Foaming and Damping Properties of Ethylene Vinyl-Acetate Copolymer/Polylactic Acid Blends

With ethylene vinyl-acetate copolymer (EVM) and polylactic acid (PLA) blends as the matrix, dicumyl peroxide (DCP) as the curing agent and azodicarbonamide (AC) as the foaming agent, EVM/PLA foamed blends were prepared by compression molding. The effects of different amounts of AC, DCP, and silica, as well as varying foaming time, on the cell structure and damping properties of the EVM/PLA-foamed blends were examined by scanning election microscopy (SEM) and dynamic mechanical analysis (DMA). The results showed that the cell size and damping properties varied little with increasing AC content in the compounds; however, the cell size declined slightly as DCP increased and the damping properties rose slightly, exhibiting an optimum set of properties at 5 phr of DCP. The cell size declined dramatically and damping increased significantly as the foaming time was increased. Moreover, both suddenly increased after 5 min foaming. It was found that the damping properties of the foamed materials increased with decreasing cell size and increasing number of cells. The cell size also decreased and damping properties increased as the silica content was increased. The silica interacted more strongly with EVM than with PLA.     

Molecular Dynamic Evaluation of starch-PLA blends nanocomposite with organoclay by proton NMR relaxometry

Starch and PLA were used alone and in blends to prepare nanostructured materials using both hydrophilic and organophilic clays, and PVA. All nanostructured materials were obtained by the solution intercalation method using water and chloroform as solvents. These systems were characterized by using conventional X-ray diffraction (XRD), conventional NMR and the non-conventional fast field cycling (FFC) NMR technique. The spin-lattice relaxation times were measured as a function of the Larmor frequency. The FFC results showed that the starch has only one relaxation time related to the amorphous region. PLA hybrids presented two distinct spin-lattice relaxation times. The blends of the two polymers also showed two relaxation times. The renormalized Rouse formalism was applied to describe the polymer molecular dynamics behavior in the studied systems containing starch. By adding clay or PVA, differences could be observed in relaxation time corresponding to the more amorphous region, indicating that, when adding clay and PVA, the effect that each has on the dynamics of the mixture is cancelled out.     

Synthesis of amphiphilic block copolymers via ring opening polymerization and reversible addition-fragmentation chain transfer polymerization

Amphiphilic block copolymers were synthesized via a dual initiator chain transfer agent (inifer) that successfully initiated the ring opening polymerization (ROP) of l -lactide (LLA) and subsequently mediated the reversible addition-fragmentation chain transfer (RAFT) polymerization of poly(ethylene glycol) ethyl ether methacrylate (PEGEEMA). The formation of each polymer block was confirmed using ¹H nuclear magnetic resonance spectroscopy, as well as gel permeation chromatography, and comprehensive kinetics studies provide valuable insights into the factors influencing the synthesis of well-defined block copolymers. The effect of monomer concentration, reaction time, and molar ratios of inifer to catalyst on the ROP of LLA are discussed, as well as the ability to produce poly(lactide) blocks of different molecular weights. The synthesis of hydrophilic PPEGEEMA blocks was also monitored via kinetics to provide a better understanding of the role the chain transfer agent plays in facilitating the complex and sterically demanding RAFT polymerization of PEGEEMA.     

New Polylactic Acid Composites for Packaging Applications: Mechanical Properties,Thermal Behavior,and Antimicrobial Activity

The interest in antimicrobial packaging materials based on polylactic acid (PLA) polymers has increased due to the need to improve food safety and environment quality and also to find alternatives to synthetic polymers made from petrochemicals. PLA films by addition of different fillers (grape wastes and celery fibers) were obtained. The mechanical, thermal, surface, and antimicrobial properties of the films were evaluated. The incorporation of inexpensive fillers into the PLA matrix could reduce costs and the studied formulations offer approaches to realize composites with high performances and antimicrobial response, suitable for film food-active packaging materials, especially by use of grape wastes.     

Poly(lactic acid)/(styrene‐ethylene‐butylene‐styrene)‐g‐maleic anhydride copolymer/sepiolite nanocomposites: Investigation of thermo‐mechanical and morphological properties

In this study, sepiolite nanoclay is used as reinforcing agent for poly(lactic acid) (PLA)/(styrene‐ethylene‐butylene‐styrene)‐g‐maleic anhydride copolymer (SEBS‐g‐MA) 90/10 (w/w) blend. Effects of sepiolite on thermal behavior, morphology, and thermomechanical properties of PLA/SEBS‐g‐MA blend were investigated. Differential scanning calorimetry results showed 7% improvement in crystallinity at 0.5 wt% of sepiolite. The nanocomposite exhibited approximately 36% increase in the tensile modulus and 17% increase in toughness as compared with the blend matrix at 0.5 and 2.5 wt% of sepiolite respectively. Field emission scanning electron microscopy and transmission electron microscopy images exhibited sepiolite‐induced morphological changes and dispersion of sepiolite in both PLA and SEBS‐g‐MA phases. Dynamic mechanical analysis and wide angle X‐ray diffraction present evidences in support of the reinforcing nature of sepiolite and phase interaction between the filler and the matrix. This study confirms that sepiolite can improve tensile modulus and toughness of PLA/SEBS‐g‐MA blend.     

Phospholipidomic identification of potential plasma biomarkers associated with type 2 diabetes mellitus and diabetic nephropathy

Type 2 diabetes mellitus (T2DM) and its attendant complications, such as diabetic nephropathy (DN), impose a significant societal and economic burden. The investigation of discovering potential biomarkers for T2DM and DN will facilitate the prediction and prevention of diabetes. Phospholipids (PLs) and their metabolisms are closely allied to nosogenesis and aggravation of T2DM and DN. The aim of this study is to characterize the human plasma phospholipids in T2DM and DN to identify potential biomarkers of T2DM and DN. Normal phase liquid chromatography coupled with time of flight mass spectrometry (NPLC-TOF/MS) was applied to the plasma phospholipids metabolic profiling of T2DM and DN. The plasma samples from control (n = 30), T2DM subjects (n = 30), and DN subjects (n = 52) were collected and analyzed. The significant difference in metabolic profiling was observed between healthy control group and DM group as well as between control group and DN group by the help of partial least squares discriminant analysis (PLS-DA). PLS-DA and one-way analysis of variance (ANOVA) were successfully used to screen out potential biomarkers from complex mass spectrometry data. The identification of molecular components of potential biomarkers was performed on Ion trap-MS/MS. An external standard method was applied to quantitative analysis of potential biomarkers. As a result, 18 compounds in 7 PL classes with significant regulation in patients compared with healthy controls were regarded as potential biomarkers for T2DM or DN. Among them, 3 DM-specific biomarkers, 8 DN-specific biomarkers and 7 common biomarkers to DM and DN were identified. Ultimately, 2 novel biomarkers, i.e., PI C18:0/22:6 and SM dC18:0/20:2, can be used to discriminate healthy individuals, T2DM cases and DN cases from each other group.     

直接法共聚改性聚乳酸研究新进展

聚乳酸(PLA)是一种重要的生物降解材料.广泛应用于生物医学、纤维、塑料等领域.为了改善PLA的性能,人们进行了大量的共聚改性研究.其中,直接从乳酸出发不经丙交酯中间体路线的共聚改性方法,因其简单易行、经济实用,越来越引起科学家的重视.针对直接法共聚改性聚乳酸物中物质种类的不同,结合本课题组的一些乳酸直接熔融共聚研究工...     

Structure,properties and interfacial interactions in poly(lactic acid)/polyurethane blends prepared by reactive processing

Polyurethane elastomers are promising candidates for the impact modification of PLA producing blends for example for biomedicine. Poly(lactic acid) (PLA)/polyurethane elastomer (PU) blends were prepared by reactive processing and physical blending as comparison. The blends were characterized by a number of techniques including microscopy (scanning electron microscopy, SEM, and atomic force microscopy, AFM), rotational viscometry, thermal (dynamic mechanical analysis, DMA), and mechanical (tensile) measurements. The analysis and comparison of the structure and properties of physical and reactor blends proved the successful coupling of the phases. Coupling resulted in more advantageous structure and superior mechanical properties compared to those of physical blends as confirmed by morphology, macroscopic properties and the quantitative estimation of interfacial interactions. Structural studies and the composition dependence of properties indicated the formation of a submicron, phase-in-phase structure which positively influenced properties at large PU contents. The results strongly support that reactive processing is a convenient, cost-effective and environmentally friendly technique to obtain blends with superior properties.     

采用固体NMR研究MPEG-PLA双嵌段共聚物的固态相区结构

采用固体核磁共振方法，研究了AB型聚（L-丙氨酸）聚乙二醇嵌段共聚物(MPEG-b-PLA）的固态微相结构. ¹³C核的交叉极化与直接极化实验表明，MPEG中存在晶态和非晶态两种相区结构，PLA则含有大量的α螺旋与少量的β折叠二级结构. 由交叉极化过程下的¹³C自旋-晶格弛豫时间(T₁)测定结果进一步表明，MPEG链段由于嵌段结构使结晶过程受抑制，结晶度明显下降. PLA链段以结晶态形式存在，并由于大量α螺旋和β折叠有序结构的存在, 链段非常刚性，运动严重受限，而β位甲基因为可以自由旋转，所以运动能力较α位次甲基和羰基强.