纳米二硫化钼对聚乳酸等温结晶行为的影响

采用熔融共混法制备聚乳酸/二硫化钼(PLA/MoS_2)纳米复合材料。通过差示扫描量热法(DSC)研究纳米MoS_2含量对PLA等温结晶行为的影响,采用Avrami方程分析纳米复合材料的等温结晶动力学,并采用X射线衍射(XRD)测试材料的结晶结构。由等温结晶动力学计算结果可知,加入MoS_2纳米粒子后,PLA基体的结晶速率显著提高。例如,当结晶温度(Tc)为110℃,MoS_2含量由0增至2.0%时,试样的结晶半时间(t1/2)可由纯PLA的8.5 min大幅降低至3.2 min。而当Tc为120℃,MoS_2含量由0增至2.0%时,试样的t1/2由纯PLA的11.4 min降低至3.8 min。同时,随着MoS_2含量的增大,PLA基体的最大结晶度也有一定程度增大,说明MoS_2起到异相成核剂作用。PLA/MoS_2试样的Avrami指数在2.6~3.1之间,可知在MoS_2存在下,PLA晶体主要为异相成核和三维生长。     

癸二酸二苯甲酰肼对PLA等温结晶行为及拉伸性影响

采用熔融共混法制备聚乳酸/癸二酸二苯甲酰肼(PLA/SBH)共混物。通过差示扫描量热(DSC)分析研究成核剂SBH添加量以及等温温度对PLA熔体等温结晶行为的影响。由结晶动力学分析可知,随着SBH添加量增大,PLA半结晶时间大幅缩短,结晶速率显著加快。加入SBH后,Avrami指数在2.51~3.14之间,PLA熔体结晶以异相成核为主,晶体生长为三维生长。对于PLA急冷模压样条,结晶度仅为2.9%。而加入1.0份SBH后,PLA熔体在134℃下经过3 min等温结晶处理后,所得PLA/SBH(100/1.0)模压样条结晶度达到42.0%。相对于急冷PLA样条,经过热处理的PLA/SBH(100/1.0)样条的维卡软化点由64.3℃大幅提升至160.6℃,而拉伸强度也有所增大。     

稀土成核剂对聚乳酸非等温行为的影响

利用差示扫描量热仪(DSC)研究了3种稀土成核剂[WBG-Ⅱ、WBG-Ⅱ(a)与WBG-Ⅱ(b)]对聚乳酸(PLA)的影响。非等温结晶动力学分析表明:添加成核剂后在相同的降温速率下结晶发生的温度区间比纯PLA高11～15℃,其中WBG-Ⅱ(b)在10℃/min的降温速率下可以将PLA的结晶温度由109.2℃提高到124.1℃,结晶诱导时间tinc由8.43 min减少到6.55 min,说明可以作为1种有效的PLA成核剂。     

聚乳酸（PLA）／三醋酸甘油酯（TAc）的结晶性能研究

用三醋酸甘油酯（TAc）增塑聚乳酸（PLA）,研究了TAc对PLA在不同温度结晶时的结晶性能的影响。随着TAc的添加,PLA的结晶度与其球晶生长速率逐渐增加,断裂伸长率增大,抗张强度降低。TAc的最佳添加量为25％。研究不同温度等温结晶时PLA/TAc的机械性能以及晶体形态的影响,发现结晶温度升高,PLA/TAc的球晶生长速率减小,抗张强度增大,断裂伸长率降低。     

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,...     

偶联改性棉花纳米纤维素/聚乳酸复合材料的非等温结晶性能和疏水性能研究

采用偶联剂3-氨丙基三乙氧基硅烷(KH550)对棉花纳米纤维素(CNF)进行表面改性,得到偶联改性棉花纳米纤维素(cCNF),将cCNF与聚乳酸(PLA)的氯仿溶液直接共混,通过溶液浇铸得到偶联改性棉花纳米纤维素/聚乳酸复合材料(cCNF/PLA)。研究cCNF的加入量对PLA的非等温结晶性能和疏水性能的影响。结果表明:复合材料的结晶峰温度及结晶度先升高后降低,当cCNF的添加量为0.125%时,复合材料结晶峰温度及结晶度升高至最大值,分别为107.2℃、32.1%,比纯PLA分别升高2.4℃、5.5%;PLA及其复合材料的半结晶时间(t_(1/2))也缩短。采用改进的Avrami方程研究PLA及cCNF/PLA的非等温结晶过程,在2、4、6℃/min的降温速率下,n值的范围为1.85～2.54,表明晶体的生长模式为二维和三维并存,当cCNF的添加量为0.125%时,结晶速率常数均升高到最大值。当cCNF的添加量为1%时,cCNF/PLA复合材料的接触角降到最小值69°,比纯PLA降低11.5°。     

碳纳米管/聚乳酸复合材料非等温结晶动力学

研究了聚乳酸(PLA)与多壁碳纳米管(MWNTs)/PLA复合材料的非等温结晶动力学。利用硅烷偶联剂KH-550改性碳纳米管,并用溶液共混法制备MWNTs/PLA复合材料。利用DSC研究了材料的结晶过程,所得的降温曲线表明基体中的碳纳米管可以提高材料的结晶温度范围和结晶放热焓。采用Jeziorny法和Mo法研究了PLA与MWNTs/PLA复合材料的非等温结晶动力学,结果表明,适量的碳纳米管有效地起到了成核剂的作用,提高了材料的结晶速率。     

聚己内酯对聚乳酸熔融结晶的影响

聚合物共混材料的结晶行为对材料性能有重要的影响,结晶行为是共混材料研究的主要问题。选用聚乳酸(PLA)和聚己内酯(PCL)共混材料,采用偏光显微镜和差示扫描量热仪,对PLA/PCL共混材料的结晶行为进行研究。通过等温结晶动力学,分析PCL对PLA在100和120℃时等温结晶的影响。结果表明,PCL相作为异相成核剂加入PLA相,使得PCL/PLA共混物中异相结晶成核效率提高,晶体直径减小,半结晶时间减小,提高PCL/PLA共混物的结晶能力。随着PCL相的占比增大,PCL/PLA(40/60)试样中出现"海-岛结构",异相成核效率增大,半结晶时间较小,结晶直径减小,结晶度减小。     

微型注塑条件下PLA/POM共混物的形貌及结晶行为

采用微型注塑加工技术制备了聚乳酸(PLA)/聚甲醛(POM)共混物微型注塑试样,利用扫描电子显微镜(SEM)、差示扫描量热(DSC)仪和偏光显微镜(PL M)研究了微注塑加工过程中注射速率和模具温度对PLA/POM微型注塑试样的形貌及结晶行为的影响。结果表明,微型注塑加工条件下,PLA/POM共混物为相容体系;注射速率对POM的结晶行为影响更大,提高注射速率更有利于POM分子链的取向及取向程度的增加,导致POM的熔点和PLA/POM共混物微型注塑试样的结晶度提高;提高模具温度明显增加PLA的热焓松弛峰温度,同时还导致PLA冷结晶温度和熔点的降低以及POM熔点的增加,这与较高模温条件下PLA分子链较易规整排列以及PLA较高的玻璃化转变温度有关。此外,PLA/POM共混物微型注塑试样中PLA形成的晶体类型与等温结晶的温度有关,相对较低温度的等温结晶条件有利于PLA/POM共混物微型注塑试样形成环带球晶。微型注塑条件下,PLA/POM共混物微型注塑试样的中PLA形成的晶体类型与冷却方式有关。     

聚乳酸/四针状氧化锌晶须非等温冷结晶行为的研究

采用熔融共混法制备了聚乳酸(PLA)/四针状氧化锌晶须(T-ZnOw).用差示扫描量热仪研究了PLA及PLA/T-ZnOw的非等温冷结晶行为;用Jeziorny法和Mo法对其非等温冷结晶动力学进行了分析研究,并计算了相关的结晶动力学参数.结果表明,Jeziorny法和Mo法均能很好地描述PLA及PLA/T-ZnOw的非等温冷结晶过程,且结果一致.Jeziorny法分析表明,初次结晶阶段PLA及PLA/T-ZnOw的Avrami指数n1值范围分别为4.22～5.43和3.11～4.80,而二次结晶阶段的Avrami指数n2值范围分别为3.10～4.66和2.69～5.57,说明T-ZnOw的加入改变了PLA的成核和晶体生长规律.Mo法分析表明,在相同的X(t)下,PLA/T-ZnOw的F(T)值整体大于PLA,T-ZnOw的加入降低了PLA的结晶速率.偏光显微镜观察结果显示,随着T-ZnOw的加入,PLA球晶尺寸减小,数目增多,T-ZnOw促进了PLA的成核.     

聚乳酸在二氧化碳作用下的冷结晶

利用差示扫描量热仪研究了聚乳酸（PLA）在常压下的等温冷结晶行为,并用偏光显微镜观测了不同温度下等温结晶100 min的PLA样品的结晶形态;以二氧化碳（CO2）为介质,利用高压釜在5 MPa压力、不同温度下制备了冷结晶过程中的等温结晶100 min的PLA样品,分别利用偏光显微镜和广角X射线衍射仪对比了常压和CO2作用下PLA产生的球晶形态和晶型结构。结果表明,CO2对PLA有显著的增塑作用,可以增强PLA分子链的活性,使其在较低的温度下发生冷结晶;与常压相比,PLA在CO2作用下冷结晶形成的球晶尺寸减小球晶数量增加球晶完善程度提高,但最终结晶度降低。     

Comparative study on quiescent crystallization kinetics of isotactic polyolefins

Quiescent melt crystallization rates of various polyolefins including high density polyethylene (PE), isotactic form of polypropylene (PP), polybutene‐1 (PB1), and poly(4‐methyl pentene‐1) (P4MP1) were investigated under both isothermal and nonisothermal conditions using differential scanning calorimetry (DSC). The order of overall crystallization rates under quiescent conditions from fast to slow was found to be: PE, P4MP1, PP and PB1. The Avrami equation was used to analyze isothermal and nonisothermal crystallization processes, respectively. In order to compare relative crystallization rates of these polymers, continuous cooling transformation curves for each polymer under nonisothermal condition as well as the plot of crystallization half‐time as a function of crystallization temperature under isothermal conditions were constructed. Comparisons were made of the relative rate of crystallization of the different isotactic polyolefins with each other and with reports in the literature. Isotactic polyolefins with linear side groups crystallize increasingly more slowly as the side group lengthens with polypentene‐1 (PPT1) and polyhexene‐1 (PH1) crystallizing even more slowly than PB1. It is notable that P4MP1, which has isobutyl as a bulky side group, and apparently poly(3‐methyl butene‐1) (P3MB1) showed fairly high crystallization rates. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Thermal properties and non‐isothermal crystallization behavior of poly(trimethylene terephthalate)/poly(lactic acid) blends

Thermal properties and non‐isothermal melt‐crystallization behavior of poly(trimethylene terephthalate) (PTT)/poly(lactic acid) (PLA) blends were investigated using differential scanning calorimetry and thermogravimetric analysis. The blends exhibit single and composition‐dependent glass transition temperature, cold crystallization temperature (T_cc) and melt crystallization peak temperature (T_mc) over the entire composition range, implying miscibility between the PLA and PTT components. The T_cc values of PTT/PLA blends increase, while the T_mc values decrease with increasing PLA content, suggesting that the cold crystallization and melt crystallization of PTT are retarded by the addition of PLA. The modified Avrami model is satisfactory in describing the non‐isothermal melt crystallization of the blends, whereas the Ozawa method is not applicable to the blends. The estimated Avrami exponent of the PTT/PLA blends ranges from 3.25 to 4.11, implying that the non‐isothermal crystallization follows a spherulitic‐like crystal growth combined with a complicated growth form. The PTT/PLA blends generally exhibit inferior crystallization rate and superior activation energy compared to pure PTT at the same cooling rate. The greater the PLA content in the PTT/PLA blends, the lower the crystallization rate and the higher the activation energy. Moreover, the introduction of PTT into PLA leads to an increase in the thermal stability behavior of the resulting PTT/PLA blends. Copyright © 2011 Society of Chemical Industry     

剪切应力对聚乳酸结晶性能的影响

通过改变升降温循环次数、热历史消除时间及温度,研究了剪切作用力对聚乳酸树脂原料及流延片结晶行为的影响规律。结果表明,聚乳酸的结晶行为受其分子的缠结状态或相对有序程度的影响,在剪切作用力的影响下,聚乳酸分子解缠结或者相对有序程度提高,因此更容易出现冷结晶过程。     

聚乳酸/可反应性纳米SiO2复合材料的等温结晶动力学

采用熔融共混法制备了聚乳酸/可反应性纳米二氧化硅(PLLA/RNS)复合材料。利用差示扫描量热仪研究了RNS对PLLA等温结晶行为的影响;用Avrami 方程研究了PLLA及其复合材料的等温结晶动力学。结果表明,加入RNS对PLLA结晶起到了异相成核作用,随着RNS含量的增加,PLLA的结晶速率(K)提高,半结晶时间(t1/2)减小,而Avrami指数(n)变化不大,说明RNS没有改变PLLA结晶的成核机理;利用Arrhenius方程和Lauritzen-Hoffman理论分别对PLLA及其复合材料的结晶活化能(ΔE)、成核参数(Kg)和折叠链端表面自由能(σe)进行计算后发现,复合材料的ΔE比纯聚乳酸的小,Kg 、σe略有增加。这表明加入RNS降低了复合材料的ΔE,从而有效地促进了PLLA基体的结晶。     

Thermal, rheological, and mechanical properties of polylactide/poly(diethylene glycol adipate)

Polylactide (PLA) was plasticized with a new biodegradable macromolecular plasticizer-poly(diethylene glycol adipate) (PDEGA). The crystallization behavior, miscibility, rheological behavior, mechanical properties and phase behavior of PLA/PDEGA blends were investigated. The PDEGA lowered the glass transition temperature and the cold crystallization temperature. With an increase of PDEGA content, the break strain and impact strength increased significantly. The high break strain of 480 % and the high impact strength of 30 kJ/m² were obtained for 70/30 PLA/PDEGA blend. PDEGA was uniformly dispersed in the PLA matrix. The results indicated that PDEGA had a good plasticizing effect on PLA.     

Melting behavior,isothermal and nonisothermal crystallization kinetics of EPPE/mLLDPE blends

Melting behavior and crystallization kinetics of easy processing polyethylene (EPPE) and the blends of EPPE/mLLDPE were studied using differential scanning calorimetry at various crystallization temperature and cooling rates. The Avrami analysis was employed to describe the isothermal and nonisothermal crystallization process of pure polymers and their blends, and a method developed by Mo was applied for comparison. Kinetic parameters such as the Avrami exponent (n), the kinetic crystallization rate constant (k and k_c), the peak temperatures (T_p), and the half-time of crystallization (t_1/2), etc. were determined. The appearance of double melting peaks and the double crystallization peaks of the polymers showed that the main chain and the branches crystallize seperately, but the main chains of two polymers can crystallize together and mLLDPE act as nuclei while EPPE crystallizes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synergistic effects of shear flow and nucleating agents on the crystallization mechanisms of Poly (Lactic Acid)

This paper presents a study of the effects of microscopic particles of talc on the crystallization kinetics of PLA. Our study covers the quiescent conditions and the case where a shear flow is applied “short term shearing”. The incorporation of talc increases the crystallization rate; it enhances the nucleation mechanism through additional heterogeneous nuclei. The microstructure is highly affected by the addition of talc due to the increase of the number of nuclei (i.e. reduced crystalline size). The application of a shear flow increases the ability of PLA to crystallize even in the presence of talc particles. The impact of shear rate becomes dramatically important just after a critical shear rate of 0.1 s^?1. It turns out that the shear rate enhances more the crystallization of PLA with talc than the pure PLA under quiescent conditions. Consequently, a supplementary contribution “synergistic effects” is responsible of the relative enhancement of the crystallization of PLA in the presence of shear flow and talc. With combining different experimental analysis techniques and modeling of the crystallization kinetics, the synergistically effects were quantified in terms of the nucleation density induced by the mutual interaction between shear flow and particles.     

几种用于3D打印的高分子材料的性能对比

以2种商用3D打印材料(2种PLA)为主要研究对象,同时选取了2种性能相近的高分子材料(PP、POM),分别对其热性能、结晶性能和流变性能进行了表征。实验结果表明,PLA、PP、POM的分解温度均大于300℃,因此,在3D打印的温度下,均不会发生降解;PLA、PP、POM均属于非牛顿流体,POM的非牛顿指数n值相对较大,更接近牛顿流体;PLA的Eη最大,流动相对困难。在DSC降温测试过程中,当降温速率较低时,PLA才会结晶,但PP和POM结晶相对容易。结晶动力学结果表明,Ozawa理论适用于2#PLA和PP,而并不适用于POM。将1#PLA与3#PP进行3D打印测试,结果表明,3#PP翘曲现象严重,可在PP中添加粉体,满足3D打印需要。     

Quantification of the distribution of carbon black in natural rubber/polybutadiene blends by differential scanning calorimetry

The distribution of carbon black (CB) in uncured blends of natural rubber (NR) and polybutadiene (PB) can be quantified using DSC. The crystallization temperature of PB containing CB, measured during cooling from the melt, increases with the CB loading. This phenomenon was used to calculate the CB content in PB and conversely in NR in NR/PB/CB mixtures. Two different blends containing N550 CB were studied. A deeper analysis was performed over the entire composition range of NR/PB blends filled with N234 CB. Two different trends were highlighted depending on composition. Below 50 wt% of NR in the elastomer phase, the crystallization temperature of PB is higher than that of pure PB indicating that a part of the CB is dispersed in PB. Above 50 wt% of NR, the crystallization temperature of PB is lower than that of pure PB, indicating that the whole CB is in the NR phase and that fractionated crystallization of PB simultaneously occurs. Both phenomena are consistent as the dispersed phase morphology is favored by a large increase of the matrix viscosity by the filler. For both CBs, the results indicate that CB has larger affinity for NR than for PB. This tendency was confirmed by transmission electron microscopy. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers