聚乳酸注塑结晶性能研究

采用有机成核剂TMC与无机成核剂滑石粉对聚乳酸进行改性,以为熔融焓为指标研究了其在注塑成型过程中的结晶行为。结果表明:(1)有机成核剂TMC相对无机滑厂粉对聚乳酸的成核促进作用更好,添加量更小,更有利于提升聚乳酸的耐温性能;(2)在一定取值范围内当模具温度为100℃模具内停留时间60 s时聚乳酸可以很好地结晶,并具有最佳的成型效率;(3)随着聚乳酸结晶度(熔融焓)的增加,材料的拉伸强度增加,而冲击强度降低。     

滑石粉、碳酸钙填充聚丙烯复合材料等温结晶行为的研究

用熔融共混法分别制备了聚丙烯(PP)/滑石粉、PP/碳酸钙(CaCO3)复合材料,用差示扫描量热法考察了PP及其复合材料的等温结晶过程,并用Avrami方程对纯PP及PP/滑石粉、PP/CaCO3复合材料的等温结晶动力学行为进行了分析。结果表明,PP、PP/滑石粉及PP/CaCO3复合材料的Avrami指数均小于2.3,存在均相成核和异相成核双重成核机理,且其结晶速率常数和结晶速率均随着结晶温度的升高而减小;在该体系中,滑石粉对基体PP有明显的异相成核作用,使PP的结晶速率加快、结晶时间缩短;而CaCO3则没有明显的异相成核作用。     

滑石粉、碳酸钙填充聚丙烯复合材料等温结晶行为的对比研究

用熔融共混法分别制备了聚丙烯（PP）/滑石粉、PP/碳酸钙(CaCO3)复合材料,用差示扫描量热法(DSC)考察了PP及其复合材料的等温结晶过程,并用Avrami方程对纯PP及PP/滑石粉、PP/CaCO3复合材料的等温结晶动力学行为进行了分析。结果表明,PP、PP/滑石粉及PP/CaCO3复合材料的Avrami指数均小于2.3,存在均相成核和异相成核双重成核机理,且其结晶速率常数和结晶速率均随着结晶温度的升高而减小;在该体系中,滑石粉对基体PP有明显的异相成核作用,使PP的结晶速率加快、结晶时间缩短;而CaCO3则没有明显的异相成核作用。     

多种成核剂对PBS结晶及力学性能的影响

本文研究了滑石粉、TMB-5、碳酸钙、硫酸钙晶须、高岭土等五种成核剂对聚丁二酸丁二醇酯(PBS)结晶行为及力学性能的影响。偏光显微镜的观察结果显示了成核剂能细化PBS的球晶尺寸,提高球晶排列的规整度;热分析结果表明添加成核剂能提高PBS的结晶温度,加快PBS的结晶速率;结晶性能的改善又直接造成PBS力学性能的提高,其拉伸强度和冲击强度都有明显上升。五种成核剂中以滑石粉的效果最为突出,能使PBS的结晶温度上升11℃,拉伸强度提高了4.4MPa。     

碳纤维增强聚酰胺6复合材料的结晶行为研究

通过偏光显微镜和差示扫描量热仪(DSC)研究了碳纤维(CF)和滑石粉对聚酰胺6(PA6)结晶行为的影响。结果表明,CF的加入在PA6和CF的界面诱发横晶,CF和滑石粉在PA6基体中起到了异相成核作用,改变PA6的成核机理和晶体生长方式,提高了起始结晶温度和结晶速率。结晶速率随普等温结晶温度的升高而下降。当冷却速率增大时,起始结晶温度下降,结晶度增大。     

滑石粉对聚乳酸的影响

研究了不同含量滑石粉对高光纯聚乳酸结晶性能以及综合力学性能的影响,采用差示扫描量热法研究了滑石粉对聚乳酸非等温结晶行为的影响,并使用X-射线衍射仪和热台偏光显微镜对聚乳酸/滑石粉共混物的晶型变化情况以及等温结晶过程进行了观察研究。结果表明:聚乳酸结晶峰温度随着滑石粉含量的增加而提高,且结晶温区不断向高温方向移动,结晶速率也随之加快。相比于纯聚乳酸,当滑石粉的质量分数为10%时,聚乳酸的结晶峰温度提高了13.7 K,拉伸强度从58.6 MPa提高至72.0 MPa,断裂拉伸应变从2.7%提高至4.6%,弯曲强度从88.9 MPa提高至104.0 MPa,弯曲模量从3 589 MPa提高至4 837 MPa。同时,滑石粉的加入不会改变聚乳酸的晶型,但会使得聚乳酸球晶的尺寸明显变小,晶核密度明显增加。     

成核剂对尼龙66等温结晶行为的影响

用差示扫描量热法(DSC)测定了滑石粉、氟化钙等成核剂对尼龙66等温结晶行为的影响。结果表明,尼龙66.M成核剂体系在高温结晶时存在晶型转变;Avrami指数n、成核机理、晶体生长方式基本上不受成核剂的影响。少量成核剂可使结晶成核自由能降低,结晶速率加大,其中滑石粉的效果最为显著。     

苯基磷酸锌对聚乳酸结晶行为影响的研究

采用DSC,POM研究了成核剂苯基磷酸锌（PPZn）对聚乳酸结晶行为的影响。结果表明：PPZn可以作为聚乳酸的高效成核剂,PPZn的加入显著提高了聚乳酸的结晶速率和结晶度。当PPZn的质量分数为5％0时TCs（起始结晶温度）降低了约24℃,TCe（终止结晶温度）降低了约29℃。PPZn的加入使聚乳酸的半结晶时间大大缩短。当PPZn的质量分数为2％时,结晶速率常数增大约5个数量级。     

成核剂对聚乳酸挤出流延膜结晶性能的影响

聚乳酸作为一种优异的可降解塑料近年来发展迅速,受PLA结晶性速度慢,脆性高的影响,改善PLA结晶性能的研究日益受到关注。本文研究了两种成核剂对挤出流延PLA结晶性能的影响。实验结果显示,挤出流延的PLA薄膜的结晶度仍然很低,在升温过程有明显的冷结晶行为,成核剂对PLA结晶的贡献远低于冷却速度的影响。相较于TMC300,使用滑石粉(Talc)作为成核剂,能更快提升PLA的结晶速率,提升结晶完善性。挤出流延的PLA膜还需要经过退火处理使结晶完善,释放加工过程的取向内应力。使用两种成核剂的样品大约经过20分钟的热处理即可完成结晶,在退火过程,Talc显示出更为优越的结晶加速行为。因此相较而言,Talc更适合在PLA挤出流延制膜中应用。     

含较高立构缺陷聚乳酸的非等温结晶动力学

用非等温结晶动力学研究了聚乳酸(PLA)的结晶行为,利用Hoffman-Weeks外推法以及Baur等提出的方程反推出PLA中的右旋组分摩尔分数为7.2%.较高的右旋组分摩尔分数是PLA结晶过程中成核速率低的主要因素.添加质量分数为2%滑石粉等成核剂后,PLA结晶速率没有明显提高;含10%滑石粉的PLA结晶速率略上升,...     

聚乳酸的等温结晶研究

研究了成核剂SX,滑石粉（Talc）及SX与Talc复合对聚乳酸（PLA）结晶的影响。等温结晶动力学表明,各个体系Avrami参数均在1—2．5之间,为异相成核。SX含量从0．2％（质量分数,下同）增加到0．6％后,结晶速率大大提高,结晶半周期tln为0．65min,并且随着等温结晶温度的减小,t1/2减小。Talc含量变化对提高PLA结晶速率没有明显影响。SX是比Talc更高效的成核剂,当其添加到0．6％,120oC时等温t1/2为0．65min,远小于添加6％Talc的。SX与Talc有协同作用,添加0．2％SX＋4％Talc的样品t1,2达到0．10min。     

退火对聚乳酸结晶及耐热性能的影响

以活化海泡石(ADI-S)为成核剂,通过熔融混合的方法制备了聚乳酸(PLA)/ADI-S复合材料。采用差示扫描量热仪、广角X射线衍射仪、偏光显微镜和热变形、维卡软化点温度测定仪分析了退火条件对PLA结晶性能及耐热性能的影响。结果表明,添加成核剂后,短时间内的退火可大幅提高PLA的结晶度和耐热性能;PLA/ADI-S在90 ℃退火10 min时,其结晶度为53.3 %,维卡软化点为83.3 ℃。     

Crystallization morphology and crystallization kinetics of poly(lactic acid): effect of <Emphasis Type="Italic">N</Emphasis>-Aminophthalimide as nucleating agent

The effect of N-Aminophthalimide compound (NA-S) as nucleating agent on crystallization behavior and morphology of poly(lactic acid) was studied. With polarized optical microscope (POM), the unique phenomena of nucleation and epitaxial crystallization of PLA/NA-S system were observed. Dynamic morphology of crystallization was also studied by POM to investigate the relationship between growth behavior of PLA and nucleating agent. Isothermal and non-isothermal crystallization behavior of PLA were studied by differential scan calorimeter (DSC). When nucleating agent was added, a new peak appeared in wide angle X-ray diffraction (WAXD) compared with pure PLA, indicating the nucleating effect of NA-S on crystallization of PLA. All the results indicate that the nucleating agent of NA-S shows obvious nucleating effect on isothermal crystallization above 120 °C and in non-isothermal crystallization after it is added in PLA, that is, the induction crystallization time is reduced, the crystallization rate and nucleation density of PLA are increased.     

原位聚合法制备聚乳酸/滑石粉复合材料

用硅烷偶联剂对超细滑石粉（Talc）改性后,采用原位聚合法制备出不同质量分数的聚乳酸/滑石粉（PLA/Talc）复合材料,并采用傅里叶变换红外光谱仪（FTIR）、扫描电子显微镜（SEM）、核磁共振波谱仪（NMR）、热失重分析仪（TG）、偏光显微镜（POM）等方法对复合材料进行表征。结果表明,Talc粒子在复合材料中均匀分散;PLA/含量3 %Talc的复合材料的拉伸强度、冲击强度分别比纯PLA增加了102.56 %和47.83 %,复合材料的热稳定性也明显提高;Talc促进了PLA结晶性能,在一定程度上提高其力学性能,复合材料降解速率比于纯PLA明显加快。     

Effect of nucleating agents on the crystallization behavior and heat resistance of poly(l‐lactide)

Poly (l ‐lactide) (PLLA) blends with various nucleators were prepared by melt processing. The effect of different nucleators on the crystallization behavior and heat resistance as well as thermomechanical properties of PLLA was studied systematically by differential scanning calorimetry, X‐ray diffraction, heat deflection temperature tester, and dynamic mechanical analysis. It was found that poly(d ‐lactide), talcum powder (Talc), a multiamide compound (TMC‐328, abbreviated as TMC) can significantly improve the crystallization rate and crystallinity of PLLA, thus improving thermal–resistant property. The heat deflection temperature of nucleated PLLA can be as high as 150°C. The storage modulus of nucleated PLLA is higher than that of PLLA at the temperature above T_g of PLLA. Compared with other nucleating agents, TMC was much more efficient at enhancing the crystallization of PLLA and the PLLA containing TMC showed the best heat resistance. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42999.     

Effect of annealing and orientation on microstructures and mechanical properties of polylactic acid

Two types of polylactic acid (PLA) films (one amorphous and one semi‐crystalline) were produced by sheet extrusion. Talc was used as a nucleation agent for the semi‐crystalline PLA. The films were annealed above their T_g or were uniaxially orientated in two ways: (1) via a drawing system in front of the extruder and die or (2) via a three‐roller stretching system. The slower crystallization rate and lower melting stress of the PLA resulted in amorphous film using the drawing system. Annealing above T_g increased crystallinity and polymer chain relaxation, which resulted in increases in both strength and toughness. Stretching above T_g also produced simultaneous crystallization and chain relaxation, which resulted in increases in both modulus and toughness. Both modulus and tensile strength in the stretching direction were higher than in the crosswise direction. Talc acted not only as a rigid filler to reinforce the PLA, but also as a nucleation agent for the PLA, especially during annealing. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Effect of sepiolite on the crystallization behavior of biodegradable poly(lactic acid) as an efficient nucleating agent

To enhance the crystallization kinetics of poly(lactic acid) (PLA), fibrous sepiolite was explored for nucleating the crystallization of PLA. PLA/sepiolite nanocomposites were prepared via the melt‐extrusion method. The effect of sepiolite on the crystallization behavior, spherulite growth and crystal structure of PLA were investigated by means of differential scanning calorimetry (DSC), polarized optical microscope (POM), wide angle X‐ray diffraction (WAXD), Fourier transform infrared (FTIR), and scanning election microscope (SEM). On the basis of DSC and POM results, the overall crystallization kinetics of PLA/sepiolite nanocomposites were significantly enhanced leading to higher crystallinity and nucleation density, faster spherulite growth rate (G) and lower crystallization half‐time (t_1/2) compared with the neat PLA. Under non‐isothermal conditions, the PLA blend comprising 1.0 wt% of sepiolite still revealed two crystallization peaks upon cooling at a rate of 35°C/min. Above phenomena strongly suggested that sepiolite was an effective nucleating agent for PLA. FTIR and WAXD analyses confirmed that the crystal structure of PLA matrix was the most common α‐form. SEM micrographics illustrated the fine three‐dimensional spherulite structures with the lath‐shape lamellae regularly arranged in radial directions. POLYM. ENG. SCI., 55:1104–1112, 2015. © 2014 Society of Plastics Engineers     

Crystallization of poly(lactic acid) accelerated by cyclodextrin complex as nucleating agent

Poly(lactic acid) (PLA) is a well-known biodegradable and biocompatible polyester with intrinsically slow crystallization rate. To extend its applications to the field where heat resistance is required, increasing the crystallization rate of the material becomes critical. In this note, the nucleation effect of supramolecular inclusion complex (IC), organized by non-covalent interactions through threading α-cyclodextrin molecules onto PLA chains, on the crystallization of PLA was investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The formation of IC was confirmed by wide-angle X-ray diffraction and DSC measurements. It was found that the presence of PLA-IC significantly promoted the crystallization of PLA from both the non-isothermal and isothermal crystallization experiments. The nucleation mechanism was also discussed to some extent.     

Fast crystallization of poly(3‐hydroxybutyrate) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) with talc and boron nitride as nucleating agents

The crystallization behavior of poly(3‐hydroxybutyrate) (PHB) and poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) induced by two kinds of nucleating agents, boron nitride (BN) and talc, was investigated by differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. Both BN and talc have good nucleating ability in the crystallization of PHB and PHBV. From these results, combined with molecular weight measurement by gel permeation chromatography, the mechanism of nucleation by BN and talc in the crystallization of PHB and PHBV has been proposed. BN acts as a nucleating agent itself and initiates nucleation in the crystallization of PHB and PHBV. Talc acts in a different way. It reacts as a chemical reagent with the molten chains of PHB/PHBV, while the reaction product acts as the true nucleating agent, which lowers the crystallization barriers of PHB and PHBV. ¹H NMR spectroscopy provides evidence for the reaction between PHB and talc and supports the proposed nucleation mechanism. Copyright © 2005 Society of Chemical Industry     

Crystallization behavior and nucleation analysis of poly(l‐lactic acid) with a multiamide nucleating agent

To accelerate the crystallization of poly(L ‐lactic acid) (PLLA) and enhance its crystallization ability, a multiamide nucleator (TMC) was introduced into the PLLA matrix. The thermal characteristics, isothermal and nonisothermal crystallization behavior of pure PLLA and TMC‐nucleated PLLA were investigated by differential scanning calorimetry. The determination of thermal characteristics shows that the addition of TMC can significantly decrease the onset temperature of cold crystallization and meanwhile elevate the total crystallinity of PLLA. For the isothermal crystallization process, it is found that the overall crystallization rate is much faster in TMC‐nucleated PLLA than in pure PLLA and increases as the TMC content is increased, however, the crystal growth form and crystalline structure are not influenced much despite the presence of TMC. In the case of nonisothermal crystallization, the nucleation efficiency and nucleation activity were estimated and the results indicate that excellent nucleation‐promoting effect could be achieved when the weight percentage of TMC is chosen between 0.25% and 0.5%. Polarized optical microscopy observation reveals that the nuclei number of PLLA increases and the spherulite size reduces greatly with the addition of TMC. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers