| 1. |
- Oksman, Kristiina, et al.
(författare)
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Influence of thermoplastic elastomers on adhesion in polyethylene-wood flour composites
- 1998
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 68:11, s. 1845-1855
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of recycled low-density polyethylene/wood flour (LDPE/WF) composites are improved when a maleated triblock copolymer styrene-ethylene/butylene-styrene (SEBS-MA) is added as a compatibilizer. The composites' tensile strength reached a maximum level with 4 wt % SEBS-MA content. The compatibilizer had a positive effect on the impact strength and elongation at break but decreased the composites' stiffness. Dynamic mechanical thermal analysis (DMTA), a lap shear adhesion test, and a scanning electron microscope (SEM) were used to investigate the nature of the interfacial adhesion between the WF/SEBS and between the WF/ SEBS-MA. Tan δ peak temperatures for the various combinations showed interaction between the ethylene/butylene (EB) part of the copolymer and the wood flour in the maleated system. The shear lap test showed that adhesion between the wood and SEBS-MA is better than between the wood and SEBS. The electron microscopy study of the fracture surfaces confirmed good adhesion between the wood particles and the LDPE/SEBS-MA matrix. © 1998 John Wiley & Sons, Inc.
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| 2. |
- 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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| 3. |
- Karlsson, A., et al.
(författare)
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A new method for the determination of a hydrosilanization inhibitor applied to measurements during curing of a silicone elastomer
- 2001
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 79:13, s. 2349-2353
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Tidskriftsartikel (refereegranskat)abstract
- A new method for the quantitative determination of the hydrosilylation inhibitor 1-ethynyl-1-cyclohexanol in a poly(dimethyl siloxane) matrix is presented. The method is based on headspace gas chromatography directly from the semisolid sample without solvent addition. The method was found to be both selective and sensitive. The relative standard deviation of the method was estimated to be 6%. The semisolid silicone sample was weighed directly in a headspace autosampler vial. After sample equilibration at 90 degreesC for 1 h, the gas phase was injected into a gas chromatography system with a nonpolar methyl silicone capillary column. The inhibitor was detected with a flame ionization detector. The standard addition procedure was used for quantification. Recovery data on the inhibitor from the silicone during curing suggests that the inhibitor reacts with the silicone hydride crosslinker in the presence of the platinum catalyst to become part of the polymer network. This implies that the inhibitor will not migrate out from the silicone elastomer, which is a great advantage particularly for silicone elastomers used for medical devices or controlled drug release applications.
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| 4. |
- Khabbaz, F., et al.
(författare)
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Py-GC/MS an effective technique to characterizing of degradation mechanism of poly (L-lactide) in the different environment
- 2000
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 78:13, s. 2369-2378
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Tidskriftsartikel (refereegranskat)abstract
- The biotic and abiotic degradation of poly (L-lactide) (PLLA) has been studied with pyrolysis gas chromatography mass spectrometry (Py-GC-MS). A mixed culture of compost micro-organisms was used as the biotic medium. Size-exclusion chromatography (SEC), gas chromatography-mass spectrometry (GC-MS), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) were utilized to monitor the degradation and degradation mechanism. Differences in pH, molecular weight, surface structure, and degradation mechanisms were noted between sample aged in biotic and abiotic medium. Using fractionated Py-GC-MS at 400 and 500 degreesC, acetaldehyde, acrylic acid, lactoyl acrylic acid, two lactide isomers, and cyclic oligomers up to the pentamer were identified as thermal decomposition products of PLA as well as some other not completely identified products. The ratio of meso-lactide to L-lactide was lower in the sample aged in the biotic media than the abiotic media. This is a result of the preference of the micro-organisms for L-form of lactic acid and lactoyl lactic acid rather than the D-form that in turn influences the formation and the amounts of meso and D,L-lactide during the pyrolysis. Based on SEM micrographs, it was shown that degradation in the biotic medium proceeded mainly via a surface erosion mechanism, whereas bulk erosion was the predominant degradation mechanism in the abiotic medium. The SEC and Py-GC-MS data indicate that degradation was faster in the biotic than in the abiotic sample.
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| 5. |
- Khabbaz, F., et al.
(författare)
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Rapid test methods for analyzing degradable polyolefins with a pro-oxidant system
- 2001
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 79:12, s. 2309-2316
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Tidskriftsartikel (refereegranskat)abstract
- Chemiluminescence, size exclusion chromatography, differential scanning calorimetry, thermogravimetry, and Fourier transform infrared spectroscopy were used to assess differences in oxidation rate between two different pro-oxidant systems in degradable low-density polyethylene. The pro-oxidant formulation used consisted of manganese stearate and natural rubber or manganese stearate and a synthetic, styrene-butadiene copolymer rubber. The low-density polyethylene containing the prooxidant with natural rubber showed the highest degradation rate. Chemiluminescence and thermogravimetry were found to be the most effective techniques for establishing the differences between different pro-oxidant systems.
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| 6. |
- Edlund, Ulrica, et al.
(författare)
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Copolymerization and polymer blending of trimethylene carbonate and adipic anhydride for tailored drug delivery
- 1999
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 72:2, s. 227-239
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Tidskriftsartikel (refereegranskat)abstract
- The copolymerization in bulk and solution of trimethylene carbonate (TMC) with adipic anhydride (AA) as well as the blending of homopolymers are described. We show experimentally that the components are not copolymerizable but partially miscible, forming a microscopic dispersion without any visible signs of phase separation. Poly(adipic anhydride) (PAA) functions as a plasticizer, permitting an increase in the erosion rate by increasing the porosity and hydration. Drug delivery from the blends was evaluated. A statistical factorial model was designed to explore the influence of three important blend parameters and their interactions, making it possible to predict the erosion and drug-release behavior of the blend matrices. The PAA:poly(trimethylene carbonate) (PTMC) ratio and molecular weight of the polycarbonate component significantly influence the drug-release performance, mass loss, and degree of plasticization. The interaction among these factors also influences the blend properties. Plasticization of PTMC enhances the drug release to an extent that is dependent on the amount of PAA used. We demonstrate that blending offers a convenient alternative to copolymerization for the preparation of polymer matrices with predictable drug delivery.
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| 7. |
- Gamstedt, E. Kristofer
(författare)
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Effects of debonding and fiber strength distribution on fatigue-damage propagation in carbon fiber-reinforced epoxy
- 2000
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 76:4, s. 457-474
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Tidskriftsartikel (refereegranskat)abstract
- In order to design new fatigue-resistant composites, the underlying fatigue damage mechanisms must be characterized and the controlling microstructural properties should be identified. The fatigue-damage mechanisms of a unidirectional carbon fiber-reinforced epoxy has been studied under tension-tension loading. A ubiquitous form of damage was one or a few planar fiber breaks from which debonds or shear yield zones grew in the longitudinal direction during fatigue cycling. This leads to a change in stress profile of the neighboring fibers, and an increase in failure probability of these fibers. The breakage of fibers in the composite is controlled by the fiber strength distribution. The interaction between the fiber strength distribution and debond propagation leading to further fiber breakage was investigated by a numerical simulation. It was found that a wider distribution of fiber strength and a higher debond rate lead to more distributed damage and a higher fracture toughness. Implications to fatigue life behavior are discussed, with reference to constituent microstructure.
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| 8. |
- Hakkarainen, Minna, et al.
(författare)
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Influence of low molecular weight lactic acid derivatives on degradability of polylactide
- 2000
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 76:2, s. 228-239
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Tidskriftsartikel (refereegranskat)abstract
- The presence of low molecular weight lactic acid derivatives in films enhanced the degradability of polylactide in a biotic medium. Two different biotic and abiotic series were investigated. The films used for the first abiotic and biotic series (a-l and b-1 films) initially contained some lactic acid and lactoyl lactic acid, while the films used for the second abiotic and biotic series (a-2 and b-2 films) did not originally contain them. The b-1 films decreased in molecular weight during 3 weeks in the biotic medium, while no molecular weight decrease was seen in the a-1 films aged in a corresponding abiotic mineral medium. The molecular weight for the a-2 and b-2 films without lactic and lactoyl lactic acid remained almost constant. Scanning electron microscopy micro-graphs showed a larger amount of bacteria and fungi growing on the surface of b-1 films compared to b-2 films; thus, the presence of easily assimilated lactic acid and lactoyl lactic acid in the films improved the initial growth of microorganisms on the film surfaces. Gas chromatography and mass spectrometry analysis showed that lactic acid and lactoyl lactic acid were rapidly assimilated from the films aged in a biotic medium. New degradation products (e.g., ethyl ester of lactoyl lactic acid, acetic acid, and propanoic acid) were formed during aging in a biotic medium. Acetic acid and propanoic acid were formed as intermediate degradation products during the initial stages, but they were no longer detected after prolonged aging. The concentration of the ethyl ester of lactoyl lactic acid increased with aging time.
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| 9. |
- Johansson, Mats K. G., et al.
(författare)
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Radiation curing of hyperbranched polyester resins
- 2000
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 75:5, s. 612-618
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Tidskriftsartikel (refereegranskat)abstract
- A research area that has obtained increasing interest during the last decade concerns improvement of macromolecular properties by changes in the macromolecular architecture. One group of these materials is dendritic polymers, which are highly branched structures exhibiting very different properties compared with linear polymers. One potential application for these polymers is as radiation curable thermoset resins. This article describes a study where the use of an aliphatic hyperbranched polyester as a base for new radiation curable thermoset resins. The hyperbranched polyesters have been characterized with respect to cure rate and final mechanical properties compared with conventional resins. It is shown that hyperbranched polyesters can be used as versatile scaffolds for various radiation curable resin structures.
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| 10. |
- Lindhagen, Johan, et al.
(författare)
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Microscopical damage mechanisms in glass fiber reinforced polypropylene
- 1998
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Ingår i: Journal of Applied Polymer Science. - 0021-8995 .- 1097-4628. ; 69:7, s. 1319-1327
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Tidskriftsartikel (refereegranskat)abstract
- The damage mechanisms in two structurally different glass mat reinforced polypropylene materials were studied. In situ microscopy was applied during the tensile testing of thin notched sheets. Micrographs of the damage processes in the two materials are presented. The major points of damage initiation were transversely oriented fibers and fiber bundles. In the swirled mat material, cracks grew along the fiber bundles; crack formation and growth was relatively unaffected by macroscopical stress concentration. In the short fiber material, crack growth occurred at the notch. In both materials the maximum load was determined by the fibers oriented in the longitudinal direction. The different damage mechanisms were interpreted in terms of damage zone size
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