Abstract
The influence of maleated polypropylene (MAPP) on the non-isothermal crystallization behavior of wood fiber (WF)-reinforced PP composites (WPCs) was investigated by a differential scanning calorimeter (DSC). The results showed that MAPP as a nucleation agent accelerated the crystallization rate of the PP matrix in WPC under the cooling process. The corresponding crystallization kinetics and activation energy were further analyzed using the Avrami method, Avrami–Ozawa method, Kissinger method, and Friedman method. The results demonstrated that MAPP significantly changed the crystal growth mechanism of the PP matrix to heterogeneous nucleation for acicular and tabular crystal growth during the annealing step. A remarkably lower cooling rate can achieve a certain relative crystallinity degree at the unit crystallization time for WPC with 3 wt % MAPP (WPCM3). Similarly, the lowest crystallization activation energy was observed for the WPCM3 among all WPCs by the Kissinger method. Furthermore, based on the Friedman method, the addition of MAPP easily caused the PP matrix to crystallize in the WPC at the initial stage of relative crystallinity.
Highlights
Over the last decade, wood fiber (WF)-reinforced polymer matrices, consisting of petroleum-based and renewable resources, have gained interest for the manufacture of products in a number of fields, such as fencing, decking, and automotive components, due to sustainability, relatively high strength and stiffness, low maintenance and cost, and good durability [1,2,3,4,5]
The non-isothermal crystallization kinetics of wood–plastic composites (WPCs) with various maleated polypropylene (MAPP) concentrations were determined by differential scanning calorimeter (DSC) and analyzed by the Avrami method, Avrami–Ozawa method, Kissinger method, and Friedman method
The Kissinger method indicated that the crystallization activation energy (∆E) decreased when WFs and MAPP were added to the PP matrix, and the WPCM3 exhibited the lowest ∆E value among all WPCs
Summary
Wood fiber (WF)-reinforced polymer matrices, consisting of petroleum-based and renewable resources, have gained interest for the manufacture of products in a number of fields, such as fencing, decking, and automotive components, due to sustainability, relatively high strength and stiffness, low maintenance and cost, and good durability [1,2,3,4,5]. The incompatibility between hydrophilic lignocellulosics and hydrophobic thermoplastics has been found to limit the applicability of wood–plastic composites (WPCs). This deficiency produces insufficient interfacial adhesion, which may lead to moisture intrusion and biological attack [6,7]; in addition, this incompatibility results in decreased mechanical properties due to poor stress transition from the matrix to the fibers [8,9]. To enhance the interfacial adhesion and to improve the properties of the composites, many physical and chemical approaches, such as the addition of coupling agents [8,9,10,11,12], silane treatment [10,13,14], alkaline treatment [13,15,16], esterification [15,17], and heat treatment [18,19], have been used. Copolymers containing maleic anhydride, such as maleated polypropylene (MAPP), Polymers 2018, 10, 382; doi:10.3390/polym10040382 www.mdpi.com/journal/polymers
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