在低频振动场中注塑成型iPP试样的结构与性能研究

利用自行研制的低频振动注塑成型装置进行等规聚丙烯(iPP)试样的结构与性能研究.实验中对常规注射和振动注射成型的试样力学性能和微观形态进行了对比实验.采用低频振动注塑成型工艺实现了IPP试样的自增强,在190℃下进行注射,强度由常规试样的41.3 MPa最大提高到振动试样的48.4 MPa(振幅PA=59.4 MPa,振频FR=0.7 Hz),强度提高了17.2%;SEM显示常规试样芯层结构主要由球晶构成,振动注射使球晶在流动方向上变形、取向,晶粒尺寸得到细化;DSC表明振动注射促进熔融峰向高温漂移,晶体结晶更加完善,结晶度最大提高了12.1%;WAXD显示低频大振幅振动注塑有利于γ晶型的生成,γ晶型有利于试样实现自增强.     

聚丙烯催化合金(PP-c)的晶体结构及其影响因素

用差示扫描量热法(DSC)和广角X射线衍射(WAXD)研究了两种乙烯含量不同的聚丙烯反应合金(PP-c)等温结晶下的晶体结构及PPβ晶含量的影响因素.结果表明,在通常的等温结晶条件下,乙烯含量较高的试样(PEP40)的熔融曲线出现双熔融峰.WAXD分析证明,其熔融双峰分别代表均聚聚丙烯(PP)的α晶和β晶.计算结果表明,PEP40中β晶含量与结晶温度有关,124℃结晶时β晶含量最高.在220℃对PP-c熔体进行热处理可显著提高PEP40中β晶的含量;在相同温度下热处理后,较低乙烯含量的试样(PEP20)也出现晶型异构.比较200℃与220℃下热处理对PEP20等温结晶的结晶形态的影响,发现后者使微晶尺寸明显变小,并呈现较完善的β球晶形态.     

聚丙烯/累托石纳米复合材料的非等温结晶动力学研究

在双螺杆挤出机上熔融共混制备了聚丙烯 (PP) 有机累托石 (OREC)纳米复合材料 ,采用广角X 射线衍射 (WAXD)定性地分析了PP OREC纳米复合材料及纯PP的结晶形态 ,由半峰宽定性地判断了对应晶面法向的晶粒的大小 .结果表明有机累托石没有改变聚丙烯的结晶晶型 (纳米复合材料主要还是α晶型 ) ,但是细化了晶粒的尺寸 .采用差示扫描量热法 (DSC)定量地研究了复合材料的非等温熔融结晶动力学 ,对所得数据分别用Jeziorny法的Mo法进行了处理 ,表明非等温结晶动力学参数Zc 及Avrami指数n随冷却速率的增加而增加 ,复合材料的Avrami指数n大于纯PP的n ;对相同配比的纳米复合材料 ,随着结晶度的增加 ,单位结晶时间里达到一定结晶度所需要的降温速率F(T)增大 ,对同一个设定的结晶度 ,纳米复合材料的F(T)比纯PP的小 ,说明需要的降温速率减小 .所有这些均说明有机累托石可作为聚丙烯的结晶成核剂 .     

多熔体多次注塑成型沿流动方向上微观结构演变探究

不同于传统注射成型,多熔体多次注塑成型(M³IM)过程中存在特殊的二次流动场和温度场,导致其试样的形态结构与演变规律更加复杂.本文采用实验与模拟相结合的方法,详细探究了熔体沿流动方向上二次流动过程中剪切场和温度场的分布,及其对试样形态结构的影响.结果发现,一次注射聚偏氟乙烯(PVDF)熔体是由一次流动层和二次流动层两部分所构成,且在一次流动层末端形成熔体突破区.此外,剪切场和温度场在熔体突破区前段、中段和后段存在显著差异,导致试样微观结构沿流动方向呈多级分布,即在突破区前段PVDF形成取向结构,而在突破区段PVDF受到强的二次剪切作用,形成了大量β晶和取向结构.与此不同,在突破区后段,PVDF则主要受到二次剪切生热作用的影响,形成了具有较高熔点(～190℃)的特殊“亮带”结构.     

长链支化聚丙烯结晶行为及发泡性能研究

通过广角X射线衍射(WAXD)、示差扫描量热(DSC)和偏光显微镜(POM)研究了长链支化聚丙烯(LCBPP)和线性等规聚丙烯(PP)的结晶行为.WAXD和DSC的结果显示LCBPP样品有利于β结晶,出现了少量β晶.DSC和POM的结果显示在等温结晶过程中长链支化结构起到促进异相成核和细化晶粒的作用,LCBPP样品的结晶温度提高,结晶速度增大,球晶尺寸显著减小.采用间歇釜式超临界二氧化碳发泡法对LCBPP和线性PP样品进行发泡,由于LCBPP结晶温度高,结晶速率更快,有利于泡孔的固化定型,可以提高发泡温度,研究结果表明在相同的发泡压力下LCBPP样品发泡温度窗口较宽,为5 K左右,而线性PP样品的发泡温度窗口较窄,仅为2 K左右,同时在相同的发泡条件下LCBPP样品的发泡倍率较大.     

丙烯酸及其接枝物对纳米CaCO3/PP结晶与熔融行为的影响

制备了丙烯酸(AA)及其接枝聚丙烯(PP—g-AA)改性的纳米CaC03／PP复合材料。用DSC研究了纳米CaCO3对PP、PP-g-A和AA对纳米CaCO3／PP中PP结晶与熔融行为的影响。结果表明：随纳米CaCO3用量增加，PP结晶与熔融温度提高，PP—g—AA加入使PP结晶温度进一步提高，PP的结晶温度也随从用量增加而提高；在过氧化二异丙苯(DCP)存在下，少量AA能明显提高PP的结晶温度，但增加从用量对结晶温度的影响较小；WAXD证实纳米CaCO3／PP复合材料中存在β晶。     

多组分单体接枝聚丙烯/尼龙6反应共混物结晶行为研究

用多组分熔融接枝的方法将甲基丙烯酸缩水甘油酯 (GMA)和苯乙烯 (St)共同接枝到聚丙烯 (PP)上 ,制得具有较高GMA接枝率的多单体接枝聚丙烯 ,PP g (GMA co St) .将PP g (GMA co St)与尼龙 6 (PA6 )进行共混 ,利用扫描电镜 (SEM) ,差示扫描量热计 (DSC)和广角X射线衍射 (WAXD)对共混物的形态和结晶进行了研究 .在共混过程中 ,PP g (GMA co St)与PA6反应原位生成了PP g PA6 ,有效改善了共混物的相容性 ,分散相尺寸明显减小 .在PP g (GMA co St) PA6为 3 7的体系中 ,PP g (GMA co St)出现分级结晶现象 ,其在较低温度下的结晶属于均相成核结晶 .在PP g (GMA co St) PA6为 7 3的体系中 ,由于PA6相分散细微 ,在通常结晶温度下不结晶 ,而是在低温下均相成核与PP g (GMA co St)同时结晶 .WAXD证实体系中接枝PP ,PA6为分别结晶 ,无共晶或新的晶型产生     

纳米碳酸钙/庚二酸复合成核剂对热致相分离法制备聚丙烯微孔膜的影响

以大豆油/邻苯二甲酸二丁酯(DBP)为混合稀释剂,采用热致相分离法(TIPS)制备聚丙烯(PP)微孔膜.研究了纳米碳酸钙成核剂、纳米碳酸钙/庚二酸复合成核剂对PP/大豆油/DBP(30/42/28,质量比)混合体系中PP结晶、熔融性能和PP微孔膜微观结构的影响.结果表明,单一纳米碳酸钙成核剂加入量为PP的0%~4%(质量百分率)时,PP/DBP/大豆油体系中PP熔融曲线上对应的峰值温度(Tpm)降到150.7~151.3℃,而纯PP的熔融峰值温度为165℃;DSC实验结果还显示加入1%~4%纳米碳酸钙和0.5%庚二酸后,导致PP的熔融曲线上出现了熔融双峰,说明纳米碳酸钙/庚二酸复合成核剂与单一成核剂相比有明显地促进β晶生成的作用,宽角X射线衍射(WAXD)实验进一步证实了β晶的存在.单一纳米碳酸钙成核剂对PP微孔膜的球晶结构和微观孔结构影响不大;加入纳米碳酸钙/庚二酸复合成核剂明显影响PP微孔膜的球晶结构和微观孔结构,其中0.5%庚二酸和1%纳米碳酸钙组成的复合成核剂制得的PP微孔膜的球晶结构明显,微孔膜孔径小且分布均匀;进一步增加纳米碳酸钙用量,PP微孔膜生成了许多细小的边界模糊的不规则结晶,微孔膜孔径不规则且尺寸较大,这与此时PP形成β晶结构有关.     

硅氧烷液晶共聚物作为β晶成核剂对等规聚丙烯结晶结构与形态的影响

采用广角X射线衍射(WAXD)与偏光显微镜(POM)等手段研究了硅氧烷液晶共聚物(LCP-O2)作为新型成核剂对聚丙烯(PP)共混样品结晶结构与形态的影响.结果表明,低浓度的LCP-O2在PP共混体系中起到异相成核的作用,使PP的晶核数目增多,球晶细化,并提高了结晶速度,同时也诱导出了β晶的形成.LCP-O2的成核效果主要依赖于其在PP中的相对含量、液晶的分子结构与结晶的热处理过程,且随着结晶温度或成核剂含量的增加,对应PP试样的β晶含量(Kβ)呈现先增加,后降低的趋势.当LCP-O2质量分数为1.0%,在130℃等温结晶1h,对应PP试样的Kβ最大,为58%.此外,属于单斜晶的α球晶呈现黑白颜色,晶束呈放射状生长,边界清晰;而属于三方晶的β球晶亮度要高于α球晶,其颜色艳丽多彩,束状晶片聚集体呈支化生长,内部排列比α晶疏散,边界相对模糊,且β晶与α晶的形态分别在157和171℃完全消失.     

PP-g-MAEu离聚物的合成与表征

以过氧化二异丙苯(DCPO)为引发剂,将马来酸铕(MAEu)熔融接枝到聚丙烯上,合成不同接枝率的PP-g-MAEu离聚物,考察了反应时间、引发剂浓度、单体用量对接枝率的影响,在离聚物的1540～1643 cm-1之间的宽峰说明MAEu与PP发生了接枝反应;利用WAXD, POM和DSC考察了PP及其接枝物的结晶行为, PP-g-MAEu能促进β-型结晶的形成,接枝物的起始结晶温度移向高温,结晶速率加快,接枝物形成的球晶尺寸变小,而且球晶不规整;荧光光谱的结果表明PP-g-MAEu离聚物是一种单色性好、亮度高的稀土高分子光致发光材料.     

Multiple Melting Endotherms of Syndiotactic Polystyrene in β Crystalline Form

Multiple melting behaviors have been studied extensively. Syndiotactic polyStyrene(SPS), in 6 crystalline form exhibited such phenomena. It was suggested that arecrystallization process occurred since it has been clarified that no other modificationswere observed during the DSC heating scanl. In this study, a series of SPS samples in 0form were prepared by cooling from the melt at various cooling ratesl and the factors thatinfluence the multiple melting behavior of SPS in 0 form were exam…     

Effect of temperature on dynamic rheological behavior of discontinuous cubic liquid crystal

The dynamic rheological properties of discontinuous cubic liquid crystal, formed by nonionic surfactant C(12-14)E(12), were investigated in the discrete and continuous patterns of raising temperature. In the discrete pattern, the discontinuous cubic phase appears in two types of viscoelastic behaviors under the melting points of cubic phase: elastic gel and viscoelastic liquid. When the discontinuous cubic phase begins to melt, it has the weak polymer-like viscoelasticity. Temperature and shear frequency have completely different effects on the ratio of viscous and elastic components of samples in these three states. At low temperature, the samples dominate in elasticity and temperature and shear frequency has hardly any effect on viscoelasticity. At moderate temperature, its ratio of viscous and elastic components increases with increasing temperature and decreasing shear frequency. At the vicinity of the melting point of cubic liquid crystal, the cubic liquid crystal appears to have almost equaled viscous and elastic component; shear has obvious effect on the ratio of viscoelasticity at low frequency. The results from the continuous pattern of raising temperature are consistent with those from the discrete pattern.     

Crystallization and melting of isotactic polypropylene in response to temperature modulation

Isotactic polypropylene (iPP) was crystallized using temperature modulation in a differential scanning calorimeter (DSC) to thicken the crystals formed on cooling from the melt. A cool-heat modulation method was adopted for the preparation of the samples under a series of conditions. The effect of modulation parameters, such as temperature amplitude and period was monitored with the heating rate that followed. Thickening of the lamellae as a result of the crystallization treatment enabled by the cool-heat method lead to an increase in the peak melting temperature and the final traces of melting. For instance, iPP melting peak shifted by up to 3.5°C with temperature amplitude of 1.0°C while the crystallinity was increased from 0.45 (linearly cooled) to 0.53. Multiple melting endotherms were also observed in some cases, but this was sensitive to the temperature changes experienced on cooling. Even with a slower underlying cooling rate and small temperature amplitudes, some recrystallization and reorganization occurred during the subsequent heating scan. The crystallinity was increased significantly and this was attributed to the crystal perfection that occurred at the crystal growth surface. In addition, temperature modulated differential scanning calorimetry (TMDSC) has been used to study the melting of iPP for various crystallization treatments. The reversing and non-reversing contribution under the experimental time scale was modified by the relative crystal stability formed during crystallization. Much of the melting of iPP was found to be irreversible.This revised version was published online in November 2005 with corrections to the Cover Date.     

Preferential formation of electroactive crystalline phases in poly(vinylidene fluoride)/organically modified silicate nanocomposites

The role of organically modified silicate (OMS), Lucentite STN on the formation of β‐crystalline phase of poly(vinylidene fluoride) (PVDF) is investigated in the present study. The OMS was solution blended with PVDF and cast on glass slide to form PVDF‐OMS nanocomposites. Solution cast samples were subjected to various thermal treatments including annealing (AC‐AN), melt‐quenching followed by annealing (MQ‐AN), and melt‐slow cooling (MSC). Fourier‐transform infrared spectroscopy (FT‐IR), wide angle X‐ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the crystalline structure of thermally treated samples. As a special effort, the combination of in situ thermal FT‐IR, WAXD, and DSC studies was utilized to clearly assess the thermal properties. FT‐IR and WAXD results of MQ‐AN samples revealed the presence of β‐phase of PVDF. Ion‐dipole interaction between the exfoliated clay nanolayers and PVDF was considered as a main factor for the formation of β‐phase. Melt‐crystallization temperature and subsequent melting point were enhanced by the addition of OMS. Solid β‐ to γ‐crystal phase transition was observed from in situ FT‐IR and WAXD curves when the representative MQ‐AN sample was subjected to thermal scanning. Upon heating, β‐phase was found to disappear through transformation to the thermodynamically stable γ‐phase rather than melting directly. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2173–2187, 2008     

Analysis of Polymorphism and Dual Crystalline Morphologies in Poly(hexamethylene terephthalate)

Summary: The polymorphisms in poly(hexamethylene terephthalate) (PHT), along with their associated melting and spherulite morphologies, were examined by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and polarized‐light microscopy (PLM). The morphology and crystal cells were dependent on the temperature of crystallization. When melt‐crystallized at low temperatures (90–135 °C), PHT showed at least five melting peaks and two re‐crystallization peaks upon DSC scanning, and the samples displayed various fractions of both α and β crystals. However, only a single melting peak was obtained in PHT melt‐crystallized at 140 °C or above, which displayed a single type of β crystal. In addition, two different forms of spherulites were identified in melt‐crystallized PHT, with one being a typical Maltese‐cross spherulite containing the α crystal, and the other being a dendrite‐type packed mainly with the β crystal. This study provides timely evidence for a critical interpretation of the relationship between multiple melting and polymorphisms (unit cells and spherulites) in polymers, including semi‐crystalline polyesters.

WAXD diffractograms for PHT melt‐crystallized at 140 °C, revealing a single type of β‐crystal cell.     

Real-time X-ray scattering study during heating of oriented injection-molded polyethylene

Highly oriented linear polyethylene was prepared by elongational flow injection molding. The changes in crystal orientation were investigated as a function of temperature by real-time wide-angle X-ray diffraction. Additionally, the influence of molecular weight upon the microstructure and the changes in orientation, during heating near the melting point, and after cooling have been examined. A shish-kebab structure is inferred for the high molecular weight samples (M_w≥10⁵) from SAXS observations, while for samples with M_w<10⁵ only an oriented lamellar structure is found. Consequently, a higher thermal stability is shown by the higher molecular weight samples. Furthermore, a recovery of crystal orientation on rapid cooling of the samples from the melt is only observed for samples with M_w≥10⁵. The results are discussed in terms of a preferential recrystallization of chain-folded lamellae, on cooling, onto the shish fibrils which survive at high temperature.     

X‐ray studies on the double melting behavior of poly(butylene terephthalate)

The double melting behavior of poly(butylene terephthalate) (PBT) was studied with differential scanning calorimetry (DSC) and wide‐angle X‐ray analysis. DSC melting curves of melt‐crystallized PBT samples, which we prepared by cooling from the melt (250 °C) at various cooling rates, showed two endothermic peaks and an exothermic peak located between these melting peaks. The cooling rate effect on these peaks was investigated. The melt‐crystallized PBT sample cooled at 24 K min^?1 was heated at a rate of 1 K min^?1, and its diffraction patterns were obtained successively at a rate of one pattern per minute with an X‐ray measurement system equipped with a position‐sensitive proportional counter. The diffraction pattern did not change in the melting process, except for the change in its peak height. This suggests that the double melting behavior does not originate from a change in the crystal structure. The temperature dependence of the diffraction intensity was obtained from the diffraction patterns. With increasing temperature, the intensity decreased gradually in the low‐temperature region and then increased distinctly before a steep decrease due to the final melting. In other words, the temperature‐dependence curve of the diffraction intensity showed a peak that is interpreted as proof of the recrystallization in the melting process. The peak temperature was 216 °C. The temperature‐dependence curve of the enthalpy change obtained by the integration of the DSC curve almost coincided with that of the diffraction intensity. The double melting behavior in the heating process of PBT is concluded to originate from the increase of crystallinity, that is, recrystallization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2005–2015, 2001     

The multiple melting endotherms from poly(butylene terephthalate)

The melting behavior of poly(butylene terephthalate) (PBT) has been investigated, and a simulation has been performed to determine whether the multiple melting endotherms observed during the thermal analysis of PBT can be explained by the simultaneous melting and recrystallization of an initial distribution of crystal melting temperatures that contains only one maximum and two inflection points. Specimens that were cooled at constant rates from the melt showed between one and three melting endotherms upon heating in a differential scanning calorimeter (DSC). The position and breadth of the crystallization exotherms upon cooling from the melt and small-angle x-ray scattering showed that as the cooling rate is increased, the distribution of melting temperatures broadens and shifts to lower temperatures. By combining temperature-dependent recrystallization with an initial distribution of melting temperatures, simulated DSC curves were produced that agreed well with experimental DSC curves. In instances of triple peaked curves, the high temperature peak was due to crystals formed during the scanning process, and the middle and low temperature peaks were due to crystals originally present in the material. Satisfactory agreement between the experimental and simulated curves was found without considering additional crystallization from the amorphous regions during the scanning process.     

Study on the improvement of crystallization of high density polyethylene through dynamic packing injection molding

To better understand the effect of high‐density polyethylene on crystal morphology under the shear stress field, the dynamic packing injection molding was used to prepare the oriented pure polyethylene. In this present work, dynamic packing injection molding can exert a successive shear field on the melt in the mold cavity during packing stage. The structure of the samples was characterized through differential scanning calorimetry, wide‐angle X‐ray diffraction, and scanning electron microscopy. The oriented lamellae perpendicular to the flow direction can be formed. Oscillating stress between the lower and upper critical values can induce shish forming. The shish kebabs can be generated through sufficient relaxation led by slow cooling and suitable shear. We roughly discuss the relationship between the shear rate and crystal shape. Our results set up a method to reinforce polymer parts by regulating morphology and structure which can be used to do practical processing condition. Copyright © 2016 John Wiley & Sons, Ltd.     

Thermal and X‐ray analysis of polymorphic crystals,melting, and crystalline transformation in poly(butylene adipate)

Polymorphic crystals and complex multiple melting behavior in an aliphatic biodegradable polyester, poly(butylene adipate) (PBA), were thoroughly examined by wide‐angle X‐ray diffraction (WAXD) and differential scanning calorimetry (DSC). Further clarification on mechanisms of multiple melting peaks related to polymorphic crystal forms in PBA was attempted. More stable α‐form crystal is normally favored for crystallization from melt at higher temperatures (31–35 °C), or upon slow cooling from the melt; while the β‐form is the favored species for crystallization at low temperatures (25–28 °C). We further proved that PBA crystallization could also result in all α‐form even at low temperatures (25–28 °C) if it crystallized with the presence of prior α‐form nuclei. PBA packed with both crystal forms could display as many as four melting peaks (P1 ? P4, in ascending temperature order). However, PBA initially containing only the α‐crystal exhibited dual melting peaks of P1 and P3, which are attributed to dual lamellar distributions of the α‐crystal. By contrast, PBA initially containing only the β‐crystal could also exhibit dual melting peaks (P2 and P4) upon scanning. While P2 is clearly associated with melting of the initial β‐crystal, the fourth melting peak (P4), appearing rather broad, was determined to be associated with superimposed thermal events of crystal transformation from β‐ to α‐crystal and final re‐melting of the new re‐organized α‐crystal. Crystal transformation from one to the other or vice versa, lamellae thickening, annealing at molten state, and influence on crystal polymorphism in PBA were analyzed. Relationships and mechanisms of dual peaks for isolate α‐ or β‐crystals in PBA are discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1662–1672, 2005