Nonisothermal crystallization of high density polyethylene and nanoscale calcium carbonate composites

Abstract

Nonisothermal crystallization of high density polyethylene (HDPE)/maleic anhydride-modified HDPE(manPE)/ nanoscale calcium carbonate (CaCO 3 ) nanocomposite was investigated by means of wide angle X-ray diffraction (WAXD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC). WAXD indicated that the crystallinity was reduced with the addition of CaCO 3 . The spherulite size of HDPE increased in the presence of manPE, but decreased when CaCO 3 was added from observation of POM. A modified Avrami analysis, Ozawa analysis, and Liu analysis were applied to the nonisothermal crystallization process. Crystallizability followed the order: HDPE/manPE/ CaCO 3 > HDPE/CaCO 3 > HDPE/manPE > HDPE when undercooling was taken into account. Dependence of the effective activation energy on the relative crystallinity was estimated by the Friedman equation, and the results were used to calculate the parameters (K g and U*) of Lauritzen-Hoffman's equation by Vyazovkin's method. These results indicate that the addition of maleic anhydride groups and CaCO 3 tend to promote the nucleation of spherulites on their surfaces and lead to epitaxial growth of the crystallites. But at the same time, manPE and CaCO 3 particles may hinder the transport of the molecule chains resulting in a decrease of the crystallization growth rate. POLYM. ENG.

Nucleating agents for high-density polyethylene-A review

“…Eder and Wlochowicz showed that the Ozawa method did not produce straight lines in the log[−log(1 − X t )] versus log R plot for HDPE indicating that this model was not adequate, which was also confirmed by Liu et al . Likewise, attempts to utilize the Ozawa method in the SiO 2 and CaCO 3 NA systems showed unacceptable nonlinear behavior in both the neat HDPE and composites during both primary and secondary crystallization phases . In all cases, this discrepancy was attributed to factors neglected in the Ozawa theory including secondary crystallization and dependence of lamellar thickness on the T c .…”

“…The constant is an empirical pre‐exponential factor. Plots of dX t / dt versus 1/ T yield a straight line with slope equal to –Δ E / R .…”

“…The parameter F ( T ) is the heating or cooling rate: and a is the ratio of the Avrami exponent n to the Ozawa exponent m or a = n / m . Mo's method was successful in describing the nonisothermal kinetics at both lower and higher degrees of crystallinity ( X > 0.8) for TiO 2 , SiO 2 , and CaCO 3 and overall a better linear fit was obtained in comparison to the Jeziorny and Avrami methods .…”

“…Those studies of NAs in HDPE that include the effect of concentration show that the performance of the NA is concentration dependent. For example, studies of NAs listed in Table , including UHMWPE , CaCO 3 , TiO 2 , SiO 2 , BaSO 4 , POSS , graphite , MWNT , and ionomer‐treated sisal fibers , correlate performance with the amount of the NA in the HDPE. It is therefore presumed that concentration‐dependent behavior is the norm rather than the exception.…”

Non-isothermal crystallization kinetics of partially miscible ethylene-vinyl acetate copolymer/low density polyethylene blends

“…Mo's method [11,12,[28][29][30] is another efficient approach derived from the combination of both Avrami equation and Ozawa model [10], which have been successfully utilized in various cases [29,31,32]. Dividing the Avrami equation by the Ozawa's equation, functions are given in Equations (7) and (8): …”