Effect of lamellae thickness on bubble dissolution in rotomoulding

This paper is devoted to the study of bubble dissolution of the melted polymer in rotomoulding process. Two types of linear low-density polyethylene (LLDPE) having the same properties, that is, melt index, melting point, crystallinity, viscosity, comonomer type, but different lamellae thickness were investigated. The results showed that bubbles in rotomoulded parts impaired the low-temperature impact and LLDPE with thicker lamellae showed better bubble dissolution. Furthermore, as the annealing treatment was applied to the LLDPE powders, lamellae thickness distribution derived from Thomson-Gibbs equation coincided with bubble observation, suggesting that the improvement in bubble dissolution is reasonably attributable to annealing which makes the lamellae of treated LLDPE thick. In addition, the rheological measurements showed that modulus was built-up with time indicating intermediate disentanglements are formed. Correlation between lamellae thickness distribution derived from differential scanning calorimetry data and experimental rheological result suggests that thicker lamellae is related to enhancing bubble dissolution. Consequently, it is reasonable to consider that the thicker lamellae is quite benefit for bubble dissolution, which could be well explained by the free volume according to free volume theory. LLDPE having thicker lamellae contains more free volume resulting in better bubble dissolution. KEYWORDS bubble dissolution, disentanglement, lamellae thickness, rotomoulding
1 | INTRODUCTION Rotational molding, also known as rotomoulding or rotocasting, is a process for producing hollow plastic products. It involves tumbling a thermoplastic powder and heating the mold in [...]