Nonisothermal Crystallization Kinetics of High-Density Polyethylene/Barium Sulfate Nanocomposites

The high-density polyethylene (HDPE)/barium sulfate (BaSO4) nanocomposites had been successfully prepared by melt-blending. Nonisothermal melt-crystallization kinetics of neat HDPE and HDPE/BaSO4 nanocomposites was investigated with differential scanning calorimetry under different cooling rates. The nonisothermal crystallization behavior was analyzed by Ozawa, Avrami, and combined Ozawa-Avrami methods. It was found that the Ozawa method failed to describe the nonisothermal crystallization behavior of neat HDPE and HDPE/BaSO4 nanocomposites. The modified Avrami method by Jeziorny was only valid for describing the middle stage of crystallization but was not able to describe the later stage of neat HDPE and HDPE/BaSO4 nanocomposites crystallization. The value of Avrami exponent n for neat HDPE ranged from 3.3 to 5.7 and for HDPE/BaSO4 nanocomposites ranged from 1.8 to 2.5. It is postulated that the values of n close to 3 are caused by spherulitic crystal growth with heterogeneous nucleation, whereas simultaneous occurrence of spherulitic and lamellar crystal growth with heterogeneous nucleation account for lower values of n. The combined Ozawa-Avrami method by Mo and coworkers (Polym. Eng. Sci., 37(3), 568 (1997)) was able to satisfactorily describe the crystallization behavior of neat HDPE and HDPE/BaSO4 nanocomposites. In addition, the activation energy of nonisothermal crystallization was determined using the Kissinger (J. Res. Nath Bur Stand, 57(4), 217 (1956)) method, showing that the crystallization activation energy of HDPE/BaSO4 nanocomposites was lower than that of neat HDPE. POLYM. ENG. SCI., 49:2342-2349, 2009. (C) 2009 Society of Plastics Engineers