Multiple melting behavior of poly(lactic acid) filled with modified carbon black

Two melting peaks are generally observed in a heating scan for isothermally crystallized poly(lactic acid) (PLA)/carbon black (CB) and PLA/modified carbon black (MCB) composites. To investigate the origin of the above double melting behavior, the melting behavior after isothermal crystallization was analyzed with differential scanning calorimetry, wide‐angle X‐ray diffraction, and small angel X‐ray scattering techniques. The double melting of the crystallized samples can be explained by the model of two populations of lamellae, the double peaks of low and high temperatures are contributed to the melting of the small lamellae produced by secondary crystallization and that of the major crystals formed in the primary crystallization process, respectively. Spherulitic growth rates of the neat PLA and PLA/MCB composite were analyzed and the occurrence of a regime transition was demonstrated. For the PLA, a clear regime transition was observed at around 125 °C. For the PLA/MCB, it occurred at 130 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1971–1980, 2009     

Biomedical applications of biodegradable polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. To fit functional demand, materials with desired physical, chemical, biological, biomechanical, and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Effect of Phase Arrangement on Solid State Mechanical and Thermal Properties of Polyamide 6/Polylactide Based Co-polyester Blends

The main goal of this work is to correlate morphological parameters of the binary blend of polyamide 6 (PA6) and a polylactide (PLA) based biodegradable co-polyester blend (BioFlex) (scanning electron microscopy, solvent extraction method) with the solid-state mechanical properties (stress strain analysis) as well as thermal (differential scanning calorimetry) and selected physico-chemical characteristics (Fourier transform infrared spectroscopy and water uptake analysis). The blends of PA6/BioFlex were prepared in ratios of 100/0, 90/10, 75/25, 60/40, 50/50, 40/60, 25/75, 10/90 and 0/100 in wt.%. The occurrence of co-continuous morphology was observed within the range of 40 to 60 wt.% of BioFlex. Furthermore, the results show that the co-continuous morphology of PA6/BioFlex blends significantly affected both tensile (E modulus) and thermal properties (melting enthalpy) of the blends. In the case of the tensile properties, the effect of the morphological arrangement was strongly dependent on the deformation range. The presence of BioFlex in the blends reduced the crystallizability of PA6 noticeably. Co-continuous structure formation was observed to have a significant effect on the melting enthalpy of the blend. Composition morphology dependent responses were observed in the case of the FTIR and water uptake studies.     

Morphology of polylactic acid crystallized during annealing after uniaxial deformation

Uniaxial deformation of amorphous L -polylactic acid films was performed at two different temperatures at which thermal degradation was minimal, 70 °C or T_g + 10 and 90 °C or T_g + 30. Samples were annealed postdeformation for long times (either 15 or 45 min) to approach equilibrium conditions. Samples deformed and annealed at 70 °C showed low crystallinity and poor crystalline order or crystal size, as determined by wide-angle X-ray diffraction. At 90 °C, high crystallinity and order parameters were observed. In addition, once the oriented chains had crystallized at this temperature, nonoriented chains also underwent crystallization, and a small fraction of nonordered crystal phase was therefore observed after long annealing times. These observations are explained on the basis of different morphologies in samples drawn at the two temperatures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

New Insight into Biodegradation of Polylactide (PLA)/Clay Nanocomposites Using Molecular Ecological Techniques

Novel molecular ecological techniques were used to study changes in microbial community structure and population during degradation of polylactide (PLA)/organically modified layered silicates (OMLS) nanocomposites. Cloned gene sequences belonging to members of the phyla Actinobacteria and Ascomycota comprized the most dominant groups of microorganisms during biodegradation of PLA/OMLS nanocomposites. Due to their numerical abundance, members of these microbial groups are likely to play an important role during biodegradation process. This paper presents new insights into the biodegradability of PLA/OMLS nanocomposites and highlights the importance of using novel molecular ecological techniques for in situ identification of new microorganisms involved in biodegradation of polymeric materials.

     

Synthesis and hydrolysis behaviour of poly(ester anhydrides) from polylactone precursors containing alkenyl moieties

Hydroxyl-group functional polylactones were prepared and converted to acid- terminated polyesters in a reaction with a series of alkenylsuccinic anhydrides containing 8, 12, or 18 carbons in their alkenyl chains. These polyester precursors were then linked into higher molecular weight poly(ester anhydrides) containing alkenyl moieties in their polyester blocks. The hydrolysis behaviour of the poly(ester anhydrides) was found to depend on the thermal properties of the polyester precursors. For poly(ester anhydrides) prepared from low molecular weight prepolymers with thermal transitions below 37 degrees C, the presence of hydrophobic alkenyl chains in the polyester precursors slowed the rate of weight loss. Poly(ester anhydrides) prepared from higher molecular weight prepolymers showed the opposite weight-loss behaviour; i.e., the crystallinity and thermal transitions of the alkenyl chain-containing poly(ester anhydrides) were low, and the weight loss was faster than for poly(ester anhydrides) without the alkenyl chains. The differences in length of the alkenyl chain, as such, had little effect on the hydrolysis behaviour and thermal properties of the poly(ester anhydrides).     

聚己二酸甘油酯的合成及其对聚乳酸材料的增韧

以丙三醇、己二酸为原料,通过熔融缩聚合成了新型聚乳酸(PLA)增韧改性剂聚己二酸丙三醇酯(PGA).利用傅立叶变换红外光谱(FT-IR),核磁共振氢谱(1H-NMR)及凝胶渗透色谱(GPC)等方法对不同反应温度条件下PGA的分子结构进行了表征.同时通过熔融共混制备了PGA/PLA共混物,并测试了共混物的冲击性能,利用差示扫描量热仪(DSC)和扫描电子显微镜(SEM)对其热性能及相形貌进行了表征.结果表明:PGA可以有效增韧聚乳酸,160℃下合成的PGA增韧性最佳,冲击强度达到48.0 J/m,较纯聚乳酸提高了3倍.PGA分子支化结构的差异对PGA/PIA的共混形态有明显的影响,从而进一步影响其增韧效果.     

Synthesis and characterization of novel biodegradable block copolymer poly(ethylene glycol)‐block‐poly(L‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylene carbonate)

An amphiphilic block copolymer, poly(ethylene glycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate) [PEG‐b‐P(LA‐co‐MBC)], was synthesized in bulk by the ring‐opening polymerization of L ‐lactide with 2‐methyl‐2‐benzoxycarbonyl‐propylene carbonate (MBC) in the presence of poly(ethylene glycol) as a macroinitiator with diethyl zinc as a catalyst. The subsequent catalytic hydrogenation of PEG‐b‐P(LA‐co‐MBC) with palladium hydroxide on activated charcoal (20%) as a catalyst was carried out to obtain the corresponding linear copolymer poly(ethyleneglycol)‐block‐poly(L ‐lactide‐co‐2‐methyl‐2‐carboxyl‐propylenecarbonate) [PEG‐b‐P(LA‐co‐MCC)] with pendant carboxyl groups. DSC analysis indicated that the glass‐transition temperature (T_g) of PEG‐b‐P(LA‐co‐MBC) decreased with increasing MBC content in the copolymer, and T_g of PEG‐b‐P(LA‐co‐MCC) was higher than that of the corresponding PEG‐b‐P(LA‐co‐MBC). The in vitro degradation rate of PEG‐b‐P(LA‐co‐MCC) in the presence of proteinase K was faster than that of PEG‐b‐P(LA‐co‐MBC), and the cytotoxicity of PEG‐b‐P(LA‐co‐MCC) to chondrocytes from human fetal arthrosis was lower than that of poly(L ‐lactide). © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4771–4780, 2005     

Characteristic properties of film prepared from poly(L‐lactide)‐grafted dextran of a relatively high sugar unit content as a degradable biomaterial

To develop novel biomedical soft materials with degradability, amphiphilic poly(L ‐lactide)‐grafted dextrans (Dex‐g‐PLLAs) of relatively high sugar unit contents were synthesized with the trimethylsilyl protection method. The characteristic properties of solution‐cast films prepared from the obtained Dex‐g‐PLLAs were investigated. The water absorption and degradation rate of the Dex‐g‐PLLA films increased with increasing sugar unit content. The morphology of the bulk phase and top surface of the Dex‐g‐PLLA films was evaluated with transmission electron microscopy and atomic force microscopy, respectively. The bulk phase of the Dex‐g‐PLLA films with a sugar unit content of 16–25 wt % was found by transmission electron microscopy to form a lamellar type of phase‐separated structure composed of approximately 80–100‐nm‐wide nanodomains because of their amphiphilic and branched structures. The hydrophobic top surface for a Dex‐g‐PLLA film with a sugar unit content of 25 wt % covered with PLLA segments was confirmed by atomic force microscopy phase images to be easily converted to a wettable top surface covered with hydrophilic dextran aggregates showing an 8–10‐nm‐wide honeycomb pattern by means of annealing in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6402–6409, 2006