| 1. |
- Burman, Lina, et al.
(author)
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Chromatographic Fingerprinting - a Tool for Classification and for Predicting the Degradation State of Degradable Polyethylene
- 2005
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In: Polymer degradation and stability. - : Elsevier BV. - 0141-3910 .- 1873-2321. ; 89:1, s. 50-63
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Journal article (peer-reviewed)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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| 2. |
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| 3. |
- Guo, Baolin, et al.
(author)
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Degradable and Electroactive Hydrogels with Tunable Electrical Conductivity and Swelling Behavior
- 2011
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In: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 23:5, s. 1254-1262
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Journal article (peer-reviewed)abstract
- Degradable electrically conducting hydrogels (DECHs), which combine the unique properties of degradable polymers and electrically conducting hydrogels, were synthesized by introducing biodegradable segments into conductive hydrogels. These DECHs were obtained by joining together the photopolymerized macromer acrylated poly(D,L-lactide)-poly(ethylene glycol)-poly(D,L-lactide) (AC-PLA-PEG-PLA-AC), glycidyl methacrylate (GMA), ethylene glycol dimethacrylate (EGDMA) network and aniline tetramer (AT) by the coupling reaction between AT and the GMA The electrical conductivity and swelling behavior of these DECHs were tuned by changing the AT content in the hydrogels, the cross-linking degree, and the environmental pH value. The good electroactivity and thermal stability of these hydrogels were demonstrated by UV-vis spectroscopy, cyclic voltammetry, and TGA tests. The chemical structure and morphology of these polymers were characterized by NMR, FT-IR, SEC, and SEM. These hydrogels possessing both degradability and electrical conductivity represent a new class of biomaterial and will lead to various new possibilities in biomedical applications.
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| 4. |
- Guo, Baolin, et al.
(author)
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Universal Two-Step Approach to Degradable and Electroactive Block Copolymers and Networks from Combined Ring-Opening Polymerization and Post-Functionalization via Oxidative Coupling Reactions
- 2011
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 44:13, s. 5227-5236
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Journal article (peer-reviewed)abstract
- We present a universal strategy for the facile synthesis of degradable and electroactive block copolymers and organogels (DEBCGs) based on aniline oligomers and polyesters in a two-step approach, here exemplified by the preparation of a series of DECBCGs based on aniline tetramer (AT) and poly(e-caprolactone) (PCL). Polyesters with an aniline dimer (AD) segment were first obtained by controlled ring-opening polymerization (ROP) of e-caprolactone initiated by the amine group of AD with or without 2,2-bis(epsilon-caprolactone-4-yl) propane (BCP). The postpolymerization modification via an oxidative coupling reaction between AD and a polyester was then used to form the electroactive segment AT in the copolymers or organogels. The molecular weight and conductivity of the block copolymers and organogels were controlled by the AT content. The chemical structure, electroactivity, and thermal properties of DEBCGs were investigated by FT-IR, NMR, SEC, UV, cyclic voltammetry, TGA, and DSC. Our general strategy for the synthesis of DECBCGs avoids the multiple step reactions and low efficiency involved in previous work.
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| 5. |
- Målberg, Sofia, et al.
(author)
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Macromolecular Design of Aliphatic Polyesters with Maintained Mechanical Properties and a Rapid, Customized Degradation Profile
- 2011
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 12:6, s. 2382-2388
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Journal article (peer-reviewed)abstract
- An innovative type of triblock copolymer that maintains and even increases the mechanical properties of poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) with a controlled, predictable, and rapid degradation profile has been synthesized. Elastic triblock copolymers were formed from the hydrophobic and crystalline PLLA and PCL with an amorphous and hydrophilic middle block of poly(but-2-ene-1,4-diyl malonate) (PBM). The polymers were subjected to degradation in PBS at 37 degrees C for up to 91 days. Prior to degradation, ductility of the PLLA-PBM-PLLA was approximately 4 times greater than that of the homopolymer of PLLA, whereas the modulus and tensile stress at break were unchanged. A rapid initial hydrolysis in the amorphous PBM middle block changed the microstructure from triblock to diblock with a significant reduction in ductility and molecular weight. The macromolecular structure of the triblock copolymer of PLLA and PBM generates a more flexible and easier material to handle during implant, with the advantage of a customized degradation profile, demonstrating its potential use in future biomedical applications.
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| 6. |
- Plikk, Peter, 1978-
(author)
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Porous degradable polyester scaffolds
- 2006
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Licentiate thesis (other academic/artistic)abstract
- Tissue engineering is a growing research field in which degradable porous scaffolds are used to regenerate tissue from the patients own cells. The problems due to donor shortage or the lack of full property restoration from prosthetic implants can thereby be overcome. It is important that the polymers used in tissue engineering, as in any medical application, have well controlled properties. Equally important is the ability to tailor these properties to suite a specific application. The development of fabrication processes that enables tailoring, without any uncontrolled changes in characteristics, is thereby imperative. In this thesis, the creation of porous scaffolds focusing on tailoring and customizing the scaffold properties is described. Tailoring was achieved by selecting the proper monomers and their compositions when copolymerizing different cyclic aliphatic ester monomers and an ether-ester monomer. Porous structures applicable for both soft and hard tissue regeneration were obtained comprising a range of predetermined mechanical and thermal properties. In detail, stannous octoate was used as the catalyst in ring-opening polymerization of L,L-lactide (LLA), ε-caprolactone (CL) and 1,5-dioxepane-2-one (DXO) to attain the wide assortment of copolymers with different monomers and monomer compositions. Highly porous scaffolds having well interconnected pores were obtained through the development of a versatile solvent casting and porogen leaching technique. The reactions induced by high energy radiation in the form of electron beam and gamma-ray were used to finalize the scaffold properties. This was achieved by creating polymers possessing predetermined reaction mechanisms when irradiated. Changes in the nature of the radiation, the radiation dose, the type of monomers, the composition and thus the microstructure of the chain gave ways to alter the susceptibility and the reaction mechanism of the polymers. Thus, predicted end-products are obtainable and the sterilization procedure is consequently incorporated as a final step in the scaffold fabrication.
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| 7. |
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| 8. |
- Strandberg, Clara, et al.
(author)
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Improvement of α-tocopherol’s Long-Term Efficiency by Modeling Its Heterogeneous Natural Environment in Polyethylene
- 2006
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In: Journal of Polymer Science Part A. - : Wiley. - 0887-624X .- 1099-0518. ; 44:5, s. 1660-1666
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Journal article (peer-reviewed)abstract
- The natural antioxidant vitamin E (α-tocopherol) is of interest to use in packaging applications to decrease the amount of toxic products migrating into food and drugs. We have earlier shown that the long-term efficiency of α-tocopherol in polyethylene (PE) films is poor. α-Tocopherol is located in the lipid phase of the cell in vivo and it has been revealed that it is more efficient in a polar substrate. PE is more hydrophobic and homogenous than the heterogeneous and hydrophilic lipid phase. Three different additive systems were investigated to model α-tocopherols heterogeneous natural environment in PE. Two of these had carboxylic acid groups, EAA and polyTRIM/PAA core-shell particles (Core), and the third, oat starch, had no carboxylic acid groups. The materials were thermally aged and characterized by chemiluminescence (CL), FTIR, chromatography, and thermal analysis. The EAA system as well as the Core system improved the antioxidant properties of α-tocopherol in PE, and the Core system had the best performance. We know that starch has stabilizing properties in PE, but it had no effect on the efficiency of α-tocopherol.
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| 9. |
- Strandberg, Clara, 1975-
(author)
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Long-term properties of polyethylene films : efficiency of a natural antioxidant
- 2006
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Doctoral thesis (other academic/artistic)abstract
- There is a growing awareness of the risks of pollution in biological systems and one potential problem is the synthetic antioxidants, used for e.g. the stabilisation of polymeric materials. Natural antioxidants are an interesting alternative, if the high efficiency and thermal stability of the synthetic compounds can be reached. In the work described in this thesis, vitamin E (alfa-tocopherol) was studied as a natural antioxidant for the stabilisation of one of the major plastics, polyethylene (PE). The dependence of the surrounding environment for the efficiency of alfa-tocopherol in polyethylene (PE), throughout thermal aging, was characterised by sensitive techniques. Two techniques which have shown a high sensitivity in oxidation detection of polymers; chemiluminescence (CL) and gas chromatographic analysis, were compared with the commonly used methods, infrared spectroscopy (FT-IR) and thermal analysis. Three different additive systems were selected as active domains for -tocopherol in PE. Two of these contained carboxylic acid groups, poly (ethylene-co-acrylic acid) (EAA) and polyTRIM/PAA core-shell particles (Core), and the third, oat starch, had no such groups. The additives containing carboxylic groups improved the long-term efficiency of alfa-tocopherol in PE, according to carbonyl index measurements made by FT-IR, while the additive without carboxylic acid groups gave no improvement. The amount of carboxylic acids emitted from the materials after thermal aging, assessed by head-space solid-phase microextraction (HS-SPME) and gas chromatography-mass spectroscopy (GC-MS), also showed that EAA increased the antioxidant efficiency of alfa-tocopherol, whereas the Core system showed lower antioxidant efficiency. Reference systems containing the synthetic antioxidant Irganox 1076 and EAA or oat starch had the same performance as the materials stabilised with only the antioxidants. CL measurements in an inert atmosphere (TLI) have earlier been shown to give earlier oxidation detection than carbonyl index measurements in unstabilised PE. In this work, the TLI analysis and the carbonyl index measurements had the same sensitivity in the detection of oxidation in the stabilised materials. Assessment of low-molecular weight carboxylic acids in PE during the aging was made by gas chromatographic analysis together with solid-phase extraction. Propanoic acid showed the best correlation with the carbonyl index measurements, even if the carbonyl index showed earlier detection of oxidation. It was also found that TLI and CL in an oxidative atmosphere (CL-OIT) had the same sensitivity and were in accordance for all of the materials, with exception of the materials containing EAA and alfa-tocopherol or Irganox 1076. CL-OIT was also compared to the oxygen induction time determined by thermal analysis.
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| 10. |
- Strandberg, Clara, et al.
(author)
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Process Efficiency and Long-Term Performance of alpha-tocopherol in Film-Blown Linear Low-Density Polyethylene
- 2005
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In: Journal of Applied Polymer Science. - : Wiley. - 0021-8995 .- 1097-4628. ; 98, s. 2427-2439
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Journal article (peer-reviewed)abstract
- Alpha-Tocopherol was compared with a commercial phenolic antioxidant (Irganox 1076) as a long-term and process antioxidant in film-blown and compression-molded linear low-density polyethylene. The antioxiclant function of alpha-tocopherol was high in the film-blown material, especially in the processing, according to oxygen induction time measurements with differential scanning calorimetry. The residual content of alpha-tocopherol after processing, determined with chromatographic techniques, was less than that of the commercial phenolic antioxidant in both the film-blown and compression-molded materials. The process stabilizing efficiency was nevertheless higher for the material containing alpha-tocopherol. During the long-term stabilization, the efficiency of alpha-tocopherol was less than that of the commercial phenolic stabilizer Irganox 1076 in the thin films, according to chemiluminescence and infrared measurements. The long-term efficiency in the compression-molded samples stabilized with alpha-tocopherol or Irganox 1076 was equally good because of the low loss of both alpha-tocopherol and Irganox 1076 from the thicker films
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