Sustainability assessments of bio-based polymers

Bio-based polymers have become feasible alternatives to traditional petroleum-based plastics. However, the factors that influence the sustainability of bio-based polymers are often unclear. This paper reviews published life cycle assessments (LCAs) and commonly used LCA databases that quantify the environmental sustainability of bio-based polymers and summarizes the range of findings reported within the literature. LCA is discussed as a means for quantifying environmental impacts for a product from its cradle, or raw materials extraction, to the grave, or end of life. The results of LCAs from existing databases as well as peer-reviewed literature allow for the comparison of environmental impacts. This review compares standard database results for three bio-based polymers, polylactic acid (PLA), polyhydroxyalkanoate (PHA), and thermoplastic starch (TPS) with five common petroleum derived polymers. The literature showed that biopolymers, coming out of a relatively new industry, exhibit similar impacts compared to petroleum-based plastics. The studies reviewed herein focused mainly on global warming potential (GWP) and fossil resource depletion while largely ignoring other environmental impacts, some of which result in environmental tradeoffs. The studies reviewed also varied greatly in the scope of their assessment. Studies that included the end of life (EOL) reported much higher GWP results than those that limited the scope to resin or granule production. Including EOL in the LCA provides more comprehensive results for biopolymers, but simultaneously introduces greater amounts of uncertainty and variability. Little life-cycle data is available on the impacts of different manners of disposal, thus it will be critical for future sustainability assessments of biopolymers to include accurate end of life impacts.     

Poly(lactic acid) Synthesis in Solution Polymerization

The step-growth polymerization of L-lactic acid in solution was studied in this work. In order to attain a polymer with high molecular weight, the water formed during the polymerization must be continuously removed. The use of organic solvents with high boiling point, drying agents and reduced pressure led to poly(lactic acid) (PLA) with high molecular weight, directly from the monomer. Tin (II) chloride dihydrate, SnCl₂.2H₂O, was the best of the catalysts tested as it allowed achieving PLA with a molecular weight close to 80 000 g.mol⁻¹. However, the stereoregurarity control is a severe problem in PLA synthesis by step-growth due to transesterification reactions, which lead to an inversion of the conformation and a decrease of the optical purity of the polymer. Specific rotation measurements were used in this work and showed to be a powerful technique to evaluate the racemization extent. The thermal stability of the PLA samples was evaluated by DSC which exhibits a thermal behaviour similar to the commercial Polylactide.     

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse ¹³C NMR spectra and spin-lattice relaxation times T₁(¹H), detected indirectly via ¹³C carbons, and T₁(¹³C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the ¹³C NMR lines and proton spin-lattice relaxation times T₁(¹H). The spin-lattice relaxation times T₁(¹³C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.     

聚乳酸/壳聚糖季铵盐皂石纳米复合材料的原位插层聚合及性能表征

通过两步法将2,3-环氧丙基三甲基氯化铵接枝壳聚糖合成了水溶性壳聚糖季铵盐(HTCC),以其为插层剂对稀有的新疆皂石(Saponite)黏土矿物进行有机改性,制备了壳聚糖季铵盐皂石(HTCC-saponite),并以其为助剂,以丙交酯为单体,通过原位插层聚合法制备了聚乳酸(PLA)/HTCC-saponite纳米复合材料.最优化合成条件:聚合反应温度150℃,辛酸亚锡加量2%(质量分数),HTCC-saponite加量1%(质量分数)、聚合反应时间16 h.微观结构分析表明HTCC-saponite具有插层与剥离共存的结构.采用X射线衍射(XRD)、透射电子显微镜(TEM)、热重分析(TG-DTG)和差示扫描量热仪(DSC)等对PLA/HTCC-saponite纳米复合材料的微观结构、形貌及热稳定性进行了表征和分析.结果表明,HTCC-saponite有效改善了PLA的结晶性能,提高PLA的热稳定性.抗菌测试结果表明,HTCC-saponite具有良好的抗菌性,并赋予PLA/HTCC-saponite复合材料较强的抑菌能力.     

表面微图案化聚乳酸膜的制备及其细胞亲和性评价

利用溶剂-非溶剂法(SNS)制备表面具有微孔图案的聚乳酸(PLA)膜和聚苯乙烯(PS)膜,并以微孔PS膜为模板,构建表面具有微岛图案的PLA膜.以此为基础,对所制备的微图案表面对PLA膜亲/疏水性及成骨细胞粘附与增殖性能的影响进行研究.结果显示微图案的存在显著增强了PLA膜的表面疏水性(水接触角90°);成骨细胞在微图案表面具有良好的铺展性,其黏附数量明显高于光滑PLA膜,但细胞的生长曲线相对较平缓,显示微图案表面虽有利于细胞在PLA膜表面的粘附与铺展,但对促进细胞的增殖无贡献.     

离子色谱法测定聚乳酸(PLA)降解产物中3种有机酸阴离子

为了建立聚乳酸(PLA)降解产物中3种有机小分子酸阴离子[CH3CH(OH)COO-,CH3CH2COO-,CH3COO-]的离子色谱检验方法,将PLA降解第5天的产物过滤后用离子色谱检测,色谱条件:淋洗液为NaHCO3(6.0mmol/L);流速为1.0mL/min;检测器为电导检测器。实验表明对乳酸、甲酸、乙酸标准曲线的线性相关系数在0.991以上,3种离子的相对标准偏差(RSD)在0.9%～3.7%。方法具有方便、准确、成本低的特点。     

Different enantioselectivity of two types of poly(lactic acid) depolymerases toward poly(l-lactic acid) and poly(d-lactic acid)

Poly(lactic acid) (PLA) depolymerases are categorized into protease-type and lipase-type. Protease-types can hydrolyze poly(l-lactic acid) (PLLA) but not poly(d-lactic acid) (PDLA). Lipase-types, including cutinase-like enzyme (CLE) from Cryptococcus sp. strain S-2 preferentially hydrolyze PDLA. Both enzymes degraded not only PLA emulsion but also PLA film, in which amorphous region is preferentially attacked, but crystalline region can be also attacked. Stereocomplex PLA (sc-PLA) formed by 50:50 blending of PLLA and PDLA included no homo crystals, but a tiny homo crystallization peak appeared and crystallinity increased by 5% when attacked by CLE, although no significant change of molecular weight and crystalline size was found. Enantioselective degradation must occur in amorphous region of PLLA/PDLA film and preferentially hydrolyzed PDLA, resulting in a slightly excess amount of PLLA remained, which must be crystallized.     

Microneedles-based electrochemical sensors: New tools for advanced biosensing

Electrochemical biosensors are used worldwide as analytical tools from laboratory applications to market products. The performance of electrochemical sensing can be boosted by adopting the microneedle (MN) geometry as an innovative configuration of standard electrodes. MNs can be miniaturized, easily functionalized, and properly designed for specific aim monitoring, but most of all, they allow a low invasive controlling tool for growth and for environment influence in plant and a painless door to human body fluids where target analytes can be detected, overcoming the natural barrier of the skin. In this review, the very recent developments in MN-based electrochemical biosensing published in the literature are summarized.     

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.     

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.