Study On Preparation Technology And Related Properties Of TPU Foamed Film

Thermoplastic polyurethane has excellent physical and mechanical properties, such as high wear-resisting, corrosion-resistance and high tensile strength,etc. The foamed material made by TPU has not only the common characteristics of TPU, but also the characteristics of the foamed material, such as portability, heat-insulation, sound-insulation, and corrosion-resistance. Foamed film has a good prospect in the application of new type of artificial leather and cushioning material. At present, the bubbles in the TPU foamed film are not even and fine enough, and the dendities of most of them are not less than 0.8g/cm3.There are also some defects in the foamed film preparing process.In this paper, Azodicarbonamide was used to blend with 1# TPU by a double-screw extruder and to foam when they were well mixed. The effect of AC on 1#TPU foam film’s properies was studied by changing the ratio of AC in the 1# TPU, foaming temperature and foaming time in the foaming process. To optimize processing conditions, the bubble average diameter, the number of bubbles, the foaming rate, apparent density, and tensile strength of the samples were compared. The results showed that the foaming effect was satisfied when the mass radio of AC to 1#TPU was 1:30, the foaming temperature 215℃, the foaming time 4min, while the bubble average diameter was 232um, the apparent density 0.35g/cm3, and the tensile strength was 2.8 MPa, declined by 30%. In addition, the rheological properties of 1#TPU was tested, and the performance during foaming procedure was analyzed based on it’s rheological properties.The AC blowing agent decomposition temperature of was relatively higher to the low hardness TPU; In order to reduce the blowing agent’decomposition temperature, urea, sodium bicarbonate and organic zinc salt were added into AC blowing agent separately or simultaneous modified compound blowing agent. The influence of the additives on the decomposition of AC blowing agent were analzed by comparing initial decomposition temperature, burst decomposition temperature and the rate of gas evlution of the modified compound blowing agents from the displacement method and TG analysis. Some conclusions were got, first of all, AC decomposition process was changed by urea and the decomposition temperature and the rate of gas evlution were reduced and the effect was optimal when the mass radio of AC to urea was 1:0.8. Second, sodium bicarbonate reduced the decomposition temperature of AC and increased the rate of gas, the effect was optimal when the mass radio of AC to sodium bicarbonate was 1:0.3. The organic Zinc salt promoted the decomposition process of AC, and the effect was optimal when the ratio of AC to organic Zinc salt was 1:0.2. Finally the ratio of compound AC of AC:urea:sodium bicarbonate:organic zinc salt was 1:0.8:0.3:0.2, the decomposition temperature of the blowing agent decreased from 205℃ to 155℃, the burst temperature range from 215～225℃ to 165～185℃, and the rate of gas evolution increased from 160ml/g to 175ml/g.According to the influence of urea on the blowing agents, the compound blowing agent Ⅰ and Ⅱ were prepared and used in different TPUs. Through the analysis of the DSC and melt index of the TPUs, the processing performance was well studied.In addition, the TG of the compound foaming agent Ⅰ and Ⅱ were analysised, the decomposing procedure of the compound blowing agent Ⅰ was more moderate, the decomposing rate was slow and the samples with uniform bubble were produced easily. Conpared the foamed samples, the compound blowing agent Ⅰ and Ⅱ,the foamed samples of the compound foaming agent Ⅰ were better, their bubble were more fine, the tensile strength was higher.And compared the foamed 2# sample was the best one, the bubble diameter was 142um, the apparent density 0.7g/cm3,the tensile strength 1.3MPa, declined by 40%. The best foaming process was that the mass radio of 2#TPU to compound blowing agent Ⅰ was 32:1, the foaming temperature 185℃ and the foaming time 1min.Through plant-size screw producing extruder, the stability and the reproducibility of the processmention alone was so good. The bubble diameter was 140μm, the apparent density 0.69g/cm3, and the tensile strength 1.33MPa, which declined by 36%.