一种非等温结晶动力学研究方法在聚丙烯中的应用

针对修正的Avrami方程处理聚合物非等温结晶过程中出现的线性拟合不理想及不能获得可靠动力学参数的缺点,提出了一种新方法处理聚合物非等温结晶过程,成功用于聚丙烯非等温结晶的动力学处理,克服了Avrami方程处理过程中的线性回归不够理想的状况,同时也明确了结晶度在非等温结晶过程中的影响规律。     

PA1212的结晶动力学研究

采用DSC方法研究了PA1212的非等温和等温结晶动力学。Avrami方程可以适用PA1212的等温结晶过程,其Avrami指数为2．51～2．87,等温结晶活化能为-131．9 kJ/mol;在非等温结晶过程中,结晶速率随降温速率的增大而提高,综合利用Avrami方程和Ozawa方程得到Avrami指数与Ozawa指数的比值为1．31～1．49,非等温结晶活化能为-87．96 kJ/mol。结果表明,与其他聚酰胺相比,PA1212较容易结晶。     

聚酰胺11/白炭黑纳米复合材料的非等温结晶动力学研究

采用原位聚合法制备了聚酰胺11（PA11）及PA11/白炭黑纳米复合材料,利用差示扫描量热仪研究了PA11及其纳米复合材料的非等温结晶过程,用经Jeziorny修正的Avrami方程、Mo法对其非等温结晶动力学进行了研究,计算并得到了非等温结晶动力学参数。结果表明,Avrami方程和Mo法都适用于处理PA11及其纳米复合材料的非等温结晶过程;在其非等温结晶过程中,PA11及其纳米复合材料都包括初期结晶和二次结晶两个阶段;Mo法表明,复合材料的结晶速率比PA11的小。此外,用Huffman-Lauritzen理论计算了PA11及其纳米复合材料非等温结晶的结晶活化能,结果表明,纳米复合材料的结晶活化能的绝对值小于PA11。     

聚合物等温结晶动力学研究的一种新方法

基于多年对聚合物结晶动力学研究工作的积累,提出了一种研究聚合物等温结晶动力学的新方法。针对采用Avrami方程处理聚合物结晶过程中出现的非线性、不能获得可靠动力学参数及Avrami方程参数的物理意义不明确的缺点,采用新方法处理聚合物等温结晶过程,成功用于聚丙烯等温结晶体系,既克服了Avrami方程处理过程中的线性回归不够理想的状况同,时也明确了Avrami方程参数的物理意义。     

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。     

PA1212-b-PEG嵌段共聚物的合成和非等温结晶动力学研究

采用DSC方法研究了PA1212-b-PEG在不同降温速率下的结晶过程,并利用Avrami方程研究了其非等温结晶动力学。在非等温结晶过程中,随着降温速率的增大,结晶温度向低温偏移。综合利用Avrami方程得到Avrami指数为4,说明结晶是以异相成核,三维生长。     

PA 6非等温结晶动力学研究

用差示扫描量热法研究了聚酰胺(PA)6的非等温结晶动力学,并分别用Ozawa法、Jeziorny法和莫志深方程法处理PA 6的非等温结晶行为。结果表明:Ozawa法和Jeziorny法均不能很好地描述PA 6非等温结晶过程;莫志深方程结合Avrami和Ozawa方程,可很好地描述PA 6非等温结晶过程;PA 6的结晶受温度的影响较大,一旦成核,结晶可在短时间内发展得比较完善。     

动态硫化尼龙12/丙烯酸酯橡胶热塑性弹性体的非等温结晶动力学

利用熔融共混动态硫化法制备了尼龙12/丙烯酸酯橡胶热塑性弹性体（PA 12/ACM TPV）,采用差示扫描量热仪测试了PA 12/ACM TPV和PA 12在不同降温速率下的非等温结晶行为,并分别用Ozawa和Mo方程研究了材料的非等温结晶动力学。结果表明,不同降温速率下,PA 12/ACM TPV和PA 12的结晶峰均为单峰,前者的结晶速率大于后者;Mo方程可以很好地描述PA 12/ACM TPV和PA12的非等温结晶过程,而Ozawa方程则不适合;采用Mo方程分析,PA 12/ACM TPV中橡胶相ACM的存在提高了PA 12的结晶速率。     

降解PP/EPDM共混物的非等温结晶动力学

使用过氧化二异丙苯降解聚丙烯(PP),熔融法制备降解PP与三元乙丙橡胶(EPDM)共混物,采用广角X射线衍射及差示扫描量热法分析了降解PP/EPDM共混物的晶体结构及非等温结晶动力学。结果发现:PP降解后β晶的(300)晶面消失,导致降解PP及其共混物韧性下降、晶粒的粒径分布变宽;降解PP/EPDM共混物在非等温结晶过程中有明显的快速初级结晶和缓慢的次级结晶过程,降解PP以均相成核的三维球晶方式生长,Avrami指数与Ozawa指数相等,Jeziorny方程和Ozawa方程都可以很好地描述降解PP/EPDM共混物的非等温结晶过程。     

聚丙烯/乙丙抗冲共聚物合金结晶行为研究

实验室聚合得到乙烯单元含量分别为0.94 %、1.67 %、3.00 %(摩尔分数,下同)的聚丙烯/乙丙抗冲共聚物（PP/EPR）合金样品,用差示扫描量热法研究了样品的等温结晶和非等温结晶行为。实验结果表明,各样品在不同温度下的等温结晶均符合Avrami方程;同一样品,等温结晶温度越高,结晶所需要的时间就越长,结晶速率越低,非等温结晶时随着降温速率的增加,结晶温度范围变宽并向低温移动;对于不同样品,等温结晶的结晶速率随乙烯单元含量增加而降低,但当乙烯单元含量为3.00 %时出现相反的情况,非等温结晶时的结晶温度也有同样的规律。     

乙烯-四氟乙烯共聚物非等温结晶行为

采用差示扫描量热仪(DSC)和偏光显微镜(PLM)对乙烯-四氟乙烯共聚物(ETFE)的非等温结晶行为进行了研究,并用莫志深法和Kissinger法对结晶动力学进行处理。结果表明,随着降温速率增大,ETFE的结晶温度逐渐下降,结晶温度范围变宽;ETFE的结晶过程分三阶段进行,分别为成核阶段、由晶核生成球晶阶段和球晶碰撞并生长阶段;ETFE的非等温结晶活化能随着共聚物中C2F4组分的增加而增加。     

Strain-induced crystallization behavior of poly(ether ether ketone) (PEEK)

Strain-induced crystallization of poly(ether ether ketone) (PEEK) was studied by the use of a parallel plate rheometer. The experimental variables included preheating time, crystallization temperature, and shear rate. The crystallization kinetics were characterized by means of an induction time defined as the time elapsed from the start of shearing to the onset of crystallization. The experimental results showed that the induction time for strain-induced crystallization of PEEK was significantly shorter than that for crystallization under quiescent condition, and that strain-induced crystallization was much less temperature dependent than quiescent crystallization. The activation energy for strain-induced crystallization was found to be 0.035kcal/mole, which was considerably smaller than the reported activation energy for quiescent crystallization. Photomicrographs of the sheared specimens indicated that PEEK crystallites orient along the flow direction.     

玻纤增强PC/PBT合金的结晶行为

研究了在玻纤增强的聚碳酸酯(PC)/聚对苯二甲酸丁二酯(PBT)合金中PBT的结晶行为。发现PBT的结晶过程是由两种相反的影响共同决定的,一方面玻纤能够诱导PBT成核,加快PBT的结晶速率;另一方面,PC会抑制PBT结晶,降低PBT的结晶速率。同时发现在不同组成比下,PC/PBT合金会形成不同的相形貌,也会影响玻纤对PBT结晶的成核作用和PC对PBT结晶的抑制作用,进而使PBT呈现加速结晶、分级结晶或者受限结晶行为。基于以上结果,提出了玻纤增强PC/PBT合金中PBT的结晶机理。同时考察了PC/PBT合金的结晶行为和热性能之间的关系。     

溶析结晶法分离莱鲍迪甙A的工艺研究

采用溶析结晶法分离甜菊糖苷中的莱鲍迪甙A(RA),考察溶析剂及其含量、溶液浓度、结晶温度、结晶时间对结晶率和分离系数〔0.87×SRA/(Stotal-SRA)〕的影响。结果表明,在乙酸乙酯含量50%,溶液浓度20 g/L,结晶温度18℃,结晶时间8 h的条件下,结晶率为0.34,分离系数为3.8。     

生物基尼龙56的等温结晶性能研究

采用差示扫描量热仪和带有热台的偏光显微镜对生物基尼龙56的等温结晶性能进行了研究。用Avrami方程对等温结晶过程及其动力学进行了分析,得出Avrami指数(n值)在2.30~3.37之间,推测其晶体生长方式为三维球状生长;采用Arrhenius方程计算了生物基尼龙56的等温结晶活化能(ΔE)为-99.04 kJ/mol。偏光显微镜研究证实了上述推测,同时发现球晶半径与结晶时间呈线性关系,求得了球晶的生长速率。     

四苯基氯化鏻对聚偏氟乙烯电活性相的诱导作用

通过简单的熔体共混方法,将不同质量分数的高熔点高活性的四苯基氯化鏻(TPPC)与聚偏氟乙烯(PVDF)混合,探究了TPPC对PVDF极性相的诱导作用,并研究了此体系与熔体结晶过程最为相近的非等温结晶过程。结果表明,添加极少量(0.4%)的TPPC即可以使PVDF直接从熔体中全部以极性相结晶,这归因于TPPC固体表面的电荷与PVDF分子链之间强烈的相互作用。TPPC的加入使PVDF的非等温结晶行为发生了很大的变化,当TPPC含量达到0.4%时,降温结晶曲线出现两个结晶峰,也是这种反常的结晶行为才能使PVDF几乎全部以极性相结晶。     

Isothermal crystallization kinetics of in situ Nylon 6/graphene composites by differential scanning calorimetry

The isothermal crystallization kinetics of nylon 6/graphene (NG) composites prepared by in situ polymerization was investigated by differential scanning calorimetry. The Avrami equation was used to study the crystallization kinetics. Comparing with nylon 6, it is found that the NG composites (NG‐0.1, NG‐0.5, and NG‐1.0, where the number describes the wt% content of graphene) had higher crystallization rates; the crystallization rate increased remarkably with 0.1 wt% graphene. However, too many crystallization nuclei could not accelerate the crystallization process effectively. The t_max values obtained from the plots of heat flow versus time were in agreement with the t_max values calculated from the half time of crystallization when the graphene content was lower than 1.0 wt%, which means that the values of the Avrami parameters calculated from the half time of crystallization might be in better agreement with the actual crystallization mechanism than that determined from the Avrami plots. The n values of the NG composites ranged between 1.1 and 1.8, which can be interpreted as meaning both one‐dimensional and two‐dimensional crystallization growth occurred during isothermal crystallization process. The activation energies, which were determined by the Arrhenius' method, varied within the range from ?188 to ?142 kJ/mol. POLYM. ENG. SCI., 54:2610–2616, 2014. © 2013 Society of Plastics Engineers     

Crystallization of isotactic polystyrene induced by organic vapours

The crystallization of isotactic polystyrene induced by dichloromethane and acetone was studied. From equilibrium absorption data, the critical concentration for crystallization was deduced. The crystallization kinetics were followed and diffusion coefficients were calculated. It was found that the crystallization was diffusion controlled. The increase in the rate of crystallization is explained by the high rate of diffusion and nucleation in the presence of the organic solvents. Evidence for the high nucleation probability was found in morphological observations (SAXS and electron microscope observations). The melting behaviour of the solvent crystallized samples suggests formation of a very unstable crystalline structure which re-organizes rapidly on heating.     

Surface Properties – A Key for Nucleation in Melt Crystallization Processes

Numerous organic products which are commercially refined by crystallization exhibit wide metastable zones, for example, xylene, bisphenol‐A, isocyanates, or pyridine derivatives. The practical meaning for layer crystallization processes is that a high degree of subcooling on crystallization surfaces is necessary to start nucleation at the beginning of a crystallization stage. The subsequent crystallization runs then uncontrolled, at much higher rates than designed until the subcooling has been dissipated. As a consequence dendritic crystal growth sets in, which is disadvantageous in terms of the separation efficiency of the crystallization process. A practicable countermeasure is seeding which, however, requires more complex equipment and generates additional process steps, resulting in additional costs. In this work an alternative way of reducing the negative impact of subcooling on crystallization, which is based on the reduction of the metastable zone itself rather than on the bypassing it, has been investigated. The width of the metastable zone depends on the activation energy for nucleation which in turn depends on the interfacial surface tension between the melt and the surface of the crystallization element. It has been shown in this work that the activation energy for nucleation and so the supercooling in a xylene isomer mixture can be considerably reduced when replacing stainless steel by PTFE as a material for the crystallization surface. In follow‐up trials it was found that the crystallization surfaces do not need to be wholly covered by PTFE but that just small PTFE nucleation zones on steel surfaces have the same positive effect on the separation by crystallization. Applied in industrial equipment such nucleation zones might contribute to the cost optimization of commercial layer crystallization processes.     

湿度对单轴取向PET纤维结晶过程的影响

采用DSC研究了不同拉伸比的单轴取向PET纤维在不同湿度下的冷结晶过程。发现湿度可以诱导纤维双重结晶峰的出现。从DSC图可以看出,随着湿度的提高,结晶峰向低温移动,且分化成两个较小的结晶峰,结晶可在玻璃化转变温度之下发生。DSC数据处理结果表明,所得Avrami指数呈规律变化,由于湿度的影响,单轴取向PET纤维在低温时的结晶机理发生变化。