成核剂在微孔发泡过程中复合力场下的实验研究

研究了成核剂类型、成核剂粒度、成核剂含量、振动参数对微孔发泡塑料泡孔形态的影响.通过对模拟振动挤出过程PS发泡的实验研究表明加入适当的成核剂能较好地改善泡孔形态,同时振动力场的引入有利于成核剂的均匀分散,形成均匀致密的气泡.     

纳米碳酸钙含量对PS发泡塑料泡孔形态的影响

在PS中加入不同含量的纳米碳酸钙作为成核剂,用自制的动态发泡模拟机研究了纳米碳酸钙含量对PS发泡塑料泡孔形态的影响。研究发现,加入不溶性的纳米碳酸钙后,PS泡孔成核更容易;并且PS中纳米碳酸钙含量的不同会影响泡孔的形态。当含量低于3％(质量分数,下同)时,纳米碳酸钙含量越高,越有利于气泡成核;而含量超过3％时,则泡孔分布变得严重不均,泡孔合并现象严重,减小了泡孔密度。当含量为3％时,制得的发泡塑料泡孔密度为8．3×107个/cm3,泡孔直径为20μm。在成型过程中施加振动进行初步实验,发现振动有利于成核剂在熔体中的分散。在纳米碳酸钙含量为3％、振幅为25 μm、振频为2．5 Hz时,制得了泡孔密度为8．7×107个/cm3、泡孔直径为17 μm的发泡塑料。     

振动剪切场下超临界CO2／PS微孔塑料气泡成核的研究

以超临界CO2 为发泡剂 ,用自行研制的电磁动态发泡模拟机 ,将机械振动力场引入到PS微孔塑料成型过程中 ,初步研究了稳态剪切力场和动态剪切力场对微孔塑料气泡成核的影响。实验发现 ,提高转速可以提高熔体的剪切应力 ,从而提高气泡成核率 ,但不如施加振动效果明显。施加振动后 ,泡孔直径随振幅和振频的增加而减小 ,泡孔密度随振幅和振频的增加而提高。在低温 (13 0℃ )、低压 (9MPa)下制备出泡孔直径约为 2 0 μm、泡孔密度约为6× 10 7个 /cm3 的微孔塑料。     

振动作用对PS和PVC微孔塑料泡孔结构影响的研究

以超临界CO2为发泡剂，用动态发泡实验装置制备了PS和PVC微孔塑料，通过扫描电镜照片观察和研究了振动作用对PS和PVC微孔塑料泡孔结构的影响。结果表明，当剪切速率较低时，在PS发泡过程中施加较弱的振动作用即可显著提高泡孔密度，减小泡孔直径；而在PVC发泡过程中，只有施加相对较强的振动作用才能达到同样的效果。当剪切速率较高时，不论何种发泡体系，施加较弱的振动作用可以改善泡孔的形态；而施加较强的振动作用可能会产生较大的剪切热和脉动剪切应力，从而破坏泡沫的微孔结构。     

PVC微孔塑料加工工艺与泡孔结构及耐热性关系研究

以超临界CO2为发泡剂,用动态发泡实验装置在不同的发泡温度、气体饱和压力及振动频率和振幅等加工工艺条件下制备了聚氯乙烯(PVC)微孔塑料。研究发现,发泡温度存在着一个最佳温度范围,使得泡孔密度最大、泡孔尺寸最小;气体饱和压力越大,泡孔结构越好;当剪切速率较低时,在发泡过程中施加强振动作用能显著提高泡孔密度,减小泡孔尺寸,当剪切速率较高时,施加较弱的振动作用即可改善泡孔形态,而施加较强的振动作用可能会产生较大的剪切热和脉动剪切应力,从而破坏泡孔结构;PVC微孔塑料的维卡软化温度与泡孔结构有着密切的关系,泡孔密度越大、泡孔尺寸越小,维卡软化温度就越高。     

成核剂含量对PS发泡复合材料泡孔形态的影响

在聚苯乙烯(PS)加入不同含量的成核剂,用自行研制的动态发泡模拟机研究了成核剂含量对PS发泡复合材料泡孔形态的影响。研究发现,成核剂有助于PS发泡材料形成大量成核点,泡孔成核更容易;并且PS中成核剂的含量不同会影响泡孔的形态,在发泡过程中尽量促进成核剂的分散,使体系内聚合物熔体、发泡剂和成核剂尽量均化,可以增加成核点数量并使泡孔分布均匀,改善泡孔形态。     

聚丙烯微孔复合材料的研究

采用模压发泡法制备聚丙烯微孔复合材料,用扫描电镜对发泡样品的微观结构进行表征,研究了发泡剂、成核剂等对微孔发泡材料泡孔结构的影响。结果表明:当滑石粉用量为15phr或木粉用量为30phr时,泡孔直径最小且,分布较均匀;在聚丙烯中加入蒙脱土可使泡孔直径减小、泡孔密度增加。     

振动力场作用下温度对超临界CO2/PS微孔塑料气泡形态的影响

以超临界CO2为发泡剂,用自行研制的动态发泡模拟机将机械振动力场引入到PS微孔塑料成型过程中,初步研究了振动力场作用下温度对微孔塑料气泡形态的影响.实验发现,发泡温度越高,气泡核长大的速度越快,导致气泡合并甚至破裂.但发泡温度过低时,超临界CO2在PS熔体中的扩散速率较低,最终制品的泡孔密度小,气泡分布也不均匀.在微孔塑料成型过程中施加振动,有利于发泡剂在熔体中的分散和混合,从而在较低的温度(130℃)下制备出泡孔直径为18μm、泡孔密度为7×107个/cm3的微孔塑料.     

超临界N_2微孔发泡PA6的制备及性能研究

采用超临界N2微孔发泡注射成型方法制备微孔发泡尼龙(PA)6材料,研究了注射温度、成核剂含量对泡孔密度、直径的影响。采用扫描电子显微镜考察了注射温度对泡孔大小、密度以及分布的影响。结果表明,随着注射温度的升高,泡孔直径变大,泡孔密度减小;成核剂含量增加泡孔密度变大,成核剂到达一定含量后泡孔密度增大不显著,成核剂含量对泡孔直径无显著影响。     

动态发泡工艺参数对PS微孔塑料泡孔结构的影响

以超临界CO2为发泡剂,用振动诱导发泡模拟装置研究了微孔塑料动态成型过程中气体饱和压力、压力释放速率、温度、气体饱和时间、稳态剪切速率、振动等工艺参数对聚苯乙烯（PS）微孔塑料泡孔结构的影响。研究发现,PS微孔塑料试样的泡孔结构随着气体饱和压力和压力释放速率的提高而得到改善,而温度、气体饱和时间、稳态剪切速率则存在一个最佳的操作范围,在此范围内制得的PS微孔塑料试样泡孔密度最大,泡孔尺寸最小。在稳态剪切速率一定的情况下,通过施加振动可以进一步改善泡孔结构．     

Study of Vibration Field on Microcellular Foaming in Nucleating Agents

A novel microcellular processing experimental setup was developed in which various nucleation agents were added to foaming material (Polystyrene). The effect of the nucleation agents on cell morphology of foam plastics was studied in the vibration field. The effects of the processing conditions such as nucleating agents, particle size of the nucleating agents, content of the nucleating agents, and the vibration parameters on polystyrene cell morphology were investigated. The cell morphology was analyzed with a scanning electron microscope. The results showed that the samples blown with nucleating agents, in general, had larger cell density and much smaller cell size than the ones without nucleating agents. It is believed that the smaller nucleating agents will be helpful for the larger bubble densities and the smaller cell size. There is the optimum content range for the maximum bubble densities and the minimum average cell diameter in foaming processing with nucleating agents. In the range of vibration parameter, the cell density increases with an increase of frequency and amplitude, and the cell size is the reverse.     

无机粉体形状对微发泡聚丙烯材料发泡行为的影响

选取粒径约为20μm的针状MgSO4晶须、片层状云母粉和粒状SiO2,以5%的用量加入到聚丙烯(PP)中,在二次开模条件下制备微发泡PP复合材料;通过异相成核理论和粉体分布的特性,分析了无机粉体形状对微发泡PP复合材料发泡行为的影响。结果表明,片层状云母粉具有良好的相容性、比表面特性和异相成核作用,发泡效果理想;泡孔直径达到22.10μm左右、泡孔密度为6.92×108个/cm3;聚烯烃类材料发泡的成核剂中,以片层状的云母粉较为理想。     

聚合物纳米复合材料微孔发泡及其影响因素的研究概况

结合聚合物异相成核的空穴模型,分析了含添加剂的聚合物异相成核理论。纳米级添加剂粒子比微米级添加剂粒子具有更小的尺寸和更大的表面积,与聚合物基体的接触更加紧密,因此其发泡制品具有更好的泡孔结构和性能。分析了聚合物/粘土纳米复合材料用超临界CO2发泡过程的影响因素。结果表明,剥离型纳米复合材料具有更小的泡孔尺寸和更大的泡孔密度。聚合物纳米复合材料与连续挤出发泡过程的结合为微孔发泡提供了一项新的技术。     

超临界CO2发泡微孔塑料的研究进展

介绍了超临界CO2 的特性及作用,从微孔塑料成型过程中的气体溶解、气泡成核、气泡长大、泡孔定型4个阶段出发,阐述了超临界CO2发泡微孔塑料的机理。还综述了微孔塑料的间歇成型、挤出成型、注射成型等3种常用成型方法,重点讨论了温度、压力、时间及外力场对微孔塑料泡孔结构的影响,并对微孔塑料的未来发展趋势作出展望。     

聚醚酰亚胺均相成核发泡行为研究

以超临界CO₂为发泡剂,采用间歇式发泡技术制备了聚醚酰亚胺（PEI）微孔泡沫。通过改变发泡温度、发泡压力与样品浸泡时间等工艺条件,研究了PEI的均相成核发泡行为。实验还通过二次降压法制备了具有复合泡孔结构的PEI微孔泡沫材料。结果表明,复合泡孔结构提高了PEI微孔泡沫的发泡倍率,第一次压力降ΔP₁与第二次保压时间Δt₂是影响复合泡孔结构参数的重要影响因素。     

Multiplex shear stress‐induced nucleation in dynamic microcellular foaming process

The effect of multiplex shear stress on the cell nucleation during microcellular foaming process was investigated using a dynamic foaming experimental apparatus. The multiplex oscillatory shear, which is different from previous one‐dimensional screw shear in a “stable” extrusion foaming process, is applied to the polymer melt through an axially vibrated rotor. The experimental results show that, by superimposing an axial vibration on the rotating rotor, the cell density increases and cell size decreases significantly when the shear rate is low. Both the uniformity of cell size and cell distribution are improved under vibration when compared with that without vibration regardless of how the shear rate changes. In addition, a simplified nucleation model based on shear energy has been carried out to qualitatively investigate the effect of both the simple steady shear and the multiplex oscillatory shear on the cell nucleation. Experiments and theoretical predictions all show that cell nucleation could be greatly improved by superimposing the oscillatory shear when the nucleation driving force induced by the steady shear is insufficient. Finally, the shear heat generated by excessive shear and strong vibration should be considered carefully although the isothermal condition was supposed in the present model. POLYM. ENG. SCI. 46:1728–1738, 2006. © 2006 Society of Plastics Engineers.     

Preparation and characterization of microcellular thin polycarbonate sheets

A new method was developed for the microcellular processing of polycarbonate (PC) thin sheets by compression molding above PC's glass‐transition temperature and below its melting temperature within a few minutes. The effects of the foaming time, foaming pressure, foaming temperature, and foaming agent active ratio on the cell size, cell density, and relative density were studied. The structures of the microcellular PC foam were controlled in the foaming process by carefully choosing the foaming parameters. In addition, the thermal, dynamic mechanical thermal, and electrical properties of the microcellular PC foam were investigated. A differential scanning calorimetry analysis showed that the microcellularly processed PC may have a plastication effect. The variation of the storage modulus, loss modulus, and tan δ under dynamic mechanical thermal analysis was in accord with the calorimetry analysis. The measurement of the electrical property demonstrated that the insulation ability of the microcellular PC thin sheet was obviously enhanced and the dielectric strength of the microcellular PC foam was decreased compared to the unfoamed PC. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1760–1766, 2006     

ABS微孔发泡材料的制备与性能研究

利用化学交联模压法制备了丙烯腈–丁二烯–苯乙烯塑料(ABS)微孔发泡材料,研究了发泡剂偶氮二甲酰胺(AC)、活化剂氧化锌(ZnO)、交联剂过氧化二异丙苯(DCP)用量对ABS微孔发泡材料力学性能和泡孔结构形态的影响。结果表明,当AC为2份、DCP为0.15份、ZnO为0.2份时,制得的ABS微孔发泡材料的泡孔密度为1.31×108cells/cm3,平均泡孔尺寸为24μm,比强度达到44.7 N/tex,综合性能最佳,可以满足微孔发泡材料的要求。     

ABS微孔发泡材料气体扩散行为分析

采用化学交联模压法制备了丙烯腈-苯乙烯-丁二烯共聚物(ABS)微孔发泡材料,研究了发泡温度、发泡压力及发泡时间对ABS微孔发泡材料气体的扩散行为及泡孔结构的影响,结果表明:气体吸收量随着发泡温度、发泡压力和发泡时间的增加,先增大后减小;随着气体吸收量的增加,制品的泡孔尺寸逐渐减小,泡孔密度逐渐增大,增加气体吸收量有利于提高发泡效果。当发泡温度为170℃、发泡压力为10 MPa、发泡时间为12min时,泡孔密度约为2.87×108个/cm3,可满足工业上微孔发泡材料泡孔密度的要求。