Production of foam plastics by using environmentally benign blowing agents

微孔塑料（MP）是一种新型的泡沫塑料材料，其中包含许多非常小尺寸的细胞。与传统泡沫塑料相比，这种材料具有许多优点，例如优越的热、机械和电气性能，以及由于使用二氧化碳和氮气等良性气体而对环境可接受的生产过程和产品。在以二氧化碳和氮气为发泡剂批量生产泡沫聚苯乙烯时，研究了饱和压力、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沫聚苯乙烯结构（平均孔径、孔数密度和膨胀比）的影响。实验主要是在高于聚合物玻璃化转变温度的高温下进行的，工业生产过程是在高温下进行的。本工作提出了一种“快速加热”方法，即在高压室内连续进行溶解、减压和加热过程。该方法可以有效地利用溶解气体进行发泡，广泛地控制胞体结构。结果发现，压力（气体溶解度）的增加增加了细胞的数量密度，降低了细胞的平均直径，温度的升高对不同气体的影响不同，减压速率的增加增加了细胞的成核速率，减压和加热之间的时间间隔短，导致细胞直径变大，高温加热先增加细胞直径，后减少细胞直径。进一步，通过对经典成核理论和细胞生长理论的推广，准确地考虑了聚合物-气体混合物的各种性质，定性地表达了工艺条件与细胞结构的关系。

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.