反应挤出合成聚乳酸技术研究

本文主要介绍了反应挤出合成聚乳酸的技术特点和脱挥技术应用,分析了反应挤出合成过程中脱挥处理的关键点和影响因素。     

双螺杆反应挤出法制备聚乳酸的研究

利用双螺杆挤出机将低摩尔质量的乳酸预聚物在挤出机上进一步缩聚,制备出较高摩尔质量的聚乳酸。研究了反应挤出温度、催化剂用量及螺杆转速等因素对该缩聚反应的影响。结果表明,当反应温度为150℃,催化剂用量为0．5％,螺杆转速为75r／min时,聚乳酸的摩尔质量能得到最大程度的提高。DSC分析表明,采用该法制得的聚乳酸的结晶度有所降低。     

聚乳酸／二异氰酸酯反应挤出扩链及其产物性能研究

以溶液法直接合成低相对分子质量聚乳酸为基础，在双螺杆挤出机上与二苯基甲烷二异氰酸酯进行反应挤出，制得高相对分子质量的聚乳酸基聚氨酯，研究了不同NOO／OH摩尔比对产物相对分子质量、热性能和力学性能的影响。结果表明，用反应挤出法对聚乳酸进行扩链是可行的，扩链后聚乳酸的黏均相对分子质量由9．19×10^4提高到23．6×10^4，韧性提高，拉伸断裂强度增大近1倍。     

热塑性聚氨酯弹性体反应挤出合成技术研究进展

介绍了反应挤出的概念和优点,综述了热塑性聚氨酯弹性体反应挤出合成技术的研究情况,展望了热塑性聚氨酯反应挤出合成技术的发展方向。     

双螺杆反应挤出制备马来酸酐接枝聚乳酸材料的研究

利用双螺杆挤出机制备马来酸酐接枝聚乳酸（MPLA）材料．研究了反应挤出工艺并测试了接枝产物的性能。结果表明：随着引发剂用量的增加或双螺杆转速的提高,产物黏度和熔体质量流动速率的变化总趋势是先降低后增高,而温度对挤出接枝反应的影响不明显;通过双螺杆挤出制备出的MPLA具有良好的亲水性和界面相容性。     

PVC的脱挥技术研究

文中介绍了PVC生产过程中氯乙烯单体含量的控制以及悬浮PVC中的VCM汽提,乳液PVC的脱挥等应用技术,提出了一定的解决方法。     

聚乳酸的合成研究

聚乳酸是一种由乳酸聚合而成的有机高分子材料,具有一定的机械强度和良好的成型加工性能,特别是其生物降解性,使聚乳酸在医药、外科手术及农药方面具有广泛的应用前景。从四十年代末至五十年代中,国外对聚乳酸的合成进行过研究,但作为结构材料它却没有什么可取之处,直到1966年Kulkarni首次报道聚乳酸能用于外科手术     

聚乳酸合成技术研究进展

聚乳酸因可生物降解、性能优异、应用广泛而深受青睐。本文介绍了2种主要化学合成聚乳酸的方法：丙交酯开环聚合法和乳酸直接缩聚法。分析了这2种方法的优势和缺陷：丙交酯开环聚合法设备简单,可得到大分子量的聚乳酸,缺点是成本较高,整个工艺复杂,路线长;乳酸直接缩聚法原料乳酸来源充足,价格便宜,单体转化率较高,工艺简单,不需要经过中间体的纯化,因而成本较低,缺陷是较难得到高分子量的聚合物。文中指出积极开展聚乳酸的合成工艺研发、进一步降低生产成本是当前聚乳酸研究的重要课题,重点在于简单易行的高分子量聚乳酸合成工艺的突破。     

双螺杆反应挤出

本文描述了反应挤出概念和特点,对不同类型的反应挤出用及双螺杆挤出机的特点进行了分析和比较,并介绍了双螺杆挤出机在反应挤出加工中的应用范围和实例。     

聚乳酸在挤出过程中的降解

以真空干燥后的聚乳酸(PLA)为实验原料,分别在料筒温度为170、190℃条件下进行挤出研究.主要研究挤出温度、螺杆转速对聚乳酸分子量的影响.结果表明:烘干后PLA分子力降低的主要原因是在挤出机内受剪切力后发生了力化学降解.随着螺杆转速的提高,剪切力增大分子量随之降低.挤出后的聚乳酸分子量在降低的同时,分子量分布也有所变小.     

Polymer Extrusion Devolatilization

Polymer devolatilization, including flash, surface renewal and stripping‐agent‐added techniques in screw extruders, is one of the most important polymer processing technologies. Its development requires an understanding of the relationships among some facts and subjects. Surface renewal devolatilization (SRDV) is a commonly used technique, which includes the two essential elements of film interface area and exposure time. A main feature of SRDV in various types of screw extruders is extrusion devolatilization, in which those elements vary with screw speed and throughput. An extrusion‐devolatilization model for SRDV model has been developed, which solves some important engineering problems encountered in devolatilization.     

Corotating Twin-Screw Extrusion Reactive Extrusion-Devolatilization Model and Software

The modular corotating twin-screw extruder is an increasingly widely used polymer processing machine. This paper describes analyses of reactive extrusion and devolatilization in a modular corotating twin-screw extruder. The results of the analyses are intergrated into a comprehensive model and computer software for the modular corotating twin-screw extrusion process.     

Poly (lactic acid) foaming

Poly (lactic acid) or polylactide (PLA) is an aliphatic thermoplastic polyester produced from renewable resources and is compostable in the environment. Because of the massive use of foamed products of petroleum-based polymers, PLA foams have been considered as substitutes for some of these products. Specifically, because of PLA's competitive material and processing costs, and its comparable mechanical properties, PLA foams could potentially replace polystyrene (PS) foam products in a wide array of applications such as packaging, cushioning, construction, thermal and sound insulation, and plastic utensils. Due to their biocompatibility, PLA foams can also be used in such biomedical applications as scaffolding and tissue engineering. But PLA has several inherent drawbacks, which inhibit the production of low-density foams with uniform cell morphology. These drawbacks are mainly the PLA's low melt strength and its slow crystallization kinetics. During the last two decades, researchers have investigated the fundamentals of PLA/gas mixtures, PLA foaming mechanisms, and the effects of material modification on PLA's foaming behavior through various manufacturing technologies. This article reviews these investigations and compares the developments made thus far in PLA foaming.     

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。     

活性聚乳酸的制备与性能

利用季戊四醇、丙烯酸与乳酸合成支化结构的端双键聚乳酸,再经热固化制备交联聚乳酸。通过红外光谱仪、凝胶渗透色谱仪和差示扫描量热仪对材料的结构和性能进行研究。结果表明,季戊四醇用量越少的聚合物分子量越大,但其凝胶含量则持续下降,且季戊四醇的加入降低了聚合物的玻璃化转变温度和熔融温度。     

反应挤出法制备LLDPE-g-(GMA-co-St)的研究

以甲基丙烯酸缩水甘油酯(GMA)为接枝单体,苯乙烯(St)为接枝共单体,在双螺杆挤出机上对线型低密度聚乙烯(LLDPE)进行熔融接枝,制备了LLDPE-g-(GMA-co-St).研究了引发剂用量、单体用量、共单体用量和抑交联剂亚磷酸三苯酯等对LLDPE接枝物接枝率和熔体质量流动速率的影响,利用红外光谱对接枝物进行了表征.研究表明,St的加入能有效提高GMA的接枝率,亚磷酸三苯酯有效抑制了LLDPE的交联.最佳配方为:过氧化二异丙苯(DCP)为0.15份,GMA为3份,St为3份,亚磷酸三苯酯为1份.     

Poly(lactic acid) mass transfer properties

Poly(lactic acid) (PLA), a biodegradable and compostable polymer, is gaining market acceptance and has been extensively investigated. The versatility of PLA has led to its broad and different applications in medical, agriculture, and food packaging fields. Similar to other polymers, PLA is permeable to gases, vapors and organic compounds. Thus, the mass transfer properties of PLA can influence its suitability for end-use applications. Here, we present a comprehensive, systematic, and critical review of more than 300 papers published since 1990 reporting the mass transfer properties of PLA, which include permeability, diffusion and solubility to gases, water vapor and organic vapors, along with migration of chemical compounds from PLA. Overall, PLA provides moderate barrier to gases, water vapor, and organic compounds. Barrier enhancement can be achieved through modifications such as blending with other polymers and formation of composite structures. Most of the mass transfer parameters reported in the literature are based on two-phase mobile amorphous and crystalline fractions, omitting the role of the restricted amorphous fraction, which can lead to unclear comprehension of PLA barrier properties as well as what affects those properties. Additional research is needed to address this shortcoming. This review provides an in-depth analysis of PLA mass transfer and a foundation for future research and commercial development.     

可生物降解聚乳酸纳米粒的制备及表征

采用乳化 -溶剂蒸发法 ( O/W)制备聚乳酸 ( PLA)纳米粒 ,用透射电子显微镜和激光粒度仪对纳米粒进行了表征 ,纳米粒具有规整的球形且正态分布 ,同时从有机相和水相的体积比、聚合物的浓度、表面活性剂的选择及表面活性剂的浓度等几个因素对纳米粒粒径大小的影响作了较详细地讨论。有机相与水相的体积比从 1∶ 3减小到 1∶ 30 ,纳米粒的粒径从 ( 30 6.2 + 1 1 ) nm减小到( 1 87.1 + 2 .4) nm;聚合物在有机相的浓度从 1 %(质量分数 )增加到 5 %(质量分数 ) ,纳米粒的粒径从 1 94nm增加到 32 1 nm;随着水相中表面活性剂浓度从 0 .5 (质量体积分数 )增大到 3.5 %(质量体积分数 ) ,纳米粒粒径从 2 0 2 nm减小 1 78nm且有一个低的多分散指数。而且还比较了搅拌蒸发法和减压抽提法对纳米粒表面形态的影响     

Poly(lactic acid) Toughening with a Better Balance of Properties

Poly(lactic acid) (PLA) toughening is often associated with significant modulus and/or strength losses making it unsuitable for many consumer and biomedical applications. The major objective of this research was to toughen PLA without significant loss in modulus and strength and to introduce reactive acid groups using reactive blending of PLA with a combination of polymers. PLA was reactive blended with poly(acrylic acid) (PAA) followed by physical blending with poly(ethylene glycol) (PEG) in solution. The modified PLA was extruded into films using a co‐rotating twin‐screw extruder and characterized using tensile testing, differential scanning calorimetry (DSC), and dynamic mechanical analyses (DMA). This technology resulted in films with a ten‐fold increase in toughness compared to neat PLA with little or no decrease in strength and modulus.