反应挤出合成聚乳酸与脱挥技术研究

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。相比传统的聚乳酸合成技术,因其具有突出的优势,预计是今后聚乳酸合成发展的研究热点。     

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。     

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。     

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。     

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.     

反应挤出研究的趋向

从反应挤出的反应例子、技术特征及可能性、装置要求、工艺分析方面介绍关于反应挤出的基础研究的趋向,同时从新的侧面将反应挤出技术体系化。     

Reactive extrusion of zein with glyoxal

Cross‐linked zein has been produced using glyoxal (GLY) as the cross‐linking reagent via reactive extrusion for the first time in a twin screw extruder using dilute sodium hydroxide as catalyst. Tri(ethylene glycol) was used as a plasticizer for various items. The extrudate was then ground and processed using either compression or injection molding. At the highest level of GLY (6%), tri(ethylene glycol) was used at 10% as a plasticizer to allow further processing to take place. With this formulation, samples could be obtained from the injection mold, however, the samples did not hold their molded shape due to the elasticity of the sample at the mold temperature. When lower levels of GLY were used, injection molded sample bars of similar quality to control were obtained. The physical properties of these samples were similar to control. At GLY levels of 1.75% and higher, the samples were resistant to dissolution by acetic acid. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Reactive extrusion of polyolefin ternary blends

Reactive extrusion of polypropylene (PP)/ethylene–propylene–diene terpolymer (EPDM)/high-density polyethylene (PE) (80/10/10 by weight) blends were carried out using a corotating twin-screw extruder. The effects of peroxide and coagent concentrations and extruder rpm were studied in terms of rheological, morphological, thermal, and mechanical properties of the blends. Melt viscosity of the peroxide-treated blend increased and decreased over the untreated one depending on the amount of a coagent. Morphologically, interfaces blur with only a peroxide treatment, and significant domain reduction was obtained when peroxide and a coagent were used together. Both T_m (crystalline melting temperature) and T_g (glass transition temperature) of PP increased in the blend, whereas those of PE slightly decreased. © 1996 John Wiley & Sons, Inc.     

Maleation of polylactide (PLA) by reactive extrusion

Free‐radical‐initiated grafting of maleic anhydride (MA) onto a polylactide (PLA) backbone was performed by reactive extrusion. A concentration of 2 wt % MA in the presence of 2,5‐dimethyl‐2,5‐di‐(tert‐butylperoxy)hexane (Lupersol 101) as the free‐radical initiator was used for all experiments. Two reaction temperatures were studied (180 and 200°C) with a peroxide initiator concentration between 0.0 and 0.5 wt %. Under these conditions, between 0.066 and 0.672 wt % MA was grafted onto the PLA chains. Triple‐detector size‐exclusion chromatography (TriSEC), melt flow index (MFI), and thermal gravimetric analysis (TGA) were used to characterize the maleated PLA polymers. Increasing the initiator concentration resulted in an increase in the grafting of MA, as well as a decrease in the molecular weight of the polymer. The maleation of PLA proved to be very efficient in promoting strong interfacial adhesion with corn native starch in composites as obtained by melt blending. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 477–485, 1999     

Reactive extrusion of recycled bottle waste material

The objective of this study is to investigate the effect of reactive processing of commingled bottle waste polymer in an extruder. A variety of peroxides and monomers were tested to assess their influence on the final mechanical properties of the product. The reactive extruded polymer blends were prepared in two types of extruders: a co‐rotating twin‐screw extruder and a Buss co‐Kneader single‐screw extruder. Blends were analyzed for mechanical and thermal properties. The effectiveness of the different monomers and peroxides was evaluated in terms of improvement in impact properties. It has been found that the toughness of the polymer blend is improved by reactive processing. Depending on the amount and type of reactants, the impact strength can be improved by 220%, with a slight reduction in the modulus compared to an unmodified physical blend. The most suitable monomers were n‐butylmethacrylate (BMA), t‐butylamino ethylmethacrylate (TBAEMA) and a combination of styrene/maleic anhydride (ST/MAH). The peroxide should have a short half‐lifetime compared to the average residence time in the extruder. The most effective monomers have a high initial reactivity and low rate of evaporation at the processing conditions used. Changes in processing conditions in the extruder influence the reaction conditions and therefore the final properties of the blend. Results were interpreted in terms of residence time, melting profile and peroxide concentration.     

热塑性弹性体的反应挤出动态硫化

介绍了制备热塑性动态硫化胶的反应挤出动态硫化技术的发展历史,系统论述了该技术的特点、工艺条件、硫化速率及硫化过程。     

Reactive extrusion of polystyrene/polyethylene blends

The feasibility of inducing beneficial changes to polystyrene/polyethylene (PS/PE) blends via reactive extrusion processes is considered. Experiments have been conducted on 50:50 wt.% PS/PE blends that were treated with different levels of dicumyl peroxide and triallyl isocyanurate coupling agent. Both a low molecular weight and a high molecular weight blend series have been investigated. A “more reactive” polystyrene was synthesized by incorporation of a minor amount of ortho-vinylbenzaldehyde. Blends containing this modified polystyrene were subjected to identical processing' conditions on a counter-rotating twin screw extruder. Examination of the tensile properties of the extrusion products suggested that a judicious level of peroxide and coupling agent additives would be beneficial to the ultimate physical properties. The quantity of styrenic phase becoming chemically grafted to the polyethylene matrix was influenced most strongly by the level of the chosen coupling agent. As determined by scanning electron microscopy, the phase morphologies of the tensile test fracture surfaces were strongly dependent upon the reaction extrusion process; those extruded blends that had been exposed to the additive pre-treatment displayed substantially finer microstructure. The enthalpy of fusion of the polyethylene melting endotherm was likewise influenced by both the presence or absence of the additives as well as the molecular weight nature of the blend series.     

微细发泡挤出成型的现状和展望

近年来．地球越来越变暖．为了防止地球温室效应．我们必须减少化石能源的使用量．很多公司也致力于研制开发减少能源消费量的新制品。对于塑料制品性能的要求也不断地提高．如制品     

Reactive extrusion of PP/natural rubber blends

Reactive extrusion of polypropylene (PP)/natural rubber (NR) (90/10) blends was conducted in the presence of a peroxide [1,3-bis(t-butylperoxy)benzene] and coagent (trimethylolpropanetriacrylate, TMPTA). Effects of peroxide and coagent content were studied in terms of melt index (MI), melt viscosity, morphology, thermal, and mechanical properties. At a constant content of the coagent, melt viscosity increased at a low and decreased at a high content of the peroxide. On the other hand, melt viscosity increased monotonically with the coagent concentration at constant peroxide content. The increase and decrease of viscosity were interpreted in terms of crosslinking and chain scission of PP, which governed the rubber domain size and mechanical properties of the reactive blends. © 1995 John Wiley & Sons, Inc.     

Reactive extrusion of polypropylene I: Controlled degradation

Polypropylene was degraded by injection of a free-radical initiator during extrusion. Molecular weight distribution, molecular weight averages, and melt flow index were measured to see the effect of initiator concentration (0.00 to 0.04 wt%), temperature (200 and 220°C), and screw rpm (31 and 44). Initiator concentration was the most significant variable. In all cases, increased initiator concentration degraded the high molecular weight tail of the polypropylene and narrowed the molecular weight distribution. Melt flow index varied linearly with initiator concentration beyond 0.01 wt% initiator. Reaction temperature had no effect on the measured properties of the extrudate. This was attributed to the minimum residence time in the extruder being sufficient for all degradation reactions to be completed. It also implied that the same reactions occurred at both temperatures. Increased screw rpm slightly increased molecular weight. No interaction among initiator concentration, temperature, and screw rpm was observed.