321-327
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Tidskriftsartikel (refereegranskat)abstract
- An attempt of correlating molecular weight (M,) of recycled high-density polyethylene (HDPE) as measured by size-exclusion chromatography (SEC) with diffuse reflectance near and mid-infrared spectroscopy (NIR/MIR) was made by means of multivariate calibration. The spectral data obtained was also used to extract information about the degree of crystallinity of the recycled resin. Differential scanning calorimetry (DSC) was used as the reference method. Partial leastsquares (PLS) calibration was performed on the MIR and NIR spectral data for prediction of Af, Four PC factors described fully the PLS models. The root-meansquare error of prediction (RMSEP) obtained with MIR data was 360, whereas a RMSEP of 470 was achieved when calibration was carried out on the diffuse reflectance NIR data. A PLS calibration for prediction of degree of crystallinity was performed on the NIR data in the 1100-1900-nm region, but the ability of prediction of this model was poor. However a PLS calibration in the region 2000-2500 nm yield better results. Four PC factors explained the most of the variance in the spectra and the RMSEP was 0.4 wt %.
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| 12. |
- Contat-Rodrigo, L., et al.
(författare)
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Ultrasonication and microwave assisted extraction of degradation products from degradable polyolefin blends aged in soil
- 2001
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 79:6, s. 1101-1112
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Tidskriftsartikel (refereegranskat)abstract
- Two nonconventional extraction techniques, microwave assisted extraction (MAE) and ultrasonication, were used to extract degradation products from polyolefins with enhanced degradability. High-density polyethylene/polypropylene blends with two different biodegradable additives (a granular starch/iron oxide mixture and Mater-Bi AF05H) were subjected to outdoor soil burial tests and removed at different periods of time between 0 and 21 months. The extracted products were analyzed by gas chromatography mass spectrometry (GC-MS). Ultrasonication was found to be a more suitable technique than MAE because of better reproducibility. In addition, higher amounts of certain products (e.g., carboxylic acids) were extracted by ultrasonication than by MAE. The degradation products extracted from the two blends were basically a homologous series of alkanes, alkenes, carboxylic acids, and alcohols. The amount of hydrocarbons (saturated and unsaturated) and alcohols remained basically the same as the degradation times increased. However, carboxylic acids tended to decrease slightly with the exposure time. Their concentration remained practically unchanged until 12 months of soil burial when a more significant decrease was noted. The quantitative analysis of the degradation products revealed for both samples a decrease in the amount of carboxylic acids with the exposure time, although the trend was different according to the additive used in each sample. For blends with Mater-Bi the amount of carboxylic acids was at a minimum after 12-month exposure in soil, which coincided with a minimum in the molecular weight distribution. After blends with granular starch/iron oxide were exposed to 3 months in soil, tetradecanoic acid was no longer detectable and the amount of hexadecanoic and octadecanoic acids decreased significantly. Solid-phase microextraction, a solvent-free extraction technique, was used to extract the degradation products that could have migrated to the soil from blends with Mater-Bi. Small amounts of tetradecanoic acid and dodecanol were identified by GC-MS in the soil surrounding the sample. The degradation patterns observed here correlate with our previous results from mechanical and morphological characterization of these samples.
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| 13. |
- Eldsater, C., et al.
(författare)
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Changes in composition of hydrolyzed poly(butylene adipate-co-caproamide) characterized by pyrolysis-GC-MS, H-1-NMR and FTIR
- 2000
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Ingår i: IJPAC. International journal of polymer analysis and characterization. - : Informa UK Limited. - 1023-666X .- 1563-5341. ; 5:06-apr, s. 415-435
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Tidskriftsartikel (refereegranskat)abstract
- The changes in composition of an abiotically degraded polyester-amide, poly(butylene adipate-co-caproamide), in an aqueous environment at 37 degrees C; 60 degrees C and 80 degrees C were investigated. The changes in polymer composition were studied using pyrolysis-GC-MS, H-1-NMR, FTIR, and size exclusion chromatography, and degradation products were analyzed by solid-phase extraction and subsequent GC-MS. During the degradation of PEA in an aqueous environment, the main degradation products were 6-aminohexanoic acid, 1-hydroxydodecanoic acid-6-one-5-oxo and dimers. After longer degradation times and at higher degradation temperatures, 1-hydroxydodecanoic acid-6-one-5-oxo was cleaved further into hexanedioic acid and 1,4-butanediol. At 80 degrees C, the degradation was fastest with the largest weight loss due to dissolution of oligomer. At 80 degrees C, the amide content in the copolymer increased with increasing degradation time. We suggest that there is a two-step degradation mechanism with the formation of linear degradation products, where the hydrolysis of ester bonds is favored over that of amide bonds.
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| 14. |
- Espert, Ana, et al.
(författare)
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Comparison of water absorption in natural cellulosic fibres from wood and one-year crops in polypropylene composites and its influence on their mechanical properties
- 2004
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Ingår i: Composites. Part A, Applied science and manufacturing. - : Elsevier BV. - 1359-835X .- 1878-5840. ; 35:11, s. 1267-1276
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Tidskriftsartikel (refereegranskat)abstract
- Environmentally beneficial composites can be made by replacing glass fibres with various types of cellulose fibres. Fibres from pine or eucalyptus wood and also one-year crops such as coir, sisal, etc. are all good candidates. The poor resistance towards water absorption is one of the drawbacks of natural fibres/polypropylene composites. New natural fibres/polypropylene composites were made and the water absorption in them was studied by immersion of the composites in water at three different temperatures, 23, 50 and 70 degreesC. The process of absorption of water was found to follow the kinetics and mechanisms described by Fick's theory. In addition, the diffusivity coefficient was dependent on the temperature as estimated by means of Arrhenius law. A decrease in tensile properties of the composites was demonstrated, showing a great loss in mechanical properties of the water-saturated samples compared to the dry samples. The morphology change was monitored by scanning electron microscopy studies of the samples before and after exposure to water and the devastating effect of water on the fibre structure was shown.
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| 15. |
- Espert, Ana, et al.
(författare)
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Thermal and thermomechanical properties of biocomposites made from modified recycled cellulose and recycled polypropylene
- 2003
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 89:9, s. 2353-2360
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Tidskriftsartikel (refereegranskat)abstract
- Residual cellulose fibers from the paper industry have been used as reinforcements in recycled polypropylene (PP) composites. The main obstacle to obtaining good properties with this biocomposite is deficiencies in the compatibility between the nonpolar matrices and the polar cellulose fibers used as reinforcements. The aim of this work was to improve the compatibilization between these cellulose fibers and the PP matrix with four different methods: modification by the addition of polypropylene-maleic anhydride copolymer (PPgMA) during the process of blending, preblending modification of the cellulose with a solution of PPgMA, modification of cellulose by silanes (vinyltrimethoxysilane), and acetylation of cellulose. Blends with all of the differently modified celluloses were prepared with the cellulose content varied up to 40%, and then all of the blends were subjected to thermal (differential scanning calorimetry and thermogravimetric analysis) and thermomechanical (dynamic mechanical thermal analysis) analyses. The results showed that the addition of cellulose fibers improved the thermomechanical behavior of the PP, increasing the value of the log of the dynamic modulus, and affected the thermal and thermooxidative behavior. Moreover, an advantage of the use of a recycled PP containing a small quantity of ethyl vinyl acetate (EVA) as a prime material in the composition was the enhancement of mechanical properties. The use of these methods for the modification of cellulose led to more desirable thermal and thermooxidative stabilities.
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| 16. |
- Fateh-Alavi, Kamyar, et al.
(författare)
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A rapid microwave-assisted solvent extraction method for assessment of stabilizer concentration in crosslinked polydimethylsiloxane
- 2004
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 93:5, s. 2185-2192
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Tidskriftsartikel (refereegranskat)abstract
- Crosslinked polyclimethylsiloxanes were prepared containing 0.05 to 0.2 wt % of either a phenolic antioxidant (Irganox(R) 1010) or a hindered amine stabilizer (Tinuvin(R) 144). The stabilizer concentration was assessed by HPLC and UV-Vis spectroscopy of Soxhlet and microwave-assisted solvent extracts. Almost complete recovery of stabilizer was achieved with Soxhlet extraction. High stabilizer recovery was achieved when acetone was used as the solvent in the microwave-assisted extraction. HPLC was shown to be an efficient method for determining the concentration of Irganox 1010. For Tinuvin 144 the selectivity of both UV-Vis spectroscopy and HPLC was poor, leading to imprecise evaluation of the antioxidant concentration. The loss of stabilizer by migration from polymer to hot water (75 and 95degreesC) was monitored for the systems stabilized with Irganox 1010 and the diffusion coefficient of the antioxidant in the polymer was determined.
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| 17. |
- 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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| 18. |
- Gallet, G., et al.
(författare)
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Characterisation by solid phase microextraction-gas chromatography-mass spectrometry of matrix changes of poly(L-lactide) exposed to outdoor soil environment
- 2000
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Ingår i: Polymer degradation and stability. - 0141-3910 .- 1873-2321. ; 71:1, s. 147-151
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Tidskriftsartikel (refereegranskat)abstract
- Films of poly(L-lactide), PLLA, were buried in outdoor environment in south Finland during two years. The changes in polylactide matrix were characterised by size exclusion chromatography and differential scanning calorimetry, and formation of volatile oligomers was monitored by solid phase microextraction (SPME)-gas chromatography-mass spectrometry. SPME sample preparation was found suitable for analysing small volatile compounds in solid PLLA samples. The oligomers in polylactide were readily extracted with polar CW/DVB fibre. The oligomers were analysed without any complicated sample handling procedure and no solvent was needed. Lactic acid, lactide and lactoyl lactic acid were extracted from the unaged and aged films. Lactide was observed in all films and its content did not change during the two years of soil burial. No lactic acid was observed in any of the polylactide films during the first year. After 20 months lactic acid and lactoyl lactic acid appeared as a result of hydrolysis. After 24 months the amount of lactoyl lactic acid decreased due to biotic hydrolysis of the film. The molecular weight M-n of polylactide increased and the polydispersity decreased during the first year. A slow chemical hydrolysis combined with the migration of small oligomers in soil caused the molecular weight changes for this period. During the second year of soil burial both M-n, and M-w decreased and the polydispersity decreased towards 2. This indicates that a faster hydrolysis took place in the film. It was confirmed by the differential scanning calorimetry analysis of PLLA, which showed that during the second year in soil the thermal properties of the films (T-g and T-m) were affected. PLLA was thus degraded by a combination of hydrolysis and biotic activity. In a first stage, after an induction period of 1 year, the film of PLLA undergoes hydrolysis. In a second stage microorganisms assimilate the small products of degradation while hydrolysis takes place.
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| 19. |
- Gallet, G., et al.
(författare)
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Thermal degradation of poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer : comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:4, s. 1081-1094
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Tidskriftsartikel (refereegranskat)abstract
- By comparing size exclusion chromatography/matrix assisted laser desorption ionisation (SEC/MALDI) and SEC/NMR spectra from virgin poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, we were able to understand the bimodal distribution observed in poloxamer 407. Propylene oxide, isomerised to allyl alcohol during polymerisation, eventually forms a Poly(ethylene oxide-propylene oxide) diblock copolymer when EO is added to the feed. The oxidative thermal degradation of poloxamer 407 at 80 degreesC in air was studied. We found by MALDI that degradation starts after 21 days in the PPO block of the copolymer. This result was confirmed by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS): The first volatile degradation product to appear is 1,2-propanediol,1-acetate,2-formate. The structure of this molecule suggests that a six-ring intramolecular decomposition reaction of the PPO chain occurs at the very beginning of the polymer breakdown. Thus, the secondary hydroperoxide formed on the PPO chain plays a major role on the thermoxidation of poloxamer materials.
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| 20. |
- 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
-
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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