Production of foam plastics by using environmentally benign blowing agents

微孔塑料（Microcellular Plastics，MP）是一种新型的泡沫塑料材料，其内部含有许多非常小的泡孔。与传统泡沫塑料相比，这种材料具有许多优点，如上级的热性能、机械性能和电性能，以及由于使用了二氧化碳和氮气等无害气体而使生产工艺和产品环保。本文研究了饱和压力、温度和压力对MP的影响。研究了在以二氧化碳和氮气为发泡剂的间歇式聚苯乙烯泡沫塑料生产中，饱和温度、减压速率、开始加热时间、加热温度和加热时间对泡孔结构（平均泡孔直径、泡孔数密度和发泡比）的影响。实验主要在高于聚合物玻璃化转变温度的高温下进行，其中操作工业生产工艺。本工作提出了一种“快速加热”方法，即在高压室中连续进行溶解、减压和加热过程。该方法能有效地利用溶解气体进行发泡，并能广泛地控制泡孔结构。结果发现，增加压力（气体溶解度）增加了泡孔的数量密度并减小了平均泡孔直径，增加温度对不同气体的影响不同，增加减压速率增加了泡孔的成核速率，减压和加热过程之间的短间隔导致较大的泡孔直径，并且在高温下加热首先增加细胞直径，但随后减小。通过对经典的成核理论和泡孔生长理论的推广，并考虑聚合物-气体混合物的各种性质，定性地描述了工艺条件与泡孔结构之间的关系。

Microcellular plastics (MP) is a newly innovated foam plastic material that includes numerous cells of very small sizes in it. This material has many advantages over conventional foam plastics, such as superior thermal, mechanical and electrical properties, as well as environmentally accepted production process and product because of using benign gases such as carbon dioxide and nitrogen.In this study the effects of saturation pressure, saturation temperature, decompression rate, time to start heating, heating temperature and heating time on the cell structure (average cell diameter, number density of cells and expansion ratio) were studied in batch-wise production of foam polystyrene using carbon dioxide and nitrogen as blowing agents. The experiments were carried out mainly at high temperatures above the glass transition temperature of the polymer where industrial production processes are operated. This work proposed a "quick heating" method, in which dissolution, decompression and heating processes are performed continuously in a high-pressure chamber. This new method could utilize the dissolved gas for foaming effectively and control the cell structure widely. As a result, it was found that increasing pressure (gas solubility) increases number density of cells and decreases average cell diameter, that the effect of increasing temperature is different for different gases, that increasing decompression rate increases the nucleation rate of cells, that short interval between decompression and heating processes results in the larger cell diameter, and that heating at high temperatures first increases cell diameter but decreases it later. Furthermore, the relationship between process conditions and cell structure was expressed qualitatively by extending classical nucleation theory and cell growth theory and by considering various properties of the polymer - gas mixture accurately.