การผลิตโฟมยางธรรมชาติโดยใช้ไมโครบับเบิลด้วยก๊าซไนโตรเจน

Abstract

Natural rubber latex foams are commonly produced by the two well-known methods of Dunlop and Talalay. Talalay foams are better flexibility and physical properties than Dunlop foams. This is due to the fact that Talalay method offers the foam with a microstructure of spherical cell shape and interconnected network structure throughout the foam while Dunlop process gives the foam with irregular cell shape and partially interconnected network structure. Recently, an alternative method using air microbubbles has been presented to simply fabricate a natural rubber latex foam with a microstructure similar to that of the Talalay foam without the need of vacuum and low processing temperature. In this research, natural rubber latex foams were fabricated using nitrogen microbubbles to study its effect on microstructure and physical properties of the foams in comparison with those of the foams produced by air microbubbles. By flowing nitrogen gas through a diffuser having a pore size range of 10-16 μm which is firmly connected to a bubble column containing compound latex, a high volume of microbubbles was generated. The flow rate used here were varied: 30, 50 and 80 mumin. The findings show that microstructure and physical properties of the foams produced by nitrogen microbbbles were significantly affected by the flow rate. Cell size increased with the increased flow rate leading to a decrease in foam density. Furthermore, compression set percentage of the foam decreased with the decreased nitrogen gas flow rate showing the better flexibility of the foam at low flow rate. In addition, the indentation hardness index values of all nitrogen foams produced from all the three flow rates were in between 101-170 N which were classified as a medium hardness. When the nitrogen foam produced at the flow rate of 50 ml/min was compared to the air foam fabricated at the identical flow rate. It was found that the foams exhibited a similar in spherical-like cell shape with interconnected network structure but different cell sizes. The air foam was found to be larger cell size that the other foam resulting in a difference in physical properties of the foams produced from different gas types. Besides, flammability test of the two foam types was compared. The results show that flammability of both the nitrogen and air foams were similar due to the fact of open cell structure of the foams. In conclusion, natural rubber latex foams could be effectively produced via nitrogen or air microbubbles. The foam produced by this microbubble technique possessed spherical cell shape with interconnected network structure. Different gas type used results in different cell size of the foam. Their physical properties could be simply altered by the adjustment of flow rate or gas type.