Study on crystallization kinetics of LDPE filled with CaCO₃ of different size and size distribution

Abstract

The thermoplastic filled with the different size distribution fillers was a new method for improving processability of thermoplastic composites. In our former study, we found that the melt torque of low-density polyethylene (LDPE) composites, which were filled with 30 wt % the effective size distribution CaCO 3 , evidently decreased. In this article, two sizes of CaCO 3 , 600 meshes and 2500 meshes, were blended by different proportions and were filled into LDPE matrix with 30 wt %. Crystal process, isothermal crystallization kinetics, and nonisothermal crystallization kinetics of a series of composites were characterized by differential scanning calorimeter (DSC). The results showed that composites filled with the effective size distribution CaCO 3 leaded to the lower melting and crystallization temperature, the more wide crystallization temperature area, while their the crystallization rate constant (k) of isothermal crystallization kinetics decreased and their Avrami exponents (n) and crystallization halflife (t 1/2 ) of isothermal crystallization kinetics increased compared with those of the composites filled with the single size CaCO 3 . Nonisothermal crystallization kinetics had the similar results.

Nonisothermal crystallization of highly‐filled polyolefin/calcium carbonate composites

“…DSC investigations were used to determine stearic acid influence on the polyolefin‐calcium carbonate composites crystallization behavior. After converting DSC crystallization curves at different cooling rates (Φ = 5, 10, 20, 30°C/min), relative crystallinity as a function of time and temperature was determined . Calculations were based on the following equations: where X t ( t ), X T ( T ), and X t (∞), X T (∞) indicated relative crystallinity at time t and temperature T and at the end of the crystallization process, whereas dH(t)/dt and dH(T)/dT were the heat flow rates.…”

“…To analyze the mechanism of crystallization at its early stage, crystallization kinetics analysis was undertaken by applying Avrami theory modified by Jeziorny . The model of crystallization that was used allowed to determine crystallization kinetics parameters during nonisothermal crystallization after an adequate correction of the crystallization rate: …”

“…After converting DSC crystallization curves at different cooling rates (U 5 5, 10, 20, 30 C/min), relative crystallinity as a function of time and temperature was determined. [29][30][31][32][33][34][35][36][37][38] Calculations were based on the following equations:…”

“…In case of highly‐filled composites (that contain between 30 and 50 wt % of the filler) designated for cast film production, the evaluation of crystallization kinetics, especially during primary crystallization, is necessary. Various papers present the application of the modified Avrami theory with regards to nonisothermal crystallization of several polymers . It should be mentioned that only few papers focused on crystallization kinetics behavior of highly‐filled composites .…”

“…Various papers present the application of the modified Avrami theory with regards to nonisothermal crystallization of several polymers. [29][30][31][32][33][34][35][36][37][38] It should be mentioned that only few papers focused on crystallization kinetics behavior of highlyfilled composites. 31,32 The main issue was the nonlinearity of Avrami crystallization curves that led to some problems with function fitting and interpretation of crystallization parameters.…”