PLA薄膜挤出吹塑成型加工过程中温度场的研究

Temperature distributions in blown film process of PLA

对聚乳酸(PLA)在挤出吹塑薄膜成型冷却过程中的温度场进行研究,提出合理的假设,根据能量守恒定律,建立了吹膜冷却过程中膜厚方向(径向)和机器方向(轴向)的温度场分布模型。采用有限差分法,用Matlab数学软件模拟了PLA在吹膜冷却过程中的一维温度场。结果表明:在口模出口附近,PLA薄膜内外表面存在明显的温度差异,故在吹膜冷却过程中,膜厚方向的热传导必须给予考虑,只有在冻结线附近才可以忽略不计;由于空气对流传热和辐射传热在薄膜外表面进行,因此,吹膜过程的传热主要发生在薄膜外表面;冷空气流量对冻结线高度(FLH)有重要影响,通过模型计算,可以控制FLH,从而实现对薄膜性能和产量的调控。

The temperature distributions of PLA both in the thickness direction and machine direction during blown film process can be obtained with the reasonable model assumption and law of conservation of energy. FDM coupled with the CV method was applied to solve the mathematical model. MATLAB was used to simulate the one-dimensional model of temperature profiles. The results indicated that during the film blowing of PLA, significant temperature differences may ex- ist between the internal surface and external surfaces in the vicinity to the die lip, the differences gradually and eventually become negligible close to the frost line; The heat transfer of blown film process occured mainly in the film external sur- face. The cooling efficiency was critically sensitive to varying airflow rates greatly affected the freeze line height.