| 1. |
- Alin, Jonas
(författare)
-
Microwave heating effects on degradation and migration of additives from polypropylene packaging
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The effect of different food types, polymer qualities and microwaves on the overall and specific migration during microwave heating of plastic packaging was investigated to better understand the packaging-food interactions and the effect of microwaves on food packaging. This work focuses on the migration of chemical compounds to food simulants from commercially available polypropylene packages. Packages used were made of polypropylene homopolymer (PP), co-polymer (PP-C) and random co-polymer (PP-R). Polymers matrix changes were monitored by following possible changes in crystallinity after microwave heating. Antioxidants Irgafos 168 and Irganox 1010 were present in all the three PP packages. Other volatiles, primarily degradation products of antioxidants, were also detected and identified in the unaged packages. Significant antioxidant degradation took place during microwave heating of the packages in the fatty food simulants 90/10 isooctane/ethanol and ethanol resulting in the formation and migration of degradation products while no degradation of antioxidants was detected during conventional heating of the packages in the fatty food simulants. Antioxidant Irgafos 168 and Irganox 1010 migration rates were otherwise similar during microwave heating as during conventional heating to the fatty food simulants and antioxidant diffusion coefficients were similar to earlier established values obtained during conventional heating. Antioxidant migration rates from the three polymers to fatty food simulants differed largely with respect to PP type and increased with decreasing degree of crystallinity in the materials, PP-R showing the highest migration rate. Swelling in isooctane food simulant caused the antioxidant diffusion coefficients to increase by factors of 100-1000 at 80 ºC and decreased the temperature dependence of antioxidant migration. It also increased the overall migration to above established overall migration limits during both microwave and conventional heating. Electrospray ionization mass spectrometry (ESI-MS) was shown to be a valuable new tool for additive migration analysis of compounds not detectable by HPLC or GC-MS.
|
|
| 2. |
- Regnell Andersson, Sofia
(författare)
-
Tuning the polylactide hydrolysis rate without introducing new migrants
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The possibility to control and tune the hydrolytic degradation rate of polylactide without introducing any new degradation products was investigated by subjecting polylactide with cyclic or linear oligolactic acid additives, and a stereocomplex between the L- and D-enantiomers of polylactide to hydrolytic degradation at 37 and 60 °C for up to 39 weeks. The degradation was monitored by measuring mass loss, molar mass changes, water uptake, changes of surface structure, crystallinity and thermal properties. The degradation product pattern was followed through pH measurements and by electrospray ionization-mass spectrometry (ESI-MS). Rapid migration of additives from the material into the aging medium was observed in the case of the more hydrophilic linear oligolactic acid additives. The mass loss at 37 °C was generally 10-20 % greater for the material containing linear additives instead of cyclic additives. The hydrolysis accelerating effect of the linear additives may be counteracted by the facilitated crystal formation of the short chains. Micrographs showed formation of holes on the surface of the material containing linear additives during degradation. This may be a result of migration of phase separated linear additives. Phase separation might take place in the material as the crystallinity increases. The stereocomplex had a higher hydrolytic stability, which is explained by the strong interactions between the complementary chain structures. At 37 °C, the observed mass loss was generally 15 % lower for the stereocomplex compared to the material containing the cyclic additives. However, a larger amount of short hydroxy acids was released from the stereocomplex material, as shown by the large pH drop and the degradation product pattern analysed using ESI-MS. This can be explained by increased intermolecular stereocomplex crystallisation, which results in a larger number of tie-chains between crystals which are susceptible to hydrolysis and facilitate the formation of shorter hydrolysis products. Hydrolysis at 60 °C, i.e. above the glass transition temperature, was drastically faster and the differences between the materials were not as obvious as at the lower temperature. A large advantage using different forms of lactide or lactic acid as additives is that no new migrants are introduced into the degradation product pattern.
|
|
| 3. |
- Cho, Sung-Woo
(författare)
-
Aging and heat-sealing properties of films based on wheat gluten
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recently the research interest of the possibility of using wheat gluten (WG) as packaging material has greatly increased due to its combination of high gas barrier, attractive mechanical, film-forming and renewable properties. The source is also readily available and inexpensive on a worldwide basis. The glycerol-plasticized WG films cast from pH 4 and pH 11 solutions were investigated in order to understand the mechanisms behind the undesired aging. The film prepared from the pH 11 solution was mechanically more stable upon aging than the pH 4 film, which was initially very ductile but turning brittle with time. It was revealed that the protein structure of the pH 4 film was initially less polymerized/aggregated and the polymerization increased during storage but it did not reach the degree of aggregation of the pH 11 film, whereas deamidation was occurred and increased in the pH 11 film. During aging, the pH 4 film lost more mass than the pH 11 film mainly due to migration of glycerol but also due to some loss of volatile mass and the greater plasticizer loss of pH 4 film was presumably due to its initial lower degree of protein aggregation /polymerization. The glycerol migration of cast films exposed to a porous paper was further investigated with respect to pH of cast solution, glycerol content and film thickness since it was the main reason for deterioration of the properties. The opacity was also characterized. The glycerol migration was quantified using GC method in order to determine only glycerol content, but not other volatile substances. Glycerol content did not significantly change the opacity and pH 4 films showed good contact clarity because of less Maillard reaction. Glycerol was extensively migrating to the paper support and the migration seemed to be diffusion controlled. The heat sealability of WG films was investigated, using an impulse-hear sealer. It was observed that the WG films were readily sealable keeping up their integrity. The sealing temperature had a negligible effect on the lap-shear strength, but the peel strength increased with sealing temperature. The lap-shear strength increased with increasing mold temperature and the failure mode changed.
|
|
| 4. |
- Ekelund, Maria, 1977-
(författare)
-
Long-term performance of poly(vinyl chloride) cables : mechanical and electrical performances and the effect of plasticizer migration
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cables insulated with plasticized poly(vinyl chloride) were aged at temperatures between 80 and 180 °C in air and their conditions were assessed by indenter modulus measurements, tensile testing, infrared (IR) spectroscopy, differential scanning calorimetry (DSC) and liquid chromatography (HPLC). Electrical testing of oven-aged cable samples was performed in order to relate the electrical functionality during a high-energy line break accident 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 Arrhenius temperature dependence. The jacketing material showed an immediate increase in stiffness (indenter and Young’s modulus) and a decrease in the strain at break on ageing; these changes were dominated by loss of plasticizer by migration also confirmed by IR spectroscopy, DSC and HPLC. The core insulation showed smaller and also delayed changes in these mechanical parameters; the loss of plasticizer by migration was retarded by the closed environment and the changes in the mechanical parameters were due to chemical degradation (dehydrochlorination). Comparison with data obtained from this study and 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 (20-40 °C). Extraction of plasticizer of samples from cables that have been exposed to service for 25 years showed a minor decrease (within the margin of error) in plasticizer content with reference to that of unexposed cable samples. The low temperature deterioration of the jacketing is according to this scheme dominated by loss of plasticizer by migration. Numerical analysis were performed on desorption data obtained by liquid chromatography. The fitting of the data to Fick’s law showed a transition between 100 and 120 ºC. This was interpreted as a change from evaporation-control of migration at low temperatures to a diffusion-control of migration at the higher temperatures.
|
|
| 5. |
- Kim, Hyeri, et al.
(författare)
-
Toward Sustaining Bioplastics : Add a Pinch of Seasoning
- 2023
-
Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 11:5, s. 1846-1856
-
Tidskriftsartikel (refereegranskat)abstract
- Modern society can no longer sustain accumulating plastic pollution without intervention; plastic waste has even found its way into the food that we consume. Unfortunately, biodegradable alternatives lack sound commercial and economic distinctiveness because mechanical strength and biodegradability are typically mutually exclusive. Inspired by fine cuisine, we introduce a novel synthetic method, referred to as “seasoning”, which consists of adding a minimal amount of a biobased multifunctional monomer to pinch the amorphous domains of poly(butylene succinate). Seasoning with only 0.03 mol % of a biobased monomer led to a significantly improved oxygen barrier, high strength (86 MPa), and excellent elongation at break (654%). To the best of our knowledge, this “seasoning” approach with the significant property improvement provided is unique in the bioplastics research field. The proposed approach is highly scalable, relies on existing industrial production, and has the potential to expand current biodegradable plastic applications through its simplicity.
|
|
| 6. |
- Nordell, Patricia
(författare)
-
Aluminium oxide - poly(ethylene-co-butylacrylate) nanocomposites : synthesis, structure, transport properties and long-term performance
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Polymer nanocomposites are promising materials for dielectrical use in high voltage applications and insulations. This work presents a study of nanocomposites based on poly(ethylene-co-butyl acrylate) with two different comonomer compositions and two different aluminium oxide nanoparticles. The nanoparticles were either untreated, or surface-treated with two different silanes, aminopropyl triethoxy silane and octyltriethoxy silane. The best level of dispersion was found for the polymer with 13 wt. % of butyl acrylate (EBA-13) whereas the low melt viscosity of the polymer with 28 wt. % of butyl acrylate (EBA-28) resulted in insufficient mixing with uneven dispersion as a result. Octyltriethoxy silane-treated particles were best dispersed in the polymer. The nanoparticles acted as nucleation agents in EBA-28, increasing the crystallization temperature by several degrees. Studies of the water uptake in the nanocomposite materials showed the effect of the enormous interfacial surfaces and great number of polar groups present on the nanoparticle surfaces. For the well-dispersed nanomaterials, the water sorption data could be modeled by a single Fickian equation, whereas materials that contained a sizeable fraction of large nanoparticle agglomerates showed a two stage sorption process, first a fast process associated with the saturation of the polymer phase and second, a slow diffusion process due to water sorption of large particle agglomerates. The long-term performance and interaction between the nanoparticles and the phenolic antioxidant (Irganox 1010) was investigated by differential scanning calorimetry in order to assess the oxidation induction time (OIT); the latter being proportional to the concentration of efficient antioxidant. It was found that the stabilizer was adsorbed to the untreated Al2O3 nanoparticles, resulting in a significant reduction in OIT. However, silanization of the nanoparticles resulted in an increase in OIT, compared to the materials containing untreated particles. Furthermore, it was shown that the stabilizer was not irreversibly adsorbed to the particles, allowing a gradual release of stabilizer with ageing time.
|
|
| 7. |
|
|
| 8. |
- Yu, Wenbin
(författare)
-
Degradation of polyethylene pipes distributing chlorinated water : depletion of stabilizers, release of degraded products and polymer degradation
- 2011
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the study of antioxidants depletions in chlorinated media (10 ppm Cl2 - and ClO2 - aqueous media), polyethylene pipes degradations scenarios and migration of the degraded species to aqueous phase. Pressure testing on pipes and squalane testing with controlled pH aqueous media (6.8 ± 0.2) containing either Cl2 or ClO2 were used for assessing the degradation products. Though squalane test used a liquid hydrocarbon instead of real plastic, it provided reliable data with an efficient and readily way of sampling. Medium density polyethylene pipes stabilized with hindered phenol and phosphite antioxidants were pressure tested with water containing 4 ppm chlorine dioxide (ClO2) at 90 °C as internal medium. The stabilizers were rapidly consumed towards the inner pipe wall; the rate of consumption was four times greater than in chlorinated (Cl2) aqueous (4 ppm, pH = 6.8) at the same temperature. The depletion of stabilizers occurred far into the pipe wall. The subsequent polymer degradation was an immediate surface reaction. It was confirmed by differential scanning calorimetry, infrared spectroscopy and size exclusion chromatography that in the surface layer which came into contact with the oxidizing medium, the amorphous component of the polymer was heavily oxidized leaving a highly crystalline powder with many carboxylic acid chain ends in extended and once-folded chains. The depletion rate of the antioxidant exposed to ClO2 - aqueous media was also four times faster than that exposed to Cl2 - aqueous media by squalane test. The aqueous media was extracted to condense the remaining antioxidants and the degraded species from the squalane solution. The absorption spectra from infrared spectroscopy illustrated that carbonyl groups exist in degraded species from both ClO2 - and Cl2 - aqueous, and chlorine-carbon bond presented only in ClO2 - aqueous. It was proved by liquid chromatography that the peaks of oxidizing species formed in ClO2 aqueous media were more intense and they were different from the ones degraded compounds in Cl2.
|
|
