| Summary: | 碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 107 === Nanocellular foam and ultramicrocellular foam becomes an interesting material to be explored due to the superior properties offered. Nanofoam with low foam density in the range of 0.1-0.2 g/cm3 is a good candidate to be used as a thermal insulating material, but still challenging to be obtained. Introducing big bubbles to nanofoam can become one solution to obtain low density without losing the insulating and mechanical properties possessed by nanofoam. In this study, three grades of PMMA with different molecular weight, labeled as PMMA-L, PMMA-M, and PMMA-H were used as the raw materials. PMMA blends were prepared by blending either PMMA-L or PMMA-M with various wt% of PMMA-H, labeled as “PMMA-LH” or “PMMA-MH,” to obtain PMMA matrices with varied viscoelastic properties. The novelty of this study lies in the bimodal foam production only by blending one type of polymer with different molecular weight, thus eliminate dispersion and compatibility problems. Bimodal foams were successfully fabricated by solid-state foaming using CO2 as a blowing agent. Based on cell size analysis, the transition from ultramicrocellular to nanocellular foam can be observed in PMMA-LH blends and PMMA-MH blends at certain PMMA-H content, which is defined as the critical point. It was found that the critical points of PMMA-LH occur at the addition of 30 to 40 wt% PMMA-H, while for PMMA-MH occur at the addition of 10 to 20 wt% PMMA-H. Moreover, in those critical points, cell morphology transition from closed cell to open cell was also observed and such a result could be explained by estimating the non-entangled percentage of PMMA.
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