聚乳酸成核剂的研究进展

回顾并展望了聚乳酸成核剂的研究与开发进展,比较和评价了不同类型成核剂对聚乳酸结晶行为的影响,在此基础上提出了开发聚乳酸专用成核剂的思考和建议。     

可降解聚乳酸的合成及改性研究进展

介绍了可降解材料聚乳酸树脂的合成与改性方法。合成聚乳酸的主要方法有开环聚合、直接缩聚合等。通过共聚、共混、嵌段、接枝、纤维复合可以对聚乳酸进行改性,改进聚乳酸的结构与性能,以进一步扩大应用范围。     

熔融缩聚法制备聚乳酸

通过熔融缩聚法制备了聚乳酸。探讨了反应温度、催化剂类型及用量、反应时间对聚乳酸的影响，并用红外光谱和1↑H NMR对聚合物进行了表征。结果表明，最佳的反应条件为：聚合时间30h左右、聚合温度160℃、以O．2％的对甲苯磺酸作为酸催化剂、O．5％的氯化亚锡为催化剂、真空度为O—1333Pa；而提高乳酸纯度是制备高摩尔质量聚乳酸的关键条件之一。     

聚乳酸-天冬氨酸生物降解材料的合成

含亲水性羧基的聚乳酸-天冬氨酸（PAL）的合成方法有直接法和间接法,但是其产物降解周期难以控制,韧性和抗冲击能力较差。文章通过共聚得到了较好力学性能的生物降解材料。含亲水性羧基的聚乳酸-天冬氨酸（PAL）的结构通过理化常数及光谱分析得到确证。文章所述的合成方法是一条简便,可行的且具备重复强的合成工艺路线。     

聚乳酸及其共聚物的体外降解方法

聚乳酸(PEA)是一类高分子聚酯,凡是能引起酯键断裂的因素都可以使聚乳酸发生降解。本文综述了聚乳酸(PEA)及其共聚物的化学降解、酶降解、超声波降解、辐射降解和微生物降解的体外降解方法及降解机理。     

增塑剂对生物降解塑料聚乳酸结晶形态的影响

采用熔融共混方法制备了聚乙二醇(PEG)和聚乳(酸PLA)的共混物,并借助差示扫描量热仪和广角X射线衍射仪研究了在80~140℃等温结晶时PEG对PLA结晶形态和熔融行为的影响。结果表明:100℃以上时PLA的结晶度随结晶温度的升高逐渐增加;100℃以下时PLA的结晶度随PEG含量的增加逐渐增大。110℃以下时,晶面间距随结晶温度的升高和PEG含量的增加而逐渐减小;110℃以上时,晶面间距保持不变;当加入15%的PEG时PLA的晶面间距不受结晶温度的影响结,晶生成的是稳定的α晶。     

Study on the Crystallization Kinetic and Characterization of Poly(lactic acid) and Poly(vinyl alcohol) Blends

In this study, poly(lactic acid) (PLA) and poly(vinyl alcohol) (PVA) blends, with PLA/PVA mass ratios of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50, and 40/60, were prepared by means of the melt blending method. The result of torque measurements and thermal gravimtric analysis tests showed that the addition of PLA can decrease the melt viscosity of PVA and that the second degradation step of PVA nearly disappeared for the PLA₈₀/PVA₂₀ blend. The absorbance peaks of the carbonyl group and the hydroxyl group in the Fourier transform infrared spectra of PLA/PVA blends had significant shifts to lower wave numbers, indicating that there were interactions between these two groups. Combined with the result of the differential scanning calorimetry curves, this interaction would be favorable for improving miscibility. The X-ray diffraction patterns and the polarized light microscope (PLM) micrographs showed that PVA can serve as a nucleating agent to promote the crystallization of PLA in PLA/PVA blends. Moreover, the PLA₈₀/PVA₂₀ blend gave the highest growth rate of PLA spherulite.     

Reactively Modified Poly(lactic acid): Properties and Foam Processing

Summary: In order to produce modified poly(lactic acid) (PLA) resins for applications requiring high melt viscosity and elasticity (e.g., low‐density foaming, thermoforming), a commercial PLA product has been reactively modified in melt by sequentially adding 1,4‐butanediol and 1,4‐butane diisocyanate as low‐molecular‐weight chain extenders. By varying amounts of the two chain extenders associated to the end group contents of PLA, three resulted samples were obtained. They were then structurally characterized by FTIR spectroscopy and molecular structure analysis. Their thermal, dynamic mechanical thermal properties and melt viscoelastic properties were investigated and compared along with unmodified PLA. The results indicated that chemical modification may be characterized as chain scission, extension, crosslinking, or any combination of the three depending on the chain extender amounts. The increase of PLA molecular weight could be obtained by properly controlling amounts of two chain extenders. The samples with increased molecular weights showed enhanced melt viscosity and elasticity. Such property improvements promised a successful application for modified PLA in a batch foam processing by producing foams with reduced cell size, increased cell density and lowered bulk foam density in comparison with plain PLA foam.

Cellular morphology of a modified PLA foam.     

生物医用高分子材料聚乳酸的成型方法研究

对聚乳酸的一些成型方法作了概述。包括聚乳酸纤维的纺丝成型、自增强成型、泡沫材料的成型。聚乳酸材料的成型可采用注射、挤出、压制等方法，但其制品的力学性能难以满足某些医疗修复器件的要求。经熔融纺丝、自增强成型等特殊成型方法可以获得力学性能较高的制品，聚乳酸泡沫材料可用于组织工程。     

聚乳酸基抗菌材料的研究进展

分别介绍了聚乳酸基无机抗菌材料、有机抗菌材料及天然抗菌材料的研究现状,提出了目前存在的问题,并对聚乳酸基抗菌材料未来的发展趋势进行了展望。     

Poly(lactic acid)/carbon nanotube nanocomposites with integrated degradation sensing

For the first time, an in-situ degradation monitoring system for biodegradable polymers is reported in present work. The proposed concept is based on a conductive biodegradable polymer composite, where carbon nanotubes (CNTs) are incorporated in poly(lactic acid) (PLA) in order to develop an intelligent biocomposite system that can sense biodegradation. Changes in electrical resistivity of the PLA/CNT nanocomposites were successfully correlated with degradation levels of the biopolymer. PLA/CNT nanocomposites demonstrated excellent degradation sensing abilities at CNT concentrations around the percolation threshold, with resistivity changes of about four orders of magnitude with biodegradation. In contrast to many other stimuli, biodegradation resulted in a reduction in resistivity due to an increased CNT network density after partial removal of the amorphous phase of the polymer matrix.     

增塑剂对聚乳酸性能的影响

对不同增塑聚乳酸体系的力学性能、脆韧转变现象和增塑剂的迁移性能进行了研究。实验表明：增塑剂品种不同对聚乳酸的增塑效果不同,三种增塑剂中柠檬酸三丁酯(TBC)的增塑效果最佳；TBC的质量分数小于10%时,增塑体系的脆性基本不变,TBC的质量分数在10%～13%时,材料出现脆韧转变；增塑聚乳酸体系增塑剂迁移率随增塑体系相容性的增加而减小,随增塑剂用量增加而增大。     

聚乳酸有机成核剂研究进展

聚乳酸作为生物可降解材料应用广泛,但是结晶速率非常慢,添加成核剂可以改善其结晶速率,其中有机成核剂因其与聚乳酸良好的相容性备受关注。本文重点综述了有机成核剂的种类及其对聚乳酸结晶性能的改善情况,并展望了有机成核剂今后的发展方向。     

Water Absorption of Poly(lactic acid) Nanocomposites: Effects of Nanofillers and Maleated Rubbers

Injection-molded poly(lactic acid)/organo-montmorillonite (PLA/OMMT) and poly(lactic acid)/ nano-precipitated calcium carbonate (PLA/NPCC) were exposed to a water absorption test at 30°C for 70 days. The analysis was focused on the water diffusion kinetics and impact strength changes induced by the hydrolysis. The diffusion exponent (n) values of all the PLA samples are less than 0.5, indicating the Fickian diffusion model (case I) is obeyed. Adding nanofillers and maleated rubbers (SEBS-g-MAH or EPR-g-MAH) increased equilibrium moisture content but decreased diffusion coefficient values of PLA. The recoverability and retention-ability of the maleated rubbers toughened PLA/OMMT and PLA/NPCC after water absorption are excellent.     

聚乳酸结晶的研究进展

综述了自合成以来聚乳酸（PLA）结晶行为研究的主要成果，介绍了PLA的α、β、γ三种晶型结构参数及不同晶型晶体的形成条件，以及PLA球晶、单晶、孪晶、微纤晶和串晶等结晶形态及其形成条件。此外，还介绍了PLA在不同条件下的结晶行为，着重阐述了分子结构、第二组分及温度场、应力场以及辐照等外部因素对其结晶行为的影响。     

Synthesis and thermal properties of telechelic poly(lactic acid) ionomers

Telechelic poly(lactic acid) (PLA) ionomers were synthesized using a chemical recycling process. A transesterification reaction between a commercial PLA and 2-hydroxyethyl methacrylate or ethylene glycol was used to produce a hydroxy-terminated PLA. The hydroxy-terminated PLA was then reacted with itaconic anhydride to produce terminal carboxylic acid groups, which were neutralized with appropriate metal acetates to produce Na-, Li-, K-, Zn-, Ca- and Y-ω- and α,ω-telechelic PLA ionomers. ¹H NMR spectroscopy was used to confirm the presence of the itaconic acid end-groups and FTIR spectroscopy was used to quantify the extent of neutralization. The addition of the ionic groups increased the glass transition (T_g), and T_g increased as the strength of the ion-pair increased. The ionic groups suppressed crystallinity, especially when multivalent cations were used.     

Synthesis and properties of random poly(lactic acid)-based ionomers

A random poly(lactic acid), PLA, based ionomer was synthesized by copolymerizing a methacrylate-terminated PLA macromonomer and methyl methacrylate. The copolymerization kinetics were studied using ¹H NMR spectroscopy and the copolymer composition was characterized by ¹³C NMR spectroscopy. Carboxylic acid groups were introduced into the copolymer by reacting the hydroxyl end groups of the PLA macromonomer with succinic anhydride, and the acid groups were neutralized with metal acetates to produce Na-, Ca-, and Y-PLA ionomers. Significant increases in T_g were observed for the ionomers and thermomechanical analysis indicated that the ionomers were more resistant to penetration by a weighted probe and an apparent rubbery plateau was observed above T_g. The ionomers were more hydrophilic than PLA, but relatively low water absorption could be achieved for the Ca²⁺-salt ionomer.     

Poly(l-lactide)/nano-structured carbon composites: Conductivity, thermal properties, crystallization, and biodegradation

The effects of nano-structured carbon fillers [fullerene C₆₀, single wall carbon nanotube (SWCNT), carbon nanohorn (CNH), carbon nanoballoon (CNB), and ketjenblack (KB)] and conventional carbon fillers [conductive grade and graphitized carbon black (CB)] on conductivity (resistance), thermal properties, crystallization, and proteinase K-catalyzed enzymatic degradation of poly(l-lactide) [i.e., poly(l-lactic acid) (PLLA)] films were investigated. Even at low filler concentrations such as 1 wt%, the addition of SWCNT effectively decreased the resistivity of PLLA film compared with that of conventional CB, and PLLA-SWCNT film with filler concentration of 10 wt% attained the resistivity lower than 100 Ω cm. The crystallization of PLLA further decreased the resistivity of films. The addition of carbon fillers, except for C₆₀ and CNB at 5 wt%, lowered the glass transition temperature, whereas the addition of carbon fillers, excluding C₆₀, elevated softening temperatures, if an appropriate filler concentration was selected. On heating from room temperature, cold crystallization temperature was determined mainly by the molecular weight of PLLA, whereas on cooling from the melt, the carbon fillers, excluding KB, elevated the cold crystallization temperature, reflecting the effectiveness of most of the carbon fillers as nucleating agents. Despite the nucleating effects, the addition of carbon fillers decreased the enthalpy of cold crystallization of PLLA on both heating and cooling. The addition of CNH, CNB, and CB elevated the starting temperature of thermal degradation of PLLA, whereas the addition of SWCNT reduced the thermal stability. Furthermore, the addition of C₆₀ and SWCNT enhanced the enzymatic degradation of PLLA, whereas the addition of KB and CNB disturbed the enzymatic degradation of PLLA. The reasons for the effects of carbon fillers on the physical properties, crystallization, and enzymatic degradation of PLLA films are discussed.     

聚乳酸耐热改性的研究

研究了一种耐热聚乳酸,并对其进行了红外光谱、示差扫描量热分析、热重分析、X-射线衍射、热收缩及断裂强力等测试。同样条件下,这种耐热聚乳酸的热收缩率是普通聚乳酸的1/4,耐热性有了明显改善,强力略有提高。