A Novel Synthetic Approach to Stereo-Block Poly(lactic acid)

Stereoblock poly(lactic acid) (sb-PLA), consisting of poly(L-lactic acid) (PLLA) and poly(D-lactic acid) (PDLA) in a blocky sequence, can successfully be synthesized by solid-state polycondensation of a stereocomplexed mixture of PLLA and PDLA. First, the melt polyconden-sation of L- and D-lactic acids is conducted to obtain PLLA and PDLA with medium molecular weights. Then, both polymers are melt-blended to easily form the stereocomplex. The resulting stereocomplexed mixture (melt-blend) is subjected to solid-state polycondensation for chain extension. The molecular weight (M_w) of the resultant sb-PLA is strongly affected by the lactide/oligomer content in the melt-blend, which is determined by the melt-blending conditions, because it is directly correlated with the polymer crystallinity of the polycondensation products.     

开环聚合-固相缩聚法制备立体嵌段聚乳酸

首先,采用乳酸为引发剂,辛酸亚锡为催化剂,引发丙交酯开环聚合制得具有缩聚活性的L-聚乳酸和D-聚乳酸;然后,将两者熔融共混后进行固相缩聚,合成了一系列立体嵌段聚乳酸。采用核磁共振(NMR)、凝胶渗透色谱(GPC)及差示扫描量热仪(DSC)分析了产物的链结构、重均分子量、热性能,并探讨了均相晶体和立体复合晶体共存情况下的固相缩聚机理。结果表明,固相缩聚产物分子量增长的适宜反应条件为:反应时间30h,较低的催化剂含量,L-聚乳酸质量分数为80%。L-聚乳酸和D-聚乳酸共混物较低的初始立体复合晶体结晶度有利于后续固相缩聚过程中产物分子量的增长;固相缩聚不仅发生在异链之间,而且也发生在同链之间。     

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.     

聚丁二酸丁二醇酯与氯醚弹性体协同增韧改性聚乳酸多元共混体系

以来源于可再生资源聚丁二酸丁二醇酯(PBS)和氯醚橡胶(ECO)作为聚乳酸(PLA)的增韧改性剂,通过熔融共混的方法制备了PLA/PBS/ECO三元共混体系。动态力学分析和扫描电子显微镜结果表明,ECO促进了PBS和PLA之间的相容性。力学性能测试表明,ECO与PBS可实现对聚乳酸基体的协同增韧: PLA/PBS/ECO(70/20/10)显示出最优的拉伸性能,断裂伸长率高达270%;PLA/PBS/ECO(70/10/20)的冲击强度提高至23.7 kJ/m²,是纯聚乳酸的12倍。结合形态结构和冲击断面形貌分析表明ECO的存在可起到增容/增韧双重作用, 与柔性PBS产生良好的协同效应,有效改善聚乳酸材料的韧性。我们的研究表明,构造PLA-柔性生物聚酯和生物基弹性体多元共混体系是一种获得高性能生物基材料简单高效的手段。     

Photo-grafting Poly(acrylic acid) onto Poly(lactic acid) Chains in Solution

Poly(lactic acid)(PLA)is one of the most important bio-plastics,and chemical modification of the already-polymerized poly(lactic acid)chains may enable optimization of its material properties and expand its application areas.In this study,we demonstrated that poly(lactic acid)can be readily dissolved in acrylic acid at room temperature,and acrylic acid can be graft-polymerized onto poly(lactic acid)chains in solution with the help of photoinitiator benzophenone under 254 nm ultraviolet(UV)irradiation.Similar photo-grafting polymerization of acrylic acid(PAA)has only been studied before in the surface modification of polymer films.The graft ratio could be controlled by various reaction parameters,including irradiation time,benzophenone content,and monomer/polymer ratios.This photo-grafting reaction resulted in high graft ratio(graft ratio PAA/PLA up to 180%)without formation of homopolymers of acrylic acid.When the PAA/PLA graft ratio was higher than 100%,the resulting PLA-g-PAA polymer was found dispersible in water.The pros and cons of the photo-grafting reaction were also discussed.     

降解可控乳酸类聚合物

聚乳酸作为生物医用材料，其降解性能最为人们关注。根据降解性能的不同，其应用也有不同的用途。本文从共聚和共混两方面综述了聚乳酸在降解可控性方面研究的最新进展，对未来的工作进行了展望。     

Poly(lactic acid) Polymerized by Aluminum Triflate

The ring-opening polymerization of L -lactide (LA) has been initiated by aluminum triflate (trifluoromethanesulfonate) in air using a simple glass tube at 100 °C without desiccation steps and stirring. It was found that the molecular weight of poly(lactic acid) (PLA) was increased by the addition of an alcohol as an initiator to the reaction mixture. The highest number averaged molecular weight, molecular weight distribution, and recovery of the obtained PLA at 100 °C for 6 h were 18,200, 1.20, and 73%, respectively. With the addition of a small percentage of alcohol and a long reaction time of the polymerization method with the re-addition of LA, PLA (ca. 80 wt%) with a higher molecular weight (ca. 30,000) initiated by the added alcohol was produced with PLA (ca. 20 wt%) with a lower molecular weight (ca. 2,000) initiated by impurities such as water, which exist in a monomer, initiator, or catalyst.     

Poly(lactic acid)‐based nanocomposites

Classic plastics accumulate in nature causing environmental pollution, yet as a counterbalance they benefit society in many ways. They are versatile, cost‐effective, and can be tailored to have desired properties. The global environment has led to the fabrication of commodity plastics from environmentally degradable polymers. Poly(lactic acid) (PLA) is the most promising among the environmentally friendly polymers available. PLA‐based plastics have mechanical, thermal, and transparency similar to traditional plastics, and they can be molded and fabricated using the same equipment and procedures. Their material properties are enhanced through nanocomposites, compatibilizers, plasticizers, and other fillers (flame retardant, ultraviolet filter, etc.). This review summarizes mass production techniques and property reinforcements (focusing on nanocomposites and plasticizers) for PLA‐based plastics for commodity use. Copyright © 2016 John Wiley & Sons, Ltd.     

聚乳酸荧光防伪纤维的制备及其性能

通过熔融纺丝法成功制备了聚乳酸荧光防伪纤维。分别采用DSC、XRD、纤维强度仪、荧光光谱仪、荧光显微镜等探讨了荧光粉含量对聚乳酸荧光防伪纤维的结晶结构、力学性能与荧光性能的影响,并利用激光共聚焦显微镜对防伪纤维进行了3D荧光分布模拟分析。研究结果表明:聚乳酸荧光防伪纤维在紫外光激发下,在530nm处出现最强发射峰,纤维呈黄绿色荧光;随着荧光粉含量的增加,纤维的荧光强度增加,但荧光粉在基体中的团聚现象逐渐加剧,纤维的断裂强度逐渐降低;激光共聚焦显微镜可较好地模拟荧光防伪纤维中荧光粉的分布情况。     

溶剂诱导的聚乳酸/聚乳酸衍生物共结晶行为

通过溶液浇铸法制备不同组分的左旋聚乳酸(PLLA)和聚(L-2-羟基-3-甲基丁酸)(PL-2H3MB)共混物.运用差示扫描量热仪(DSC)、偏光显微镜(POM)、广角X射线衍射(WAXD)和热重分析仪(TGA)分析共混物的结晶、熔融行为和热稳定性.通过观察到DSC加热曲线中新的熔融峰判断PLLA和PL-2H3MB共晶...     

Fabrication of Poly(lactic acid) Diacrylate Nanospheres with Double Bonds

Summary: In this paper, unsaturated groups were introduced into poly(lactic acid) (PLA) for fabricating PLA‐based nanospheres with carbon‐carbon double bonds as functional groups. The morphology dependencies on fabrication conditions, including the fabrication time as well as the stirring rate, were also investigated.

SEM‐EDX image of poly(lactic acid) diacrylate nanospheres after exposure to osmium tetroxide vapor for 14 h.     

聚乳酸与聚乳酸-羟基乙酸多孔细胞支架的制备及孔隙的表征

应用溶液烧铸致孔剂浸出技术制备了不同致孔剂用量与不同致孔剂颗粒尺寸条件下的一系列聚乳酸及不同组成的聚乳酸－羟基乙酸多孔细胞支架;用一种改进的方法－重量法测定其孔隙率;在聚乳酸－羟基乙酸多孔支架上进行了软骨细胞培养。研究结果表明,随着制备过程中致孔剂用量的增加,多孔支架的孔隙逐渐增加,而与致孔剂的颗粒大小基本无关;致孔剂的颗粒大小只影响多孔支架的孔径;在致孔剂用量及致孔剂颗粒尺寸都相同的情况下,随着共聚物中乙交酯含量的增加,孔隙率逐渐下降;软骨细胞在支架上繁殖情况良好,三周后已开始分泌细胞外基质。     

聚乳酸共混体系的研究进展

聚乳酸是人工合成的可生物降解的热塑性脂肪族聚酯 ,是一种环境友好的材料 ,逐渐成为人们研究的热点。本文根据聚乳酸共混体系中另一组分的生物降解性 ,将聚乳酸共混体系分为完全可生物降解共混体系和部分可生物降解共混体系两类。针对体系的相容性和结晶结构以及在提高PLA的性能和降低成本等方面 .综述了聚乳酸共混体系的最新研究进展 ,并对其发展动态进行了简要介绍     

聚乳酸/蒙脱土纳米复合材料的结构和热性能

聚乳酸/蒙脱土纳米复合材料的结构和热性能;聚乳酸;蒙脱土;纳米复合材料;插层     

聚丁二酸丁二醇酯在堆肥条件下的生物降解性能研究

根据ISO 14855的检测方法,研究了聚丁二酸丁二醇酯(PBS)在堆肥条件下的生物降解性能,结果 表明PBS具有良好的生物降解性,且其形态对其降解速率有显著的影响,降解速率:PBS粉末>PBS片>PBS 颗粒。对堆肥中的微生物进行分离鉴定,在所选堆肥中主要分离出四种菌株:杂色曲霉菌、青霉菌、芽包杆菌 和直杆高温多孢菌,它们对PBS的降解能力各不相同,其中最有效降解PBS的菌株是杂色曲霉菌。     

聚对苯二甲酰十碳二胺的制备和非等温结晶动力学研究

以对苯二甲酸和癸二胺为原料,经成盐,预聚合和固相聚合三个步骤合成了新型长碳链和较高相对分子质量的半芳香尼龙聚对苯二甲酰十碳二胺,由红外光谱和核磁共振对其结构进行了确认。用DSC方法研究了聚对苯二甲酰十碳二胺的非等温结晶动力学,用莫志深提出的R～f法对非等温结晶动力学进行了分析,由R～t法得到α值在0.70～0．81之间。利用Kissinger方法求得了半芳香尼龙的非等温结晶活化能,△E=-297．08kJ／mol。     

Biodegradation of poly(lactic acid) and its nanocomposites

PLA nanocomposites based on organically modified montmorillonites at 5% w/w loading were prepared by melt blending using an internal mixer and then degraded in a commercial compost. The addition of nanoclays was found to increase the PLA degradation rate, especially for the highest dispersed clay in the polymer matrix. Biodegradation by microorganisms isolated from the compost showed the bacterium Bacillus licheniformis as one of the responsible for PLA biodegradation in compost. It was also found that clays can influence the polymer bacterial degradation depending on their chemical structure and affinity of the bacterium towards the clay.     

Effects of physical aging,crystallinity, and orientation on the enzymatic degradation of poly(lactic acid)

The effects of physical aging, degree of crystallinity, and orientation of poly(lactic acid) (PLA) were studied using differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). The samples of PLA with 96% [L] and 4% [D] contents were prepared by injection molding. The physical aging of PLA strongly depended on time and temperature. The change of rate of physical aging was very fast initially and slowed down as time increased. The enzymatic degradation of PLA was carried out with proteinase K at 37°C at a pH value of 8.6 in a Tris/HCl buffer solution. The enzymatic degradation rate was found to decrease as a function of physical aging (i.e., excess enthalpy relaxation). The rate of enzymatic degradation of PLA decreased with the increase in crystallinity. A threshold was observed when the heat of fusion was less than 20 J/g. The weight loss of PLA with a low level of crystallinity had no apparent change during any period of testing time. The rates of enzymatic degradation of stretched and injection-molded specimens were comparable. © 1996 John Wiley & Sons, Inc.