ObjectiveCork is a kind of natural polymer material with viscoelasticity. Cork products are mostly formed by hot pressing of cork particles after sizing except natural cork stoppers. The melting temperature, glass transition temperature and other thermal transition temperatures of the main chemical components of cork materials have important theoretical reference value for understanding the viscoelasticity of cork and formulating thermal processing technology.

MethodFirstly, the thermogravimetric analysis of the Quercus variabilis cork was carried out to determine the pyrolysis initiation temperature. Then, three thermal analysis methods, DSC, DMA and TMA, were used to analyze the thermal effect temperature of the domestic Quercus variabilis cork material within the pyrolysis initiation temperature and verify each other.

ResultThermogravimetric analysis showed that the Quercus variabilis cork did not undergo thermal degradation before 219℃. The melting temperatures of suberin's microcrystalline phases measured by DSC, DMA and TMA were 66℃, 78℃ (1Hz) and 78℃, respectively. The glass transition temperature of the amorphous region of suberin measured by DMA was about 0.7℃, and there was a secondary relaxation transition near -66℃. Each thermal effect temperature was slightly different from that of Quercus suber cork, which was related to the difference in monomer composition and intermolecular force of the chemical components of the two species cork. In addition, due to the corrugations on the radial wall of the cork cell, it was found that the thermal expansion of the cork radial dimension was greater than that of the axial direction under the heating condition.

ConclusionIn the temperature range before the pyrolysis of Quercus variabilis cork, suberin, the main component of the cork, will undergo different thermal effects, according to which the appropriate cork hot processing temperature can be determined, and the thermoforming of the cork material can be promoted by increasing the viscous flow of the cork.