聚甲醛成核剂对其结构和性能的影响研究

利用偏光显微镜、差示扫描量热仪和力学性能测试机研究了成核剂氮化硼(BN)、纳米碳酸钙和碳酸钙对聚甲醛的结构和性能的影响。结果显示,3种成核剂均能有效地减小聚甲醛晶粒尺寸,BN使POM的结晶峰温度和结晶起始温度提高,而纳米碳酸钙和碳酸钙却使其降低。力学测试表明,3种成核剂能使POM缺口冲击能力较大幅度地提高,拉伸强度略微下降。     

改性聚甲醛结晶性能研究

采用差示扫描量热仪和偏光显微镜,对未加成核剂和加入2种不同成核剂A、B的聚甲醛（POM）进行非等温结晶测试、等温结晶动力学研究,得到了在各种条件下的Avrami方程参数(K和n)、半结晶时间(t1/2)及结晶形态。研究表明,POM结晶过程为异相三维生长过程,2种成核剂均能使POM结晶速度加快,缩短了结晶时间,成核剂B效果好于成核剂A。     

复合成核剂HCA-1对PBT结晶性能的影响

采用差示扫描量热仪(DSC)研究了复合成核剂HCA-1对聚对苯二甲酸丁二醇酯(PBT)结晶性能的影响.对所得数据用修正Avrami方程的Jeziorny法进行处理.结果表明:复合成核剂HCA-1的加入使得PBT的结晶温度、结晶速率得到显著提高;尤其是在高降温速率下,PBT的结晶温度提高20℃以上,显示了复合成核剂HCA-1对PBT结晶性能的良好促进作用.     

聚甲醛结晶成核剂研究进展

对国内外聚甲醛(POM)结晶成核剂进行了分类。概述了碳酸钙、滑石粉、硅藻土等无机成核剂,碳纳米管、聚酰胺、均聚甲醛等有机成核剂,氧化镁、超细Fe粉等金属类成核剂及滑石粉/弹性体等复合成核剂对POM结晶性能和力学性能等的影响。对POM成核剂的开发提出了建议。     

成核剂对共聚甲醛MC90结晶与力学性能的影响

利用差示扫描量热仪、偏光显微镜和万能材料试验机等研究了不同成核剂用量对聚甲醛MC90的结晶行为和力学性能的影响。结果表明,成核剂的加入可有效减小POM的球晶尺寸,提高POM的结晶温度和缺口冲击强度。当成核剂添加量为0.8%时,最大结晶温度由139.2℃提高到143.3℃,球晶平均尺寸约60μm,为未加成核剂的POM球晶尺寸的1/2,缺口冲击强度由5.5k J·m~(-2)增加到6.1k J·m~(-2)。     

成核剂对聚羟基丁酸己酸酯结晶性能的影响

采用溶液浇铸法制备了含不同成核剂的生物可降解聚羟基丁酸己酸酯(PHBHHx)样品,利用热台偏光显微镜(POM)和差示扫描量热(DSC)法研究了成核剂对PHBHHx结晶行为和热性能的影响,并对比了氮化硼、羟基磷灰石和木质素磺酸钠三种成核剂的效果.结果表明,加入成核剂后,PHBHHx的结晶发生异相成核,球晶数目增加,从POM的结果看,木质素磺酸钠的成核效果最好.PHBHHx的结晶诱导期大大缩短,含木质素磺酸钠的PHBHHx的效果尤其明显.等温结晶和非等温结晶的DSC分析表明,羟基磷灰石促进结晶的能力最强.     

成核剂对聚甲醛结构与性能的影响

本文通过加入少量成核剂氮化硼于聚甲醛中,使其生成小而均匀的球晶,从而提高了力学性能和尺寸稳定性。     

聚甲醛成核剂研究进展

综述了硅藻土、硅胶、蒙脱土、滑石粉和氮化硼等无机成核剂,聚酰胺、羧酸盐等有机成核剂对聚甲醛(POM)结晶性能和力学性能的影响。由弹性体和滑石粉组成的复合成核剂不仅可使POM的球晶尺寸减小至2.1μm,更重要的是使POM的成型收缩率从3.3%降至2.0%。开发POM成核剂一是要根据POM的结构特征,通过分子设计,合成适合POM专用的系列成核剂;二是通过对现有成核剂的物理或化学复合,开发复合成核剂,发挥不同组分的协同效应。     

成核剂对PET/PEN共混体系非等温结晶的影响

采用差示扫描量热法(DSC)研究了三种成核剂苯甲酸钠(SB)、1,3∶2,4-二亚苄基-D-山梨醇(DBS)、碳酸钙(CaCO3)对聚对苯二甲酸乙二醇酯(PET)/聚2,6-萘二甲酸乙二醇酯(PEN)共混体系的非等温结晶动力学的影响。结果表明,在PET/PEN/成核剂共混体系的非等温熔融结晶过程中,随着冷却速率的升高,结晶起始温度、终止温度、结晶峰温度都向低温方向移动,成核剂的加入使得不同速率下PET/PEN的结晶温度明显提高,结晶更为容易,SB、CaCO3、DBS均起到了较好的成核作用。由于次级结晶的存在,采用Ozawa法不能很好地描述PET/PEN/成核剂共混体系的非等温熔融结晶过程;莫志深法能较好地描述体系的非等温熔融结晶过程。     

成核剂A对聚甲醛结构与性能的影响

本文利用差热分析仪、偏光显微镜、广角Ｘ射线衍射仪及力学性能测试设备考察了成核剂Ａ对聚甲醛结构与性能的影响．研究发现，成核剂Ａ的加入，使得聚甲醛球晶细化，结晶速度加快，结晶过程为异相成核三维生长过程；且不改变ＰＯＭ的结晶晶型．但结晶度下降，微晶尺寸增大；含有成核剂Ａ的ＰＯＭ具有较高的缺口冲击强应，使得ＰＯＭ的缺口敏感性下降，因而可扩大ＰＯＭ的应用领域．     

Nonisothermal crystallization kinetics of polyoxymethylene/montmorillonite nanocomposite

The nonisothermal crystallization kinetics of polyoxymethylene (POM), polyoxymethylene/Na–montmorillonite (POM/Na–MMT), and polyoxymethylene/organic–montmorillonite (POM/organ–MMT) nanocomposites were investigated by differential scanning calorimetry at various cooling rates. The Avrami analysis modified by Jeziorny and a method developed by Mo were employed to describe the nonisothermal crystallization process of POM/Na–MMT and POM/organ–MMT nanocomposites. The difference in the values of the exponent n between POM and POM/montmorillonite nanocomposites suggests that the nonisothermal crystallization of POM/Na–MMT and POM/organ–MMT nanocomposites corresponds to a tridimensional growth with heterogeneous nucleation. The values of half‐time and the parameter Z_c, which characterizes the kinetics of nonisothermal crystallization, show that the crystallization rate of either POM/Na–MMT or POM/organ–MMT nanocomposite is faster than that of virgin POM at a given cooling rate. The activation energies were evaluated by the Kissinger method and were 387.0, 330.3, and 328.6 kJ/mol for the nonisothermal crystallization of POM, POM/Na–MMT nanocomposite, and POM/organ–MMT nanocomposite, respectively. POM/montmorillonite nanocomposite can be as easily fabricated as the original polyoxymethylene, considering that the addition of montmorillonite, either Na–montmorillonite or organ–montmorillonite, may accelerate the overall nonisothermal crystallization process. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2281–2289, 2001     

热经时处理对聚甲醛结晶行为的影响

考察了热经时处理对聚甲醛（POM）结晶行为的影响。结果表明,纯POM结晶是一个成核控制的过程．随着热处理温度的提高或热处理时间的延长,POM的晶核数目明显减少,球晶尺寸和半结晶时间t1/2显著增大,且与片晶相关的球晶显微结构上的有序性也将发生不可逆转的下降;而热稳定剂对POM的结晶产生抑制作用,并通过阻止和延缓POM的热分解对POM结晶速率变慢起到稳定的作用,但这两种作用在某种程度上是相互制约的．随着热处理时间的延长,两种作用将达到平衡;POM的分子量越小,半结晶时间t1/2增加的速度越大,但无论POM分子量大或小,其热处理条件下的结晶行为如晶核数目、球晶尺寸、半结晶时间t1/2等变化规律都反映出与纯POM相同的倾向。     

Crystallization characteristics of polyoxymethylene with attapulgite as nucleating agent

The nucleation of polyoxymethylene (POM) crystallization using attapulgite was studied using differential scanning calorimetry, polarized light microscopy, wideangle X‐ray diffration and mechanical testing. Two isothermal crystallization kinetic equations were employed to describe the crystallization of virgin POM and POM containing attapulgite as a nucleating agent. The addition of attapulgite decreased the spherulitic size of POM, and interfacial free energies per unit area perpendicular to the molecular chain direction ρ_e, accelerated the crystallization growth rate and enhanced the impact toughness of POM, but no change occurred for the hexagonal system of POM. The addition of attapulgite up to its saturation concentration in POM increased the number of effective nuclei by three orders of magnitude. A high concentration of attapulgite caused agglomeration of the agent and lowered the number of effective nuclei.     

聚甲醛结晶性能的改性

研究了高摩尔质量羧酸盐类成核剂HC对聚甲醛（POM）的结晶成核作用，采用示差扫描量热分析（DSC）、偏光显微镜观察（PLM）及等温结晶动力学分析等方法研究了该类成核剂对POM结晶形态、结晶度、结晶速率等的影响，并考察了其力学性能。结果表明，高摩尔质量羧酸盐类成核剂HC的加入，使POM晶粒细化，结晶诱导期缩短，显著提高了POM的结晶速率。     

聚甲醛及其纤维的热分析研究

用Ozawa法和Mo法对聚甲醛(POM)的非等温结晶动力学进行研究。采用双螺杆纺丝机熔融纺得POM初生纤维,再用水浴拉伸方法制得POM纤维,研究拉伸倍数、水浴温度对POM纤维结晶性能的影响。结果表明:在不同的降温速率下,随着降温速率的提高,POM结晶峰峰值温度降低,半结晶时间缩短,结晶速率加快;采用Mo法研究POM的非等温结晶过程比较理想,而Ozawa法不适用;水浴拉伸有利于纤维的结晶,而随着水浴温度的提高,POM纤维的结晶度提高。     

Isothermal crystallization behavior of polyoxymethylene with and without nucleating agents

Nucleation effects of two silicate nucleating agents, attapulgite and diatomite, on the crystallization of polyoxymethylene (POM), were studied by means of differential scanning calorimetry and polarized optical microscopy. The crystallization kinetics of POM with and without nucleating agents was analyzed by means of two isothermal crystallization kinetic equations through the crystallization thermograms. Compared with virgin POM, POM with nucleating agents of attapulgite and diatomite decreased the spherulitic size of POM and interfacial free energies per unit area perpendicular σ_e. The crystallization growth rate was accelerated because of nucleating agents as well. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 304–310, 2001     

POM与POM/碳酸钙复合材料非等温结晶动力学研究

采用差示扫描量热仪研究了聚甲醛（POM）和POM /碳酸钙复合材料在不同降温速率下的非等温结晶行为,并用Jeziorny法和莫志深法计算了POM及其复合材料的非等温结晶动力学参数。结果表明：提高降温速率,POM与POM/碳酸钙复合材料的结晶峰均向低温方向移动,且结晶放热峰逐渐变宽;降温速率为5、10、15和20 ℃/min时对应POM/碳酸钙复合材料的结晶峰峰值和结晶放热焓分别为144.6、142.4、141.2、140.2 ℃和177.4、152.2、148.0、137.2 J/g;加入碳酸钙的使POM的结晶温度提高,结晶速率加快,其在体系中起到了异相成核的作用。     

PE-UHMW对聚甲醛力学性能及非等温结晶的影响研究

制备了一系列聚甲醛/超高相对分子质量聚乙烯（POM/PE-UHMW）共混物,并通过力学性能测试,差示扫描量热仪及扫描电子显微镜等分析了共混物的结构和性能,分别采用Avrami以及莫志深理论对POM及POM/PE-UHMW(100/1)非等温结晶动力学进行了理论分析,利用Kissinger方法对其结晶活化能进行了计算。结果表明,当PE-UHMW含量为1 %(质量分数,下同)时,共混物的缺口冲击强度达到最大值,较纯POM提高了约24.3 %;同时其降低了POM的结晶速率和结晶活化能,但相对结晶度稍有提高。     

POM /TPU共混物非等温结晶动力学研究

采用差示扫描量热法(DSC}研究了不同冷却速率下聚甲醛( POM)以及POM/热塑性聚氨酷弹性体(TPU)共混物的非等温结晶过程,分别采用Jeziorny法、Ozawa法和Mo法进行处理。结果表明:随着冷却速率的增大,POM及其共混物的结晶峰都变宽,结晶峰值温度(Tc)都降低;在相同冷却速率下,POM /TPU共混物的Tc。较纯POM有所提高;Jeziorny法和Mo法处理非等温结晶过程比较理想,而由于次级结晶的存在Ozawa法并不适用;Jeziorny法和Mo法处理所得的数据表明,TPU的加人能够提高POM的结晶速率,减小半结晶时间(t1/2),并且导致POM的结晶成核和生长发生了改变。     

High Efficiency Nucleating Agents of Polyoxymethylene

In this research, the effects of different kinds of nucleating agents on the crystallization and mechanical properties of polyoxymethylene (POM) were studied, including inorganic, organic, and polymer nucleating agents and their compounds. These properties showed that nanoCaCO₃, sorbitol derivative TMB-5, polyamide PA-4, and compound C-1/polyamide (PA)-4 can make spherulites of POM finer and more perfect, and effectively improve its notched impact toughness, in which the compound C-1/PA-4 displayed more remarkable nucleation effect. The study on the nonisothermal crystallization of POM showed that the crystallization temperature and crystallization growth rate of POM increased when C-1/PA-4 was added. The isothermal crystallization kinetics were also analyzed by the Avrami equation. The addition of C-1/PA-4 can increase the values of the Avrami exponent (n) and crystallization rate constant (k), and reduce the half-time of isothermal crystallization, t_1/2, and the time corresponding to the maximum rate of crystallization, t_P, indicating its remarkable nucleating effect on POM.