聚乙烯醇的熔融加工工艺与性能研究

本文主要研究了聚乙烯醇的熔融加工工艺及其性能。聚乙烯醇是一种生物可降解高分子材料,但是聚乙烯醇分子链中含有大量的羟基,容易在分子内或分子间形成大量的氢键,熔融温度高于分解温度,熔融加工困难。本实验通过甘油和芥酸酰胺复配作为增塑剂,降低聚乙烯醇的熔点,使其能够在适合的加工工艺下熔融加工。并以轻质碳酸钙为填料,对聚乙烯醇进行填充改性。实验表明,在增塑剂为20份,轻质碳酸钙为30份时,拉伸强度得到明显提高。     

可熔融加工聚乙烯醇的研究现状

熔融加工是一种相对简单、高效的加工方法。由于聚乙烯醇(PVA)的热分解温度很接近其熔点,使其难以熔融加工。为实现PVA的熔融加工,可以用溶剂增塑、共聚和共混等增塑(改性)技术来达到。近年来,对可熔融加工聚乙烯醇的需求也日益迫切。综述了近年来该领域的研究进展情况。     

长链乙烯酯改性聚乙烯醇热塑加工性能的研究

通过山梨醇和甘油复配增塑改善长链乙烯酯改性聚乙烯醇(PVA)的热塑加工性能,采用差示扫描量热仪、高压毛细管流变仪、万能试验机等研究了复配增塑剂与改性PVA的相互作用及其对改性PVA热性能、流变性能、力学性能、溶胀性能等的影响。结果表明,山梨醇和甘油复配增塑剂中的羟基可与改性PVA分子链中的羟基形成氢键,减小了PVA分子链间氢键相互作用,使体系黏度减小,分子链的活动性增强,降低了改性PVA熔点,改善了PVA熔体流动性,有利于实现PVA的热塑加工。复配增塑剂增加了PVA的自由体积,使PVA分子链的运动更加容易,提高了材料的柔韧性及断裂伸长率,减少PVA对水的吸收。当增塑剂含量为10%时,复配增塑剂不易析出,可同时改善改性PVA的流变性并使材料保持优异的力学性能。     

高熔点多元醇增塑聚乙烯醇的制备与性能

以高熔点多元醇季戊四醇(TMM)为主增塑剂、辅以相容剂和润滑剂形成复配增塑剂,对聚乙烯醇(PVA)进行增塑改性,以增大温度加工窗口,提高其热稳定性,实现改性PVA的熔融加工成型。采用差示扫描量热仪(DSC)、热重分析仪(TGA)、熔体指数仪测试了改性PVA的热性能和流动性能;采用扫描X射线衍射(XRD)、电子显微镜(SEM)对其结晶结构与形貌进行了测试与观察;然后进行了力学性能测试。结果表明,高熔点多元醇增塑剂用于增塑PVA,具备降低PVA的熔点,提高分解温度,增加流动性,使改性PVA具有良好的熔融加工性能,可用于注塑与挤出加工,制品具备良好的力学性能。     

淀粉基可降解塑料研究进展

热塑性淀粉具备优异的降解性能,其原料廉价易得、产品价格有竞争力,可缓解传统塑料对石油基的依赖。然而淀粉分子具有大量可以形成分子间或分子内氢键的羟基结构,使淀粉的熔融温度高于分解温度从而不具塑性,且淀粉的热稳定性以及流动性差不能满足塑料生产需求,需要对其进行改性方可使用。从淀粉的结构、物理改性、化学改性、共混改性四个方面进行综述。     

改性聚乙烯醇的热性能

采用DSC、TGA等测试，研究了6种PVA改性体系中改性剂对PVA热性能的影响。初步表征了各体系的成膜性能。实验结果表明，改性剂与PVA分子间发生强烈的相互作用，从而降低了PVA的熔点，提高了其热分解温度，在不同程度上改善了PVA的熔融性，通过热压成型可以将改性PVA制成透明性很好的薄膜。     

聚乙烯醇改性研究进展

聚乙烯醇(PVA)是一种水溶性的高分子,分子链上含有大量羟基,分子主链为反式-左右式平面锯齿形结构,主链上并没有支链,易结晶,其结晶结构为斜方晶系,结晶度很高,可以达到65%至75%,且PVA分子链直径小,分子间作用力强,极性大。文中详解了各种改性机理,并对现有PVA改性的基本类型方式进行了阐述。     

聚乙烯醇吹膜加工性能研究

研究了聚乙烯醇(PVA)吹膜加工性能。经两种不同的增塑剂复配增塑后，可明显改善其加工流动性，当复合增塑剂用量为25phr以上，PVA可以被较好地增塑，熔融塑化温度趋于定值。热性能研究表明，PVA为不完全结晶，其熔融曲线呈不规则分布。从PVA的流变性能可知，PVA熔体呈非牛顿性流体，剪切粘度随剪切速率增加而下降，并且醇解度较高的树脂，剪切粘度也较高。不同醇解度的PVA树脂，均能通过增塑改性后熔融挤出加工吹塑成膜。高醇解度PVA膜的水溶解温度高，而低醇解度PVA膜具有低温快速水解的性能。     

粹文详摘

CW189 聚乙烯醇的吹膜工艺聚乙烯醇(PVA)具有水溶性和生物降解性,用作包装薄膜较一般的包装材料在透明度、光泽、抗静电、透湿、耐油耐有机溶剂、热熔性、强韧性及印刷性能等方面都优于聚烯烃膜。PVA膜的生产方法有水溶液涂布法和熔融吹塑法,作为包装膜最常用的是熔融吹塑法。但是由于PVA分子内存在很多氢链结晶度又高,使它的熔融温度高于分解温度而难以热塑成型。故在PVA的热加工时须选用合适的增塑剂和润滑剂以降低它的熔体粘度和熔融温度,提高加工温度下的热稳定性。本文主要研究了不同醇解度和聚合度的PVA的成膜加工条件、流变性…     

聚乙烯醇的共混改性

将两种牌号聚乙烯醇(PVA)(PVA1799和PVA0599)混合,然后分别加入甘油/三甘醇、甘油/乙酰胺复合增塑剂对其进行改性。加入复合增塑剂使PVA1799/PVA0599的熔点、结晶度和热分解温度降低;与PVA1799/PVA0599体系相比,改性PVA1799/PVA0599的拉伸强度下降、拉伸断裂应变明显提高;随着PVA0599含量增加,改性PVA1799/PVA0599的熔体流动速率增大;m(PVA1799)/m(PVA0599)为3∶2时,随复合增塑剂用量增加,改性PVA1799/PVA0599的流动性变好;甘油/乙酰胺增塑效果优于甘油/三甘醇;改性PVA1799/PVA0599体系在复合增塑剂为30 phr时可望实现熔融加工。     

Melt‐processable and self‐healing poly(vinyl alcohol) elastomer containing diol groups in the side chain

A 3‐amino‐1,2‐propane diol functionalized poly(vinyl alcohol) elastomer (PVA–COO–AP) with melt processability and self‐healing properties was prepared by chemical graft modification, that is, a poly(vinyl alcohol) (PVA) carboxylation and carbodiimide reaction. Unlike that of conventional PVA modifiers, the incorporation of diol groups in the 3‐amino‐1,2‐propane diol molecules onto PVA chains reduced the breaking of intrinsic hydrogen‐bonding interactions of PVA because of the formation of new hydrogen bonds between the diol groups and the hydroxyl groups of PVA. PVA–COO–AP possessed a lower melting temperature and a higher decomposition temperature than PVA; this enabled the melt processing of PVA. The PVA–COO–AP samples prepared by compression molding exhibited excellent flexibility and elasticity, and the samples with a lower glass‐transition temperature below ambient temperature could be self‐healed because of the existence of dynamic hydrogen bonds. AP–COO–AP is believed to have potential applications in the fields of fibers and biomedical membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46050.     

Water states and thermal processability of boric acid modified poly(vinyl alcohol)

To further improve the processability of water plasticized poly(vinyl alcohol) (PVA), boric acid (BA), which can rapidly form reversible crosslinked structure with the hydroxyl groups of PVA, was adopted as a modifier, and the water states, thermal performance, and rheological properties of modified PVA were investigated. The results showed that ascribing to the formation of the crosslinked structure between PVA and BA, the content of nonfreezing water in system increased, indicating that the bondage of PVA matrix on water enhanced, thus retarding the tempestuous evaporation of water in system during melt process and making more water remained in system to play the role of plasticizer. Meanwhile, this crosslinked structure shielded part hydroxyl groups in PVA chains, leading to the further weakening of the self‐hydrogen bonding of PVA, and guaranteeing a lower melting point and higher decomposition temperature, thus obtaining a quite wide thermal processing window, i.e., ≥179°C. The melt viscosity of BA modified PVA slightly increased, but still satisfied the requirements for thermal processing, thus reinforcing the flow stability of the melt at high shearing rate. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43246.     

Dopamine‐functionalized poly(vinyl alcohol) elastomer with melt processability and self‐healing properties

A dopamine‐functionalized poly(vinyl alcohol) (PVA) elastomer with melt processability and self‐healing properties was prepared by a new chemical route of graft modification, that is, PVA carboxylation and a carbodiimide reaction. The conventional modifier for PVA sacrificed the intrinsic hydrogen‐bonding interactions and dramatically decreased the mechanical strength. The modifier dopamine, as a catechol derivative, has two hydroxyl groups, which formed hydrogen bonds with the hydroxyl groups of PVA; it also has one benzene ring, which increased the thermal stability. We found that the introduction of dopamine into the PVA molecular structure lowered the melting point, improved the thermal stability, broke the crystalline structure, and enabled thermal processing. Moreover, the modified PVA possessed good mechanical properties, could be self‐healed, and is believed to have potential applications in many fields. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45072.     

聚乙烯醇的热氧老化与稳定性研究

研究了聚乙烯醇（PVA）热氧环境下老化所发生的化学反应,以及磷酸酯类和酚类复合稳定剂对PVA热稳定性能的影响。傅里叶红外光谱、x射线光电子能谱分析结果表明：受热后PVA分子链上的羟基在高温下发生了消除反应,分子链上生成了C＝C共轭双键。HAAKE塑化仪、黄度指数及力学性能研究表明：复合稳定剂的加入可以有效抑制PVA在加工过程中产生的共轭双键;减缓体系在热塑化过程中扭矩的上升速率;减少PVA热加工过程中黄度增加速率;同时使PVA力学性能得到改善。     

改性聚乙烯醇的热塑成型性能研究

聚乙烯醇(PVA)是多羟基线型高分子,含有大量氢键。分子结构规整,结晶度高,熔点高达230℃。用复配增塑剂和稳定剂对PVA进行改性,并通过DSC和FTIR测试研究了改性剂对PVA热塑成型性能的影响。结果表明:添加适量改性剂的PVA其热塑成型性能得到明显改善。     

PVA/TPU共混材料热塑加工性能及相容性的研究

采用热塑加工方法制备了聚乙烯醇/热塑性聚氨酯(PVA/TPU)共混材料,系统研究了共混材料的热塑加工性能、相容性及力学性能。结果表明:TPU的引入对共混材料的熔点影响不大,但其与PVA间的氢键作用可屏蔽PVA的羟基,较大幅度地提高了PVA初始热分解温度,获得更宽的热塑加工窗口;引入适量的TPU还可降低共混材料的熔体黏度,改善材料的热塑加工性能,另外,还可获得良好的材料相容性;随着TPU用量的增加,共混材料的拉伸强度先增后降,并在TPU用量为50 phr时达到最大值。     

Evaporation behaviour of water and its plasticizing effect in modified poly(vinyl alcohol) systems

Several modified poly(vinyl alcohol) (PVA) systems with various plasticizers were prepared and their melt‐processing was successfully realized. This paper focuses on the study of the evaporation behaviour of water in these modified PVA systems, exploring its plasticizing mechanism by using differential scanning calorimetry. The evaporation characteristics of bulk water, water in aqueous solutions of the plasticizers, and the thermal properties of PVA were also studied. The experimental results show that water in aqueous solutions of glycerol and/or caprolactam evaporates at a lower temperature than bulk water, but water in the PVA/water system evaporates at a higher temperature, with a wider DSC peak due to the interaction between water and PVA. Incorporation of glycerol, caprolactam or their mixtures further strengthens the interactions between water and the other components, retarding water evaporation. During the processing, the less closely associated water has the plasticizing effect through molecule movement, while the strongly bound water, which breaks the intermolecular hydrogen bonding of PVA and decreases its intermolecular interaction, is more beneficial to the melt‐processing of PVA. Copyright © 2003 Society of Chemical Industry     

Thermal processability and properties of highly filled poly(vinyl alcohol)/talc composite

Abstract

A highly filled PVA/talc composite was prepared through our invented thermal processing technology without using any coupling agent or compatibiliser. The results showed that compared with neat PVA, the melt temperature of the composite decreased and the degradation temperature increased, providing a big temperature window for thermal processing of PVA/talc composite. The composite melt exhibited shear thinning behaviour while its viscosity increased with increasing talc, still satisfied the requirement of thermal processing. The morphology analysis confirmed that talc was well dispersed in PVA, improving heat deflection temperature (HDT), tensile strength and modulus of PVA. When talc was 50 wt-%, the HDT, tensile strength and modulus of the composite were 115°C, 48 MPa, 1·23 GPa respectively, increased by 92, 16 and 150%, compared with PVA, and the elongation at break was 100% of the composite, confirming that the high filled PVA/talc composite was a novel PVA based material with excellent thermal and mechanical properties.