Mechanical Behavior of Wood/Polypropylene Composites: Effects of Fibre Treatments and Ageing Processes

Abstract

Practical applications of wood based composites are limited by the hydrophilic nature of cellulose, which causes dispersion and moisture absorption problems. This work rests on the effects of wood treatment on the mechanical properties of composites made with wood flour and polypropylene (WF/PP). Two different fiber treatments (mercerization with a 10% NaOH solution and functionalization with Epolene E-43 MAPP copolymer), their combined action, and two compounding methods have been studied. In addition, the investigation includes the analysis of the mechanical behavior of composites after exposure to variable conditions of temperature and moisture.

Wood flour filled PP composites: Compatibilization and adhesion

“…The functional groups of these polymers were shown to interact strongly or even react chemically with the surface of wood [17,24,26], while the long alkyl chains diffuse into the matrix making stress transfer possible. The stiffness of the composites is not influenced significantly by the presence of the functionalized polymer [3,17,27], but strength usually increases considerably [2,3,17,19,27,28]. The tensile and flexural strength of polymers usually decreases with increasing filler content in the absence of coupling [2,19,28,31], but the correlation can be turned around and considerable increase can be achieved with the help of functionalized polymers.…”

“…Various techniques are used or at least tried for the improvement of 4 interfacial adhesion including the treatment of the wood with sodium hydroxide [4,19,20], coupling with functional silanes [4], or the coating of wood flour with stearic acid [21,22]. However, polymers functionalized with maleic anhydride (MA) or acrylic acid (AA) are introduced the most often into polyolefin composites [2][3][4]17,[19][20][21][22][23][24][25][26][27][28][29][30]. The functional groups of these polymers were shown to interact strongly or even react chemically with the surface of wood [17,24,26], while the long alkyl chains diffuse into the matrix making stress transfer possible.…”

Influence on the Physical Properties of Wheat Straw via Hydrothermal and Chemical Treatments

“…It could also break the chemical bonds between lignin and carbohydrates, which made the lignin structures destroyed and dissolved. This would then lead to more voids on the fiber surface and rougher surface, and therefore improved adhesion (Cantero et al 2003). It also causes the contraction of the tensile section and the cellulose-bearing fiber of the wheat straw, which is why the tensile strength and elastic modulus increased (Li et al 2009).…”

“…The mechanical properties of cellulose depend on the proportion of crystalline and amorphous regions and the spiral angle of microfibrils (Cantero et al 2003). It is well known that lignin and hemicellulose are amorphous polymers.…”

“…Chemical modification of natural fibers has been widely used in the manufacture of wood polymer composites (Hristov et al 2004;Karimi et al 2006). Alkalization can eliminate a large amount of hemicellulose and other impurities of natural fibers, leading to more voids on the fiber surface and rougher surface, and therefore improved adhesion (Cantero et al 2003).…”