高密度聚乙烯的过氧化物交联行为及结晶行为研究

采用过氧化物交联法分析了高密度聚乙烯（PE-HD）的交联行为,研究了过氧化二异丙苯（DCP）含量对PE-HD凝胶含量的影响,确定了最佳交联条件;采用差示扫描量热法和广角X射线衍射等测试技术研究了不同DCP含量对PE-HD结晶行为的影响。结果表明,随着DCP用量的增加,PE-HD的凝胶含量逐渐增加,当DCP用量高于1.5 %(质量分数,下同)时,凝胶含量增加缓慢,用量达到3.0 %时,凝胶含量可以达到73.9 %;当交联温度为170 ℃、交联时间为30 min时,DCP可完全分解,交联反应充分;随着DCP含量的增加,PE-HD的熔融温度、结晶温度及结晶度均呈下降趋势,晶粒尺寸变小,晶型未发生改变。     

过氧化物交联UHMWPE的动力学与结晶行为的研究

采用过氧化二异丙苯(DCP)交联改性超高相对分子质量聚乙烯(UHMWPE),通过差示扫描量热和广角X射线衍射测试,研究了DCP交联UHMWPE的反应动力学以及DCP含量对交联UHMWPE片材的热性能、结晶性能和晶粒尺寸的影响。结果表明:DCP与UHMWPE交联反应为放热反应,其非等温交联反应符合一级反应,反应活化能随着DCP含量的增加而降低;随着DCP含量的增加,交联UHMWPE片材的结晶度、重结晶度、熔点和结晶温度均降低,结晶峰强度和晶粒尺寸减小,当DCP质量分数为2. 5%时,交联UHMWPE片材(110)晶面和(200)晶面所对应的晶粒尺寸分别降低至18. 6 nm和12. 1 nm。     

过氧化物交联低密度聚乙烯的结构与性能关系研究

以过氧化二异丙苯(DCP)为交联剂,考察了温度、时间及DCP用量对交联低密度聚乙烯(XLDPE)结构和性能的影响,建立了结构与性能的关系。研究表明,交联度与交联密度随着DCP用量的增加而增大;当DCP用量超过2.0%,且交联温度和时间分别大于160℃和15 min时,XLDPE的交联度达到最大值;当温度高于450℃时,XLDPE热稳定性较LDPE好,且XLDPE的结晶度、结晶温度及熔融温度随着交联度的增加而下降;XLDPE具有剪切变稠特性,其剪切黏度随着剪切速率和交联度的增加而增大。     

BR／HDPE动态硫化共混体系橡塑并用材料的研究

以硫黄和DCP为交联剂,用动态硫化方法制备了BR/HDPE共混改性材料。当橡塑比为60/40～70/30时获得的热塑性弹性体,其伸但强度为10～20MPa,扯断伸长率350～520％,永久变形20～103％,硬度(邵氏A)76～90,炭黑对TPE有明显的补强效应,硫黄体系的TPE具有较大的扯断伸长率,而DCP体系的TPE的拉伸强度高,永久形变小,DCP可交联共混物中的BR和PE,使PE的结晶度降低。S和DCP交联体系共混物中PE的结晶度、结晶温度、非等温结晶的结晶能力、n值基本上不随BR量的多寡而变化,BR不影响PE的结晶机制。     

氯化聚乙烯橡胶改性聚丙烯的等温结晶动力学研究

用示差扫描量热仪(DSC)对氯化聚乙烯橡胶(CM)改性聚丙烯(PP)的等温结晶行为进行了研究。结果表明:交联体系影响结晶速度和结晶度,其中采用TCHC交联体系的结晶速度与结晶度均大于DCP交联体系的样品。相同温度下前者的Avrami方程n值与K值均大于后者。温度升高至135℃时,两体系的n值与K值都趋于一致,这说明交联剂在高温下对结晶影响减小。     

丙烯酸接枝线形低密度聚乙烯的热学行为及结晶形态

利用差示扫描量热仪研究了丙烯酸接枝线形低密度聚乙烯（PE-LLD-g-AA）的热学行为，结果表明，与纯线形低密度聚乙烯（PE—LLD）相比，PE-LLD-g-AA的熔融温度（Tm）略有增加，结晶温度（Tc）增加大约4℃，熔融焓（AHm）随AA含量的增加而降低。还利用差示扫描量热仪研究了PE—LLD和PE—LLD-g—AA的等温结晶动力学，用扫描电子显微镜观察了PE—LLD-g—AA等温结晶形态。结果表明，PE-LLD-g-AA的结晶速率大于纯PE—LLD的，随着接枝率的增加，PE-LLD的球晶半径减小，接枝到PE—LLD分子链上的AA分子起到了成核剂的作用。     

硅烷交联POE的非等温结晶动力学研究

通过差示扫描量热法（DSC）研究了乙烯-1-辛烯共聚物（POE）,过氧化二异丙苯改性POE和硅烷交联POE的非等温结晶动力学。应用Avrami法和莫志深法分别对POE,DCP改性POE和硅烷交联POE进行了非等温结晶动力学的计算。Avrami方法计算得到的结晶速率常数Zc和半结晶时间t1/2表明在同一降温速率下,随着POE的交联程度增加,Zc值减小,而t1/2则增大,结晶速率随POE交联程度的增加而降低,随降温速率增加而增加。莫志深方法计算结果表明,达到相同的结晶度,交联POE所需的降温速率要大于纯POE所需的降温速率,说明交联POE的结晶速率要低于纯POE的结晶速率。     

超临界CO2挤出发泡DCP微交联高密度聚乙烯研究

用过氧化二异丙苯(DCP)对高密度聚乙烯(PE-HD)进行微交联改性,采用熔体强度测定仪、差示扫描量热仪(DSC)对DCP微交联后PE-HD的熔体强度和结晶行为进行了表征。结果表明,添加少量DCP时,熔体强度不仅不能提高,反而下降,但是提高了PE-HD的结晶速率和结晶度;DCP添加量为0.5份时,体系的熔体强度最大,达0.127N,结晶度最低;用CO2的超临界流体作发泡剂对不同含量DCP微交联的PE-HD体系进行挤出发泡,用扫描电子显微镜和真密度计对其挤出发泡行为进行了研究。结果表明,在DCP添加量为0.5份时发泡效果最好,此时的泡孔较小,泡沫材料的密度可达0.5853g/cm3。     

BPO/DCP复合硫化体系对硅橡胶泡沫性能的影响

以BPO/DCP为复合硫化剂制备硅橡胶泡沫,研究了DCP用量对硅橡胶泡沫性能的影响规律.结果表明,在BPO/DCP复合硫化体系中,硅橡胶泡沫试样的密度、拉伸强度、撕裂强度没有随着DCP用量的增加而发生明显的变化;随着DCP用量的增加,试样的凝胶含量逐渐增大,当DCP用量超过1.5份时,硅橡胶泡沫的交联体系基本维持稳定;随着DCP用量的增加,硅橡胶泡沫材料的σ(ε=0.4)值先增后减,当DCP用量为2.O份时,σ(ε=0.4)值最大;DCP用量增加,硅橡胶泡沫试样的压缩应力松弛性能有降低的趋势,其DCP用量为1.5份时,压缩应力松弛性能最好;在松弛曲线的开始阶段(10 min以内)材料的载荷下降很快,随着时间的延长,载荷降低的速度明显降低,曲线逐渐趋于平缓;硅橡胶泡沫材料的短时间(20 min)应力松弛特征可以用公式Ft=F0(klogt+m)+at1/2+6来描述,拟合曲线与实验测试曲线具有较好的一致性.     

聚乳酸挤出发泡特性研究

使用过氧化二异丙苯(DCP)交联聚乳酸以提高它的熔体强度,采用单螺杆挤出机制备了聚乳酸发泡材料.使用转矩流变仪研究了不同DCP含量PLA交联体系的流变性能;通过DSC测试研究了纯PLA及交联PLA体系的熔融以及结晶过程;同时研究了发泡试样的泡孔结构.结果表明,DCP对PLA有交联和促进降解的作用,并促进了PLA的均相成核,但对改善PLA结晶性能没有很明显的作用.PLA交联之后,熔体强度有一定提高,在DCP含量为2.5份时发泡效果最好.     

Thermal characteristics and temperature profile changes of structurally different polyethylenes with peroxide modifications

Crosslinking and processing characteristics of polyethylenes (PEs) with different molecular architectures, namely high‐density polyethylene (HDPE), linear low‐density polyethylene (LLDPE), and low‐density polyethylene (LDPE), were studied with regard to the effects of peroxide modifications and coolant flow rates. Dicumyl peroxide (DCP) and di‐tert‐butyl peroxide (DTBP) were used as free‐radical inducers for crosslinking the PEs. The characteristics of interest included normalized gel content, real‐time temperature profiles and their cooling rates, exothermic period, crystallinity level, crystallization temperature, and heat distortion temperature. The experiments showed that LDPE exhibited the highest normalized gel content. The real‐time cooling rates, taken from the temperature profiles for all PEs before the crystallization region, were greater than those after the crystallization region. The cooling rate of the PEs increased with the presence of DCP, whereas the crystallization temperature of the PEs was lowered. The HDPE appeared to show the longest exothermic period as compared with those of the LLDPE and LDPE. The exothermic period showed an increase with increasing coolant flow rate, but it was decreased by the use of DCP. As for the effect of peroxide type, the gel content and cooling rate of the PE crosslinked by DCP were higher than those for the PE crosslinked by DTBP. The DTBP was the more effective peroxide for introducing crosslinks and simultaneously maintaining the crystallization behavior of the PE. J. VINYL ADDIT. TECHNOL., 20:80‐90, 2014. © 2014 Society of Plastics Engineers     

季铵盐类阳离子单体接枝聚丙烯及其性能研究

以甲基丙烯酞氧乙基三甲基氯化铵 ( DMC)、苯乙烯(St),聚丙烯(PP)为原料,采用多单体熔融接枝的方法,制备了含季铰盐基团的功能化的聚丙烯。考察了几种反应因素对接枝反应的影响,测试了接枝物的力学性能,利用示差扫描量热仪、偏光显微镜研究了接枝产物的结晶性能。结果表明:引发剂过氧化二异丙苯(DCP)用量为0.6份时,DMC与St的物质的量之比为1:1时,DM《的接枝效果最佳,与纯PP相比,其拉伸强度、冲击强度基本不变,晶核密度大幅增加,总结晶速率加快,半结晶时间((tm)缩短,结晶温度(Tc)提高。     

丙烯酸改性卤锑阻燃聚丙烯的结晶性能

研究了丙烯酸(AA)改性Sb2O3,聚丙烯(PP)母料制备的不同用量卤锑阻燃PP。阻燃PP的差示扫描量热法结果表明,阻燃剂在PP中存在明显的异相成核作用,使PP结晶温度提高,Sb2O3对PP的异相成核作用比十溴二苯醚明显。在无引发剂过氧化二异丙苯(DCP)存在下,AA对阻燃PP中PP结晶温度的影响取决于阻燃剂的用量;在DCP存在下,PP的结晶温度不随AA用量增加而改变。DCP用量增加导致PP严重降解,结晶温度与熔融温度降低。     

Crosslinking of polypropylene–polyethylene blends by peroxide and the effect of pentaerythritol tetrallyl ether

Crosslinking of polypropylene–polyethylene (PP-PE) blends involving 10, 20, 30, 40, 50, 60, 70, 80, and 90% of PP with dicumylperoxide (DCP) or tert-butyl perbenzoate (TBPB) and in the presence of coagent pentaerythritol tetrallyl ether (PETA) was investigated at 180°C. It was found that at lower concentrations of peroxide alone (e.g., 2.5% of DCP) only PE component is crosslinked in all compositions of PP-PE blends. In the crosslinking of PP-PE 50:50 with 4% of TBPB, insoluble gel was obtained, which contained 13% PP and 87% PE. If 2% PETA was also used, the portion of PP in gel increased to 39%; the total yield of gel in PP-PE blend increased from 50 to 70%. The lower crosslinking efficiency of coagent PETA in the PP-PE blends compared with PP alone is associated with better solubility of the coagent in the PE phase in contrast to the PP phase. The coagent does not particularly raise the crosslinking efficiency of peroxide in PE, but increases it in the PP phase. A remarkable decrease in melting temperature and temperature of crystallization of both polymer components depending on peroxide concentration was found by calorimetric measurements.     

Thermal and morphological characterization of composites prepared by solution crystallization method of high‐density polyethylene on carbon nanotubes

The morphology, nucleation, and crystallization of polyethylene/carbon nanotubes composites prepared by solution crystallization method of high density polyethylene on Multiwall Carbon Nanotubes (MWNTs) are studied. Transmission electron microscopy (TEM) results show that the center stems of MWNTs are decorated with lamellar crystals. The nonisothermal crystallization kinetics of pure PE and PE/MWNTs composites are investigated by differential scanning calorimetry at various cooling rates. It is found that the Avrami analysis modified by Jeziorny and Mo can describe the nonisothermal crystallization process of pure PE and PE/MWNTs very well. The difference in the value of exponent between PE and PE/MWNTs suggests that addition of the MWNTs influences the mechanism of nucleation and the growth of PE crystallites. On one hand, the increasing of temperature corresponding to the maximum rate of crystallization and the onset crystallization temperature and the study of the nucleation activity reveal that the inorganic component (MWNTs) can act as the nucleating agent to facilitate the crystallization of PE in the hybrids. On the other hand, the decreasing degree of crystallinity and the increasing of half‐crystallization time imply that the MWNTs networks confine the crystallization of PE. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Crystallization and melting behavior of nano‐CaCO3/polypropylene composites modified by acrylic acid

Nano‐CaCO₃/polypropylene (PP) composites modified with polypropylene grafted with acrylic acid (PP‐g‐AA) or acrylic acid with and without dicumyl peroxide (DCP) were prepared by a twin‐screw extruder. The crystallization and melting behavior of PP in the composites were investigated by DSC. The experimental results showed that the crystallization temperature of PP in the composites increased with increasing nano‐CaCO₃ content. Addition of PP‐g‐AA further increased the crystallization temperatures of PP in the composites. It is suggested that PP‐g‐AA could improve the nucleation effect of nano‐CaCO₃. However, the improvement in the nucleation effect of nano‐CaCO₃ would be saturated when the PP‐g‐AA content of 5 phf (parts per hundred based on weight of filler) was used. The increase in the crystallization temperature of PP was observed by adding AA into the composites and the crystallization temperature of the composites increased with increasing AA content. It is suggested that the AA reacted with nano‐CaCO₃ and the formation of Ca(AA)₂ promoted the nucleation of PP. In the presence of DCP, the increment of the AA content had no significant influence on the crystallization temperature of PP in the composites. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2443–2453, 2004     

低密度聚乙烯/石墨烯纳米复合材料非等温结晶动力学

采用差示扫描量热仪研究了不同石墨烯(GP)含量的低密度聚乙烯(PE–LD)纳米复合材料在不同降温速率下的非等温结晶行为。结果表明,不同含量GP填料的加入均导致PE–LD结晶温度提高,表明GP填料对PE–LD基体起到异相成核作用;莫志深法能很好地描述纳米复合材料的动态结晶行为。动力学数据显示,当GP质量分数为0.5%和2%时,PE–LD复合材料的整体结晶速率、活化能、成核常数和生长晶面的表面自由能均比纯PE–LD低,而含量为5%时其值均比纯PE–LD高,因此适量的GP有利于PE–LD的结晶。由成核常数、表面自由能值可看出低含量GP促进PE–LD晶粒的二次成核、生长,而高含量GP则抑制晶粒二次成核、生长。     

Reactive compatibilization and performance evaluation of miscanthus biofiber reinforced poly(hydroxybutyrate‐co‐hydroxyvalerate) biocomposites

Dicumyl peroxide (DCP) initiated reactive compatibilization of poly(hydroxybutyrate‐co‐hydroxyvalerate) (PHBV)/miscanthus fibers (70/30 wt %) based biocomposite was prepared in a twin screw extruder followed by injection molding. In the presence of DCP, both the flexural and the tensile strength of the PHBV/miscanthus composites were appreciably higher compared with PHBV/miscanthus composite without DCP as well as neat PHBV. The maximum tensile strength (29 MPa) and flexural strength (51 MPa) were observed in the PHBV/miscanthus composite with 0.7 phr DCP. The enhanced flexural and tensile strength of the PHBV/miscanthus/DCP composites are attributed to the improved interfacial adhesion by free radical initiator. Unlike flexural and tensile strength, the modulus of the PHBV/miscanthus/DCP composites was found to slightly lower than the PHBV/miscanthus composite. The modulus difference in the PHBV/miscanthus composite with and without DCP has good agreement with the observed crystallinity. However, the flexural and tensile modulus of all the prepared biocomposites was at least two fold higher than the neat PHBV. The storage modulus value of the PHBV/miscanthus and PHBV/miscanthus/DCP biocomposites follows similar trend like tensile and flexural modulus. The melting temperature and crystallization temperature of PHBV/DCP and PHBV/miscanthus/DCP samples were considerably lower compared with the neat PHBV and PHBV/miscanthus composites. The surface morphology revealed that the PHBV/miscanthus/DCP composites have good interface with less fiber pull‐outs compared with the corresponding counterpart without DCP. This suggests that the compatibility between the matrix and the fibers is enhanced after the addition of peroxide initiator. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44860.     

On the nonisothermal melt crystallization kinetics of industrial batch crosslinked polyethylene

The chemical modification of commodity polymers such as polyethylene (PE) is a versatile synthetic approach for preparing materials that cannot be manufactured cost-effectively using conventional polymerization techniques. Aiming to improve PE character low contents of dicumyl peroxide (DCP), from 0% to 1.5% was added as crosslinker to an industrial batch (PEs mixture and additives). From tensile testing crosslinking provided higher elastic modulus most due to the restrained microstructure where XPEs macromolecular chains are interconnected also providing lower strain at break. Crosslinking effects on the nonisothermal melt crystallization rate (Cmax) and degree of crystallinity (Xc) were evaluated; Cmax increased with the cooling rates, whereas Xc increased upon DCP addition. The melt crystallization kinetics were thoroughly investigated applying Pseudo-Avrami, Ozawa, and Mo models. Ozawa failed to describe the crystallization most due to ignore the secondary crystallization and spherulites impingement at the end of crystallization while Pseudo-Avrami and Mo provided quite good fits. The activation energy was computed using Arrhenius' approach, crosslinked compounds presented higher energy consumption, whereas exception was verified for 0.5XPE which displayed the lowest energy and overall the best mechanical performance this is the most proper compound for industrial applications, such as packaging, and disposables as well as general goods.     

Investigation on the structure and crystallization behavior of controlled-rheology polypropylene with different stereo-defect distribution

Understanding concerning the influence of peroxide degradation on the stereo-defect distribution and related crystallization kinetics of controlled-rheology polypropylene are of great importance. In this study, two iPP samples (PP-A, PP-B) with similar molecular weights and average isotacticities, but different stereo-defect distributions and their degradation productions after the addition of dicumyl peroxide (DCP) were prepared. Their melt flow indexes (MFI), stereo-defect distributions, crystallization behaviors and kinetics were studied using MFI measurement, differential scanning calorimetry, wide-angle X-ray diffraction, non-isothermal crystallization kinetics and successive self-nucleation and annealing fractionation. The results showed that as the content of DCP increased, the MFI, the crystallization temperature and crystallization rate of PP increased gradually, the crystallization peak width became narrower, and the crystallite size decreased. Meanwhile, the addition of DCP greatly restrained the formation of thick lamellae and narrowed its stereo-defect distribution [meso-sequence length (MSL) distribution]. On the other hand, results showed that PP resins with different stereo-defect distribution have similar MFI variations after degradation. PP-A (whose stereo-defect distribution was less uniform than PP-B) and its degradation products still possess higher crystallization rate, stronger crystallizability, smaller crystallite size and higher fractions of long MSL, compared with their counterparts of PP-B.