Phase Change Materials (PCMs) are a unique ingredient in the Vacuum Insulation Panel (VIP) core to improve its thermal mass. The integrated PCM in VIP core is exposed to a pressure below 1 mbar, so its phase transition behaviour needs to be investigated in the vacuum environment. Phase transition effect of three types of Shape Stable Phase Change Material (SSPCM) during charging-discharging in ambient pressure and 0.4 mbar pressure was analysed in this work. Neopentyl Glycol (NPG), Polyurethane (PU) and Microencapsulated Paraffin (MEP) were used as the SSPCMs in this study. Temperature-time (T-t) plot and the mass loss of the three SSPCM during its charging-discharging period in both pressure conditions were analysed. Structural, morphological, chemical and thermophysical properties differences of SSPCM after charging-discharging cycles in both pressure conditions were analysed separately. From XRD analysis, the structural stability was observed with slight percentage changes in crystallinity. DSC analysis reveals more phase transition reversibility and low subcooling effect for samples from vacuum condition. PU and NPG experienced an increase in thermal diffusivity after vacuum thermal cycle. T-t plot analysis was effective for the analysis of phase transition behaviour of bulk SSPCM during charging-discharging in different pressure. The difference in phase transition behaviour in both pressure conditions was analysed. MEP recorded the least mass loss of 0.78% and 0.82% in both pressure conditions while NPG at vacuum showed the highest mass loss of 8.45%. The results show that MEP was comparatively better SSPCM for integration in VIP.

相变材料（PCM）是真空绝热板（VIP）芯中的一种独特成分，可提高其热质量。VIP芯中集成的PCM承受的压力低于1 mbar，因此需要在真空环境中研究其相变行为。这项工作分析了三种类型的形状稳定相变材料（SSPCM）在环境压力和0.4 mbar压力下充放电期间的相变效应。在这项研究中，新戊二醇（NPG），聚氨酯（PU）和微囊石蜡（MEP）被用作SSPCM。分析了两种压力条件下三个SSPCM在充放电期间的温度-时间（Tt）图和质量损失。结构，形态 分别分析了两种压力条件下充放电循环后SSPCM的化学和热物理性质差异。通过XRD分析，观察到结构稳定性，并且结晶度有微小百分比变化。DSC分析显示，真空条件下的样品具有更高的相变可逆性和较低的过冷效应。真空热循环后，PU和NPG的热扩散率增加。Tt图分析对于分析大体积SSPCM在不同压力下充放电过程中的相变行为是有效的。分析了两种压力条件下的相变行为差异。在两种压力条件下，MEP的质量损失最低，分别为0.78％和0.82％，而真空中的NPG的最高质量损失为8.45％。