聚丙烯发泡体系的挤出胀大和泡孔平均直径预测模型

利用改进后的毛细管流变仪研究了温度、发泡剂与碳酸钙含量对聚丙烯发泡体系挤出胀大和泡孔直径的影响。综合胀大比与毛细管数的关系，提出了聚丙烯发泡体系挤出胀大和泡孔平均直径的预测模型。与实验结果相比，发泡体系挤出胀大的预测值与实验测量结果的误差在5％左右，气泡平均直径的预测值与实验测量值的误差在10％左右，表明所提出的预测模型能正确预测实验值。     

聚合物/超临界流体发泡体系的泡孔生长过程模拟

通过建立泡孔生长的数学模型,求解聚合物/超临界流体发泡体系的控制方程,得到泡孔生长的规律及影响因素.以聚丙烯/超临界CO2发泡体系为例,通过调整温度、系统压力、扩散系数等参数,得到不同条件下聚丙烯/超临界CO2体系的泡孔生长情况,并分析了各参数对泡孔生长的影响.     

单甘脂对聚苯乙烯挤出发泡性能的影响

利用超临界二氧化碳挤出发泡法,研究了单硬脂酸甘油脂（GMS）母粒的添加量对聚苯乙烯（PS）发泡性能的影响。采用毛细管流变仪研究了GMS添加量对PS/GMS体系的流变特性的影响,观察并测试了发泡材料的微观泡孔结构。研究结果表明,GMS的添加会降低树脂的黏度。母粒中含有的多组分GMS和少组分乙烯-醋酸乙烯（EVA）共同影响制品的表观密度、平均泡孔直径和泡孔密度等参数。在GMS添加量为1.05%,EVA添加量为0.45%时,制品的平均泡孔直径最小,泡孔密度最大。     

聚苯乙烯微孔发泡挤出成型研究

利用自行研制的超临界二氧化碳微孔发泡实验装置,研究了聚苯乙烯(PS)和PS/改性聚苯醚(MPPO)共混体系的微孔发泡挤出过程.通过对样品微观结构的表征,总结出挤出压力与制品微观结构之间的关系在挤出过程中总的趋势是挤出压力越高,制品的泡孔直径越小,泡孔密度越大.并分析了改性聚苯醚对聚苯乙烯体系的影响.     

PP/CaCO3复合发泡材料泡孔形态预测模型的研究

用单螺杆挤出装置,以CO2为发泡剂,对聚丙烯（PP）/CaCO3复合材料进行挤出发泡;采用正交法设计实验,利用Design-Expert统计软件对实验数据进行统计处理,观察制品纵截面上泡体的形态变化,从而得到加工工艺参数对泡体形态的影响规律,回归拟合得到泡孔平均直径、面密度、形变程度和倾向角的预测模型,并进行实验验证;最后用回归模型求解出较合适的加工参数范围。结果表明,转速为46~52 r/min、机头温度为170 ℃、熔体温度为180~189 ℃、CaCO3含量为6.67 ％~7.9 %时,可得到较好的PP/CaCO3发泡制品。     

聚苯乙烯／超临界CO2发泡体系黏度的研究

采用理论分析与实验相结合的方法对聚苯乙烯（PS）／超临界CO2（SCCO2）发泡体系的黏度进行了研究。对塑料熔体中气体对黏度的影响以及PS／SCCD2发泡体系的黏度进行了理论分析，得出带有发泡剂的塑料熔体的黏度是温度、剪切速率、压力和熔体中所含发泡剂种类、浓度及分布状态等韵函数；根据实验及数据分析结果整理建立了PS／SCCO2发泡体系的黏度预测模型η=10α/βγ^n-1，并与实验测得黏度进行了比较，结果表明，误差不超过5％，该模型可以很好地预测PS／SCCO2发泡体系的黏度。     

PP/改性纳米CaCO3/AC复合挤出发泡体系泡孔形态预测模型的研究

以AC发泡剂对聚丙烯(PP)/改性纳米CaCO3发泡体系进行挤出发泡,对发泡体系进行单因素轮换法实验,通过观察纵截面泡孔形态,分析各工艺参数对泡孔形态的影响规律,利用正交实验与实验统计软件相结合的方法对实验数据进行回归,得到泡体平均直径、泡孔面积比的预测模型,并进行了实验验证.通过模型预测最佳的加工参数范围,可对实验和...     

PMMA的微孔发泡工艺研究

文章对超临界CO2/PMMA体系进行了静压条件下的发泡成型工艺研究.重点考察了升温法和降压法对PMMA发泡性能和泡孔结构的影响.试验结果表明升温法和降压法对聚合物的发泡性能有不同的影响.当表观密度相同时,升温法得到的平均泡孔直径小,泡孔密度大,但泡孔直径分布不均匀,降压法得到的泡孔直径大、泡孔密度低,但直径分布相对均匀.     

超临界CO2对聚乳酸挤出发泡的影响

采用一种半结晶聚乳酸（PLA）,利用双螺杆串联熔体泵系统,以超临界CO2为发泡剂,进行挤出发泡实验。研究了CO2含量对PLA泡沫密度、泡孔密度和泡孔直径的影响。结果表明,发泡剂CO2含量在7 %～10 %（质量分数,下同）之间时,得到表观密度最低为40 kg/m3、泡孔直径为285 μm、泡孔密度为1.5×106 个/cm3的低密度PLA泡沫。随着CO2含量的增加,PLA泡沫的初始结晶峰减小,结晶度升高,说明超临界CO2对PLA的结晶具有促进作用。     

微孔塑料挤出成型的研究

以超临界CO2作为物理发泡剂,对低密度聚乙烯(LDPE)进行了微孔发泡的研究。介绍了微孔塑料成型过程中聚合物/气体均相体系的形成、气泡成核和气泡长大及定型这三个步骤。并分析了加工工艺因素(温度、压力)等对制品中泡孔尺寸和密度的影响:泡孔直径随挤出压力的增加而减小;泡孔密度随压力的增加而增加;泡孔直径随压力降速率的增大而减小;泡孔密度随压力降速率的增大而增加;而适当提高温度有利于减小泡孔直径、增加泡孔密度。     

CO_2微孔发泡聚碳酸酯/聚苯乙烯

采用快速升温法,在相对较低的压力下制备聚碳酸酯(PC)/聚苯乙烯(PS)共混物的微孔发泡材料.获得的PC/PS共混物发泡材料的平均泡孔直径为4.3μm,泡孔密度为8.89 × 10~9个/cm~3,而在相同条件下制得的PC和PS发泡材料的平均泡孔直径分别为28.6μm和143.8 0μm,泡孔密度分别为2.23×10~7个/cm~3和3.6×10~5个/cm~3.并研究PC、PS和PC/PS共混物的CO_2吸附行为以及PC/PS共混物在不同温度下的泡孔形态,发现泡孔首先在PS相中成核并生长.     

木塑/超临界流体复合材料泡孔成核的数值模拟研究

以木塑/超临界二氧化碳（WPC/Sc-CO2）复合材料为研究对象,采用有限元分析软件Polyflow对不同尺寸的挤出发泡机头内的流场进行数值模拟,研究机头尺寸对WPC/Sc-CO2复合材料泡孔成核的影响。结果表明,增加挤出发泡机头内毛细管段长度对机头内压力降速率和泡孔成核点距离机头出口的位置影响很小;而减小挤出发泡机头内毛细管段直径可增加机头内压力降速率,同时使泡孔成核点的位置更靠近机头出口。     

Introducing water as a coblowing agent in the carbon dioxide extrusion foaming process for polystyrene thermal insulation foams

In this study, water was used as a coblowing agent in the carbon dioxide (CO₂) extrusion foaming process in a twin screw extruder. It enlarged cell size and thus lowered foam density for better thermal insulation. Different strategies have been studied including direct injection of water into the extruder with surfactants, extrusion foaming of water expandable polystyrene (WEPS) beads, and feeding water containing activated carbon (WCAC)/polystyrene (PS) pellets. It was found that WCAC/PS pellets provided the most stable and clean extrusion process, more uniform cell morphology, and better thermal insulation than other methods. POLYM. ENG. SCI., 50:1577–1584, 2010. © 2010 Society of Plastics Engineers     

Basic study of extrusion of polyethylene and polystyrene foams

A fundamental study of bubble morphology development and apparent rheological properties in foam extrusion is reported. The influence of melt temperature, die length/diameter ratio, and blowing agent level on the morphology are considered. Measurements of the influence of blowing agent on viscosity, extrudate swell, and end-pressure losses are described. The viscosity is reduced, but extrudate swell is increased. End-pressure losses were found to become very large relative to the die wall shear stress at low extrusion rates. These results were interpreted in terms of bubble development. The filling of molds by foaming melts was observed and is described.     

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。     

Cell structure and impact properties of foamed polystyrene in constrained conditions using supercritical carbon dioxide

To obtain cellular with small cell diameter, to control cell structure and to improve impact strength of foaming materials, the quick-heating method was applied for foaming polystyrene (PS) using supercritical CO₂ (Sc-CO₂) as physical blowing agent. Then, changes of cell structure and impact strength in microcellular foamed PS materials under constrained conditions were studied. The effects of foaming processing parameters, such as foaming temperature, saturation pressure and foaming time on the cell structure and impact strength of foamed PS in the constrained conditions were studied. The results showed that the Sc-CO₂ solubility and nucleation density in the constrained conditions were not influenced compared with those under free foaming conditions. However, cells in constrained foaming process are mostly circular and independent with thick cell walls; the phenomenon of cell coalescence and collapse was effectively eliminated under constrained conditions. In addition, cell diameters in constrained foaming process decrease with increase in foaming temperature and increase with increase in the foaming time. Compared with that in free foaming conditions, the cell growth was restrained dramatically under constrained conditions which resulted in smaller cell diameter. Moreover, higher impact strength could be obtained for foamed PS as foaming time was prolonged, foaming temperature was increased or saturation pressure was enhanced.     

Investigation of the nanocellular foaming of polystyrene in supercritical CO2 by adding a CO2‐philic perfluorinated block copolymer

Nanocellular foaming of polystyrene (PS) and a polystyrene copolymer (PS‐b‐PFDA) with fluorinated block (1,1,2,2‐tetrahydroperfluorodecyl acrylate block, PFDA) was studied in supercritical CO₂ (scCO₂) via a one‐step foaming batch process. Atom Transfer Radical Polymerization (ATRP) was used to synthesize all the polymers. Neat PS and PS‐b‐PFDA copolymer samples were produced by extrusion and solid thick plaques were shaped in a hot‐press, and then subsequently foamed in a single‐step foaming process using scCO₂ to analyze the effect of the addition of the fluorinated block copolymer in the foaming behaviour of neat PS. Samples were saturated under high pressures of CO₂ (30 MPa) at low temperatures (e.g., 0°C) followed by a depressurization at a rate of 5 MPa/min. Foamed materials of neat PS and PS‐b‐PFDA copolymer were produced in the same conditions showing that the presence of high CO₂‐philic perfluoro blocks, in the form of submicrometric separated domains in the PS matrix, acts as nucleating agents during the foaming process. The preponderance of the fluorinated blocks in the foaming behavior is evidenced, leading to PS‐b‐PFDA nanocellular foams with cell sizes in the order of 100 nm, and bulk densities about 0.7 g/cm³. The use of fluorinated blocks improve drastically the foam morphology, leading to ultramicro cellular and possibly nanocellular foams with a great homogeneity of the porous structure directly related to the dispersion of highly CO₂‐philic fluorinated blocks in the PS matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012