发泡工艺对超临界CO_2/PLA微孔发泡泡孔形态的影响

研究了超临界CO2/PLA微孔发泡过程中,发泡温度、饱和压力、剪切速率对聚合物PLA泡孔形态的影响。结果表明,发泡温度对泡孔形态影响很大,温度降低,熔体强度增加,泡孔塌陷和合并减少,发泡材料的泡孔密度增大,泡孔尺寸减小,但温度太低时,熔体黏度和表面张力增加,发泡样品泡孔密度较低,泡孔壁较厚;压力对发泡形态的影响也是很显著的,压力太低,CO2的溶解度小,泡孔壁厚,泡孔分布不均匀。随着压力升高,CO2的溶解度增加,发泡样品的泡孔密度增加,泡孔更加均匀;随着转子转速增加,泡孔尺寸减小,气泡成核密度增大。但是转子转速过快,泡孔沿剪切的方向被拉长,泡孔取向严重,泡体质量变差。     

β成核剂对聚丙烯发泡材料的结晶行为和发泡性能的影响

在聚丙烯(PP)中加入β成核剂(TMB-5),以超临界二氧化碳(CO2)作为发泡剂,用高压发泡釜对其进行间歇发泡。研究β成核剂用量、饱和温度、饱和压力对β成核/PP发泡材料的结晶和发泡性能的影响。结果表明,β成核剂有效促进了β晶的形成,发泡材料中β晶相对含量最高可达到92.4%,但增大饱和压力却会抑制β晶产生。β成核剂同时起到异相成核作用,使泡孔成核更容易,制得的样品发泡性能较好。另外,饱和温度的升高会使PP熔体强度降低,导致泡孔的尺寸增大、密度减小;而随着饱和温度降低,饱和压力升高,气体在熔体中的溶解度增大,泡孔成核数量增多,使泡孔密度增大、泡孔尺寸减小。饱和压力为22 MPa时,泡孔密度可达2.72×108个/cm3。     

聚丙烯物理法微孔发泡操作条件与泡孔形态的关系研究

以超临界CO2流体和丁烷为发泡剂,用快速释压的方法,对PP的微孔发泡进行了研究,得到了泡孔密度达10^9泡孔／cm^2,泡孔直径为20-50μm的微孔泡沫塑料颗粒。研究表明,改变饱和压力和温度可以控制发泡的泡孔结构和密度。使用CO2为发泡剂,当温度低于90℃或压力低于6．0MPa时,PP很难出现发泡。提高温度使泡孔出现五边形的结构但泡孔尺寸增大;增加饱和压力,泡孔密度增加,泡孔直径减小。用超临界CO2流体和丁烷作发泡剂时所得到的泡孔密度分别为2．0×10^8-10^9和2．0×10^5—10^7泡孔／cm^3,泡孔平均尺寸分别为20—50μm和100—500μm。用超临界CO2流体和丁烷混合气体作为发泡剂时泡孔直径则出现了双峰分布的结构;加入成核剂炭黑后所得到的泡孔尺寸大于未加成核剂的情况,其泡孔密度和泡孔直径分别为7．0×10^6—1．6×10^9泡孔／cm^3和55—300μm。     

PP/超临界CO2连续挤出发泡成型

以超临界CO2为发泡剂,在连续挤出发泡过程中研究了超临界CO2用量对高熔体强度均聚聚丙烯(PP)发泡成型过程的影响.随着超临界CO2用量的增加,发泡挤出机口模压力降低,试样发泡倍率降低,泡孔尺寸变小,泡孔密度提高.在w(CO2)为3%,5%时,得到发泡倍率最高为13左右的PP发泡材料.w(CO2)为7%,发泡温度为12...     

加工参数及配方对PP/LLDPE共混物泡孔形态的影响

采用高压毛细管流变仪对不同含量碳酸钙(CaCO3)的聚丙烯/线型低密度聚乙烯(PP/LLDPE)共混物的流变性能进行了表征;并利用自制的实验装置,在不同发泡温度和饱和压力下,对共混物进行了超临界CO2模拟挤出发泡实验研究。结果表明:使用高熔体强度聚丙(烯HMSPP)发泡可以获得较好的泡孔形态;添加成核剂CaCO3可以使发泡试样的泡孔结构更加规则,泡孔分布更加均匀;随着CaCO3含量的增加,共混物的稠度上升,非牛顿指数降低,当CaCO3含量为3%时,共混物的发泡效果较好;130℃为最佳发泡温度,此时发泡试样的结构完整尺,寸均匀;随着饱和压力的增加发,泡试样的泡孔密度也有所提高。     

超临界CO2/PS静态发泡参数的研究

研究了超临界条件下CO2在PS中的溶解度、发泡PS膨胀率、玻璃化转变温度和泡孔密度、尺寸等与压力、温度的关系。结果表明：压力的增加，使CO2在PS中的溶解度增加；塑料膨胀率与压力和温度双参数的结合有关，当压力大于9MPa，而温度大于80℃时，PS才开始膨胀；经过CO2溶胀后，PS的玻璃化转变温度为80-95℃，比纯PS的低10-25℃；泡孔密度随压力的增加而增加，随温度的增加而减少；泡孔尺寸则随压力的增加而减小。     

聚丙烯/聚乙烯共混物超临界流体微孔发泡中黏弹性对泡孔结构的影响

密度低、刚度-质量比高、冲击强度高等优点使微孔发泡塑料越来越多地应用在工程领域,然而微孔塑料加工中依旧存在着一些困难需要解决,尤其是如何控制泡孔形态.文章采用4种不同熔体指数的聚乙烯(PE)分别对PP进行共混改性,并测量其流变性能,然后利用高压釜进行微孔发泡,旨在研究不同发泡压力下,熔体黏弹性对泡孔形态的影响.结果显示熔体强度和黏度低会使泡孔结构变差,尤其在较高的发泡压力下;而较大的熔体弹性和熔体强度更有利于形成较好的泡孔结构.     

超临界CO_2微孔发泡PE–LLD/PE–UHMW共混物

研究了线型低密度聚乙烯(PE–LLD)/超高分子量聚乙烯(PE–UHMW)共混物的超临界CO2微孔发泡行为,探讨了PE–UHMW含量、发泡温度和饱和压力对泡孔形貌的影响。采用差示扫描量热仪和旋转流变仪对PE–LLD及其共混物的热性质和流变性质进行了测试和表征,并通过扫描电子显微镜表征和分析了发泡样品的泡孔形貌。结果表明,少量PE–UHMW的加入可以显著降低PE–LLD发泡样品的孔径,增加孔密度。随着发泡温度的升高,PE–LLD样品的泡孔结构会发生塌陷现象,而加入少量PE–UHMW可以提高基体的黏度,起到支撑孔壁防止塌陷的作用,并最终得到均匀的开孔结构。另一方面,当温度一定时,饱和压力升高可以降低孔径并且得到开孔形貌的泡孔结构。     

不同聚丙烯材料共混的微孔发泡成型研究

聚丙烯(PP)熔体强度低,发泡性能差.将两种PP材料共混来改善PP的发泡性能,研究PP材料性质对共混体系微孔结构的影响.研究表明在各种发泡温度下使用纯PP材料很难制得泡孔结构好的微孔材料,而两种PP材料共混以后再进行微孔发泡,泡孔结构得到了改善.与两种相似熔点和黏度的PP共混材料相比,在高黏度的PP中混入少量的低熔点、低黏度PP时,可以制得泡孔结构更好的微孔材料.研究了共混比例对泡孔形态的影响,并从熔体黏弹性和结晶性能两方面分析了泡孔结构变化的机理.     

超高分子量聚乙烯超临界CO_2间歇发泡研究

应用超临界CO_2间歇发泡方法研究了温度、压力以及不同发泡工艺对超高分子量聚乙烯(UHMWPE)发泡的影响。结果表明:合适的饱和温度可以提高发泡倍率,减小泡孔尺寸,增加泡孔密度;发泡倍率和泡孔密度与饱和压力成正相关;对比不同工艺条件下的发泡结构与尺寸,得出正向发泡的泡孔尺寸小、泡孔密度高,而逆向发泡的泡孔尺寸大,但发泡倍率高。DSC结果表明:正向发泡的结晶度较高,发泡时异相成核数量增加,从而使泡孔尺寸减小、泡孔数量增加。比较正向和逆向发泡相同发泡倍率下的泡沫压缩性能,发现逆向发泡泡沫的弹性模量大于正向发泡泡沫。     

Foaming of Homogeneous Polypropylene and Ethylene-Polypropylene Block Copolymer Using Supercritical Carbon Dioxide

A new process was used to foam homogeneous polypropylene (HPP) and ethylene-polypropylene block copolymer (CPP). Many different foaming behaviors of these two kinds of PP were observed. The HPP and CPP were characterized by Differential Scanning Calorimetry (DSC), and Capillary Rheometry. We find that the melt shear viscosity of CPP is more sensitive to the temperature variation than that of HPP, thus leading to larger change of cell diameter of CPP with foaming temperature. Cell size of CPP is the result of competition between cell nucleation and cell growth. When the saturation pressure is lower or higher than 25 MPa, cell nucleation or cell growth plays a dominant role, which leads to the increase or decrease of cell size, respectively. Because of its low melting temperature and crystallinity, cell diameter of CPP increases with the infiltration temperature increasing, which is opposite to those of HPP. And at the foaming temperature of 152°C or 158°C, cell diameter of CPP increases or decreases with an increase in foaming time, while that of HPP decreases with foaming time increasing at both foaming temperatures.     

组合发泡剂对聚丙烯发泡行为的影响研究

采用物理发泡剂和化学发泡剂的组合发泡剂对聚丙烯(PP)和高熔体强度聚丙烯(HMSPP)在自制的单螺杆串联单螺杆挤出发泡机组上进行挤出发泡试验。通过真密度计/开闭孔率测定仪和扫描电子显微镜对发泡制品的密度、发泡倍率和泡孔形态进行测试。研究结果表明,采用组合发泡剂后,大部分PP和HMSPP发泡制品的泡孔密度提高,发泡倍率增加,泡孔尺寸分布更加均匀,泡体结构优于单独使用物理发泡剂或化学发泡剂的发泡制品。     

Cell coalescence suppressed by crosslinking structure in polypropylene microcellular foaming

A series of crosslinked polypropylene samples with increased melt strengths were prepared via a copolymerization reaction, followed by melt processing. These crosslinked PP samples (PP‐Cs) were foamed by a temperature rising process using supercritical CO₂ as the physical blowing agent. The introduction of crosslinking structure resulted in PP‐Cs foams with well‐defined closed cell structure, decreased cell size, and increased cell density in comparison with a linear PP, which were attributed to the suppressed cell coalescence due to the significant increase in melt strength of PP‐Cs. Further increasing the crosslinking degree tended to enhance the suppression effect on the cell coalescence, and hence increase the cell density of PP foams under the same foaming conditions, especially at the longer foaming times. The well‐defined closed cell structure was observed at the foaming temperature of 170–250°C and saturation pressure of 12–20 MPa. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Foaming behavior of microcellular foam polypropylene/modified nano calcium carbonate composites

A new process was used to prepare microcellular foams with supercritical carbon dioxide as the physical foaming agent in a batch. The foaming temperature range of the new process was about five times broader than that of the conventional one. Characterization of the cellular structure of the original polypropylene (PP) and PP/nano‐CaCO₃ (nanocomposites) foams was conducted to reveal the effects of the blend composition and processing conditions. The results show that the cellular structure of the PP foams was more sensitive to the foaming temperature and saturation pressure variations than that of the nanocomposite foams. Uniform cells of PP foams are achieved only at a temperature of 154°C. Also, the low pressure of 20 MPa led to very small cells and a low cell density. The competition between the cell growth and cell nucleation played important role in the foam density and was directly related to the foaming temperature. Decreasing the infiltration temperature depressed the initial foaming temperature, and this resulted in significantly larger cells and a lower cell density. A short foaming time led to a skin–core structure; this indicated that a decrease in the cell size was found from skin to core, but the skin–core structure gradually disappeared with increasing foaming time. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

聚丙烯及聚苯乙烯发泡体系熔体密度的研究

通过高压毛细管流变仪测量聚丙烯发泡体系的PVT关系,得到一定压力和温度下聚丙烯发泡体系的熔体密度,用于分析发泡体系的毛细管流变特性。与聚苯乙烯和高冲击强度聚苯乙烯发泡体系的熔体密度进行了对比,研究并分析了温度、压力、发泡剂及成核剂含量对发泡体系熔体密度的影响。结果表明:发泡体系的熔体密度均随压力的增大而提高,随温度的升高而降低;在发泡气体的临界压力处,发泡体系的熔体密度产生突变;高压下,发泡剂与成核剂含量对熔体密度的影响很小。     

加工参数及配方对PP/SBS共混物泡孔形态的影响

以CO2为发泡剂,利用SEM、DSC等测试方法研究了聚丙烯/苯乙烯-丁二烯-苯乙烯共聚物(PP/SBS)共混物的发泡行为。结果表明:在PP基体中引入SBS能显著改善发泡样品的泡孔形态;引入聚二甲基硅氧烷(PDMS)后,共混物的泡孔尺寸降低,泡孔密度进一步增大;在高压力降速率下,共混物的泡孔形态进一步改善;当发泡温度降到105℃时,由于CO2的增塑作用,PP/SBS/PDMS共混物仍能充分发泡,而且泡孔结构更好,其泡孔密度3.4×109个/cm3,平均泡孔直径6μm左右。     

Effects of Process Variables on Microcellular Structure and Crystallization of Polypropylene Foams with Supercritical CO2 as the Foaming Agent—A Study of Microcellular Foaming of Polypropylene

The effects of process variables on the microcellular structure and crystallization of foamed polypropylene (PP) with supercritical CO₂ as the foaming agent were investigated in this article. The cell size increased and the cell density reduced with increased foaming temperature. Differently, both the cell diameter and cell density increased as saturation pressure increased. DSC curves showed that the melting peak was broadened when supercritical CO₂ foaming PP. Furthermore, the width at half-height of the melting peak increased, the melting peak moved to higher temperature, and the melting point and crystallinity enhanced as the foaming temperature lowered and the saturation pressure enhanced.     

山梨醇类成核剂对改性聚丙烯发泡性能的影响

以过氧化苯甲酰（BPO）为引发剂,经熔融挤出过程将苯乙烯（St）接枝到等规聚丙烯（iPP）上,同时加入山梨醇类成核剂［1,3:2,4二（对甲基卞叉）山梨醇,MDBS］,制备可发泡的iPP,并考查MDBS在其发泡过程中所起的作用。结果发现,St接枝到iPP上,降低了iPP的熔体流动速率,即提高了其熔体强度;在发泡过程中,MDBS起固定泡孔和泡孔成核的作用,使iPP泡沫具有规则完整的泡孔结构,且泡孔密度从纯iPP的1.1×10^7个/cm3增加到1.2×10^8个/cm3,适宜发泡温度范围拓宽至150~160 ℃。     

二叔丁基过氧化物对PS/超临界流体CO2挤出发泡的影响

在自行研制的超临界流体CO2挤出发泡实验装置上研究了二叔丁基过氧化物（DTBP）对聚苯乙烯（PS）/超临界流体CO2挤出发泡的影响。结果表明,当DTBP的含量大于0.5 %时,PS的重均相对分子质量急剧下降,发生剧烈降解,使PS的熔体黏度急剧下降。在机头温度为112 ℃,机头压力为4 MPa,DTBP的含量小于0.3 %时,挤塑聚苯乙烯泡沫（XPS）的表观密度下降幅度较大;当其含量大于0.3 %时,下降趋势减缓。DTBP的加入使XPS的弹性模量、压缩强度和弯曲强度增大,弯曲模量降低。