二丙烯酸酯参与的反应挤出制备长链支化PP

研究了二丙烯酸酯参与的反应挤出制备长链支化聚丙烯过程,重点考察了二丙烯酸酯双键间链段长度以及单体用量对长链支化程度的影响。结果表明,1,4-丁二醇二丙烯酸酯(BDDA)在聚丙烯分子链上具有较强接枝能力;在接枝率相当的情况下,悬垂双键参与偶合扩链的能力会随双键间链段长度增加而下降。单体接枝率增加以及悬垂双键反应能力增强均会使长链支化程度增大。随着二丙烯酸酯用量增加,长链支化程度增加;单体过量会使大分子自由基偶合扩链程度加重,导致局部交联形成凝胶。     

反应挤出制备长链支化聚丙烯：挤出条件对挤出物熔体性能的影响

本文采用在过氧化物和官能团丙烯酸单体共存的情况下通过反应挤出的方法对聚丙烯进行长链支化改性，通过引入一种支化促进剂抑制反应挤出过程中的β-断裂和交联。对制备的长支链聚丙烯进行了流变学研究。研究了原料聚丙烯种类、过氧化物的类型和浓度对挤出物熔体强度的影响。     

反应挤出制备高熔体强度PP

采用反应挤出方法制备高熔体强度聚丙烯,通过凝胶渗透色谱仪、差示扫描量热仪、偏光显微镜等研究了改性产品的结构与性能,并进行挤出发泡应用实验。结果表明：采用特殊的过氧化物引发剂和支化促进剂,与聚丙烯基础树脂共混后通过双螺杆挤出机熔融连续反应挤出,可以直接制备具有长链支化结构的聚丙烯,熔体强度提高300％;挤出发泡试样泡孔均匀,发泡倍率达到50倍,具有较好的可发性能。     

长链支化聚丙烯的反应挤出制备及其流变和热力学性能研究

在过氧化引发剂和季戊四醇三丙烯酸酯(PETA)存在下,采用反应挤出法制备了长链支化聚丙烯（LCB-PP）。用旋转流变仪和差示扫描热法系统研究了纯的和改性PP的流变性能和热力学性能,并考察了不同过氧化引发剂对改性PP的性能和支化情况的影响。研究发现,单纯使用过氧化引发剂改性时,PP以降解为主;加入多功能单体PETA后,PP以接枝反应为主。流变行为研究发现,过氧化引发剂/PETA改性的PP,其流变性能呈现如低频处储能模量增大,剪切变稀行为明显,损耗角随频率变化出现平台区,零剪切黏度增大等特点,证明改性PP存在长链支化结构,通过公式计算发现改性PP的支化度较高。差士扫描量热分析表明,过氧化引发剂/PETA改性PP的结晶温度高于纯PP,这也说明改性PP存在长链支化结构。同时发现过氧化引发剂/PETA改性PP时,过氧化引发剂结构对改性PP的流变性能、热力学性能和支化度影响较小。     

长链支化聚丙烯的研究进展

介绍了长链支化聚丙烯制备的成熟技术；阐述了长支链对聚丙烯熔体弹性影响的机理；分析了长链支化对聚丙烯结晶行为和流变行为的影响。当前的研究表明：长支链可以显著提高聚丙烯的熔体弹性。电子束辐射进行聚丙烯的长链支化受到辐射温度、辐射剂量以及辐射的条件和后处理工艺的强烈影响；反应挤出进行聚丙烯的长链支化受到过氧化物用量及其分子结构的影响。长链支化聚丙烯的结晶行为和流变行为与线形聚丙烯存在明显差异，其初始结晶温度要高于线形聚丙烯10℃左右；流变行为表现出显著的“应变硬化”现象，从而可以有效地保证挤出发泡过程中气泡增长的稳定。     

控制长链支化度对EPDM挤出性能的影响

生产高质量、低成本的ＥＰＤＭ制品需要彻底了解聚合物参数对加工和产品性能的影响。2 0世纪 90年代已有文献报道了对混炼和聚合物参数的研究 ,近年来的热门话题是挤出行为。测量的挤出参数包括 :功率消耗、产量、产量 /机头压力、比能耗、胶料最高温度和口型膨胀率。用化学组分、门尼粘度、相对分子质量分布和长链支化度描述了ＥＰＤＭ的分子结构。最近推出的新一代ＥＰＤＭ的分子结构与普通ＥＰＤＭ有很大不同 ,运用控制长链支化度原理获得了相对分子质量分布与长链支化度的平衡。这种聚合物是为改进混炼和挤出性能并保持较好的物理性能而…     

长链支化聚丙烯的制备及其熔体流变性能的研究

在过氧化物引发剂和季戊四醇三丙烯酸酯存在下,利用反应挤出法制备了长链支化聚丙烯(LCB-PP)。采用熔体流动速率(MFR)仪、旋转流变仪和熔体强度测试仪对纯聚丙烯(PP)及其改性PP进行测试与表征。讨论了不同的过氧化物引发剂对改性PP流变性能的影响。结果表明,采用过氧化苯甲酰时,改性PP具有较高的熔体强度、较低的MFR,并且在低频处储能模量增大。同时发现,随温度的升高,改性PP的熔体强度逐渐降低,但升高到一定温度后,熔体强度的变化不明显。     

长链支化制备高熔体强度PP的研究

通过长链支化来改性PP，从而得到高熔体强度的PP。实验以丙烯酸酯类单体为接枝单体，过氧化物为引发剂，对PP进行了熔融接枝，重点考察了二官能团单体的改性情况。实验结果表明，二三官能团单体的改性效果较为明显；熔体流动速率随单体加入量增加而降低，随过氧化物浓度增加而升高；拉伸粘度谱图显示有明显的应变硬化现象；改性后产物的熔体强度变化明显；纯化后的产物经工外，差示扫描量热分析表明接枝反应的发生；索氏萃取法没有检测到凝胶的生成。     

长链支化聚丙烯的制备及其流变性能研究

设计合成了3种不同结构的非对称双烯单体,作为制备长链支化聚丙烯的接枝单体。并通过旋转流变仪研究了所制备样品的流变性能,研究发现对烯丁基苯乙烯、对烯丁氧基甲基苯乙烯、丙烯酸烯丁酯抑制聚丙烯降解的能力依次减弱,其中对烯丁基苯乙烯和对烯丁氧基甲基苯乙烯适合用作制备长链支化聚丙烯的接枝单体。     

可控长链支化EPDM的性能及应用

介绍可控长链支化(CLCB)EPDM的性能和应用.CLCB EPDM兼具窄相对分子质量分布和高长链支化度,炭黑分散性和抗炭黑焦烧性良好,抗坍塌性和耐压缩永久变形性能优异,挤出和硫化速度快.与门尼粘度和相对分子质量分布相当的传统EPDM相比,CLCB EPDM挤出性能优异,在密封条等挤出制品中应用具有很大潜力.     

Supercritical carbon dioxide-assisted reactive extrusion for preparation long-chain branching polypropylene and its rheology

An environmental benign process, which uses supercritical carbon dioxide (ScCO₂) as a processing aid, is developed in this work to prepare long chain branching polypropylene (LCB-PP). Results from the oscillatory shear rheology, melt elongational behavior and Fourier transformed infrared spectroscopy (FTIR) show that long chains have been linked as branches to the original linear PP chains using scCO₂-assisted reactive extrusion in the presence of cumene hydroperoxide and 1,6-hexanediol diacrylate. Compared to the initial linear PP, the branched samples show higher storage modulus (G′) at low frequency, distinct strain hardening of elongational viscosity, lower melt flow rate, increased crystallization temperature and improvement of the melt strength. ScCO₂ can improve the branching efficiency of modified PPs. The elastic response, melt strength and strain hardening parameter of the modified PPs increase with increasing scCO₂ concentration, which is ascribed to scCO₂ acting as a plasticizer for reducing PP viscosity and a carrier for active chemical species.     

Rheology and thermal behavior of long branching polypropylene prepared by reactive extrusion

Long‐chain branching polypropylene (LCB‐PP) was achieved by reactive extrusion in the presence of bifunctional monomer [1,6‐hexanediol diarylate (HDDA)] and peroxide of dicumyl peroxide (DCP). Influences of HDDA and DCP concentrations on the branching efficiency were comparatively evaluated. Fourier transformed infrared spectroscopy (FTIR) results indicated that the grafting reaction took place, and HDDA has been grafted on PP skeleton. In comparison with initial PP, some modified samples showed lower melt flow index because of a large number of LCB in their skeleton. Several rheology plots were used to investigate the rheological properties of the initial PP and modified PPs, and the rheological characteristics confirmed the LCB in modified PPs skeleton. DSC results showed that the crystallization temperatures of modified PPs were higher than those of initial PP and degraded PP, suggesting that the modified PPs had long‐chain branched structure. The contrastive investigation in the rheology of modified PPs suggested that proper concentrations of HDDA and DCP were more beneficial to producing LCB during reactive extrusion. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

通过反应挤出提高聚丙烯的熔体强度

利用反应挤出技术研究了不同反应物对聚丙烯(PP)熔体强度的影响。考察了不同用量的低密度聚乙烯(LDPE)、乙烯-乙酸乙烯酯共聚物(EVA)、季戊四醇三丙烯酸酯(PETA)、二乙烯基苯(DVB)以及上述物质的混合物在过氧化二异丙苯的引发下对PP熔体强度、熔体流动速率、熔垂的影响。结果表明,LDPE、EVA的加入对产物熔体强度的影响有限,PFTA也只能使其提高1倍左右;而DVB的加入可使产物的熔体强度显著提高,仅加入1％就可使熔体强度提高20倍,熔垂实验也证明了这一点;几种反应物混合使用效果不如单独使用好。     

Influence of polyfunctional monomer on melt strength and rheology of long‐chain branched polypropylene by reactive extrusion

Long chain branching (LCB) were added to linear polypropylene (PP) using reactive extrusion in the presence of selected polyfunctional monomers (PFMs) and a peroxide of dibenzoyl peroxide (BPO). Fourier Transformed Infrared spectra (FTIR) directly confirmed the grafting reaction occurred during the reactive extrusion process. Various rheological plots including viscosity curve, storage modulus, Cole‐Cole plot, and Van‐Gurp plots, confirmed that the LCB structure were introduced into modified PPs skeleton after modification. In comparison with linear PP, the branched samples exhibited higher melt strength, lower melt flow index, and the enhancement of crystallization temperature. The LCB level in modified PPs and their melt strength were affected by the type of PFM used and could be controlled by the PFM properties and structure. PFMs with lower boiling points, such as 1, 4‐butanediol diacrylate (BDDA), could not produce LCB structure in modified PP skeleton. The shorter molecular chain bifunctional monomers, such as 1,6‐hexanediol diacrylate (HDDA), favored the branching reaction if their boiling points were above the highest extrusion temperature. And some polar groups, such as hydroxyl, in the molecule of PFM were harmful to the branching reaction, which might be attributed to the harm of the polarity of groups to the dispersion of PFM in PP matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

利用反应挤出的聚丙烯熔融接枝改性

系统简介了聚丙烯熔融接枝体系的组成、机理及实现熔融接枝的反应挤出技术。介绍了聚丙烯接枝物的表征和应用状况，并指出了熔融接枝体系中存在的问题。     

Preparation and characterization of high melt strength polypropylene with long chain branched structure by the reactive extrusion process

The reactive extrusion of maleic anhydride grafted polypropylene (PP‐g‐MAH) with ethylenediamine (EDA) as coupling agent is carried out in a corotating twin‐screw extruder to produce long chain branched polypropylene (LCBPP). Part of PP‐g‐MAH is replaced by maleic anhydride grafted high‐density polyethylene (HDPE‐g‐MAH) or linear low‐density polyethylene (LLDPE‐g‐MAH) to obtain hybrid long chain branched (LCB) polyolefins. Compared with the PP‐g‐MAH, PE‐g‐MAH, and their blends, the LCB polyolefins exhibit excellent dynamic shear and transient extensional rheological characteristics such as increased dynamic modulus, higher low‐frequency complex viscosity, broader relaxation spectra, significantly enhanced melt strength and strain‐hardening behaviors. The LCB polyolefins also have higher tensile strength, tensile modulus, impact strength and lower elongation at break than their blends. Furthermore, supercritical carbon dioxide (scCO₂) is constructively introduced in the reactive extrusion process. In the presence of scCO₂, the motor current of the twin extruder is decreased and LCB polyolefins with lower melt flow rate (MFR), higher complex viscosity and increased tensile strength and modulus can be obtained. This indicates that the application of scCO₂ can reduce the viscosity of melt in extruder, enhance the diffusion of reactive species, and then facilitate the long chain branching reaction between anhydride group and primary amine group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Grafting of maleic anhydride onto polypropylene by reactive extrusion

Maleic anhydride grafting onto polypropylene was conducted in a twin‐screw extruder according to an experimental design in which the maleic anhydride and peroxide concentrations were varied. The modified polypropylene was characterized by FTIR spectroscopy, melt‐flow index measurements, size‐exclusion chromatography, differential scanning calorimetry, and nuclear magnetic resonance. The results showed that only the independent variable peroxide concentration influenced the amount of reacted maleic anhydride, whereas the two variables studied influenced the molecular weight of the grafted polypropylene. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2706–2717, 2002     

Structure and melt rheology of long‐chain branching polypropylene/clay nanocomposites

Long‐chain branching polypropylene (LCB‐PP)/clay nanocomposites were prepared by melt blending in a twin‐screw extruder. The microstructure and melt rheology of these nanocomposites were investigated using x‐ray diffraction, transmission electron microscopy, oscillatory shear rheology, and melt elongation testing. The results show that, the clay layers are intercalated by polymer molecular chains and exfoliate well in LCB‐PP matrix in the presence of maleic anhydride grafted PP. Rheological characteristics, such as higher storage modulus at low‐frequency and solid‐like plateau in tan‐ω curve, indicate that a compact and stable filler network structure is formed when clay is loaded at 4 phr (parts per hundred parts of) or higher. The response of the nanocomposite under melt extension reveals an initial decrease in the melt strength and elongational viscosity with increasing clay concentration up to 6 phr. Later, the melt strength and elongational viscosity show slight increases with further increasing clay concentration. These results might be caused by a reduction in the molecular weight of the LCB‐PP matrix and by the intercalation of LCB‐PP molecular chains into the clay layers. Increases in the melt strength and elongational viscosity for the nanocomposites with decreasing extrusion temperature are also observed, which is due to flow‐induced crystallization under lower extrusion temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Alder Ene functionalization of polypropylene through reactive extrusion

A commercial isotactic polypropylene was degraded to increase its terminal vinylidene group concentration, and it was subsequently functionalized with maleic anhydride through the Alder Ene reaction at temperatures above 200°C in a co‐rotating twin screw extruder. Characterization of the maleated product by Fourier transform infrared spectroscopy, ¹H NMR, differential scanning calorimetry, and gel permeation chromatography showed the anhydride group to be terminally attached, and the degree of functionalization was determined by infrared analysis. Increased temperature and maleic anhydride concentration, as well as improved mixing in the extruder, were found to improve the extent of the reaction. The catalytic contribution of Lewis acid species was evaluated, and ruthenium chloride was found to increase the extent of the reaction by 16% in comparison with stannous chloride as a catalyst in the Alder Ene reaction. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 503–516, 1999