Modified polypropylene wood flour composites. II. Fracture, deformation, and mechanical properties

Abstract

ABSTRACT:The effect of grafting level of maleic anhydride (MA) in the maleated polypropylene (PPMA) on the fracture, deformation mechanisms, and mechanical properties of polypropylene (PP) wood flour composites was studied. Tensile strength, elongation at break, and impact strength are noticeably improved with addition of interfacial modifiers as maximum values of the examined mechanical properties were detected when concentration of MA in the compatibilizer was 1 wt %. To explore the microstructure and deformation mechanisms, scanning electron microscopy was employed. It was found that low concentrations of MA up to 1 wt % led to the creation of a thin and irregular polymer layer assisted formation of fibrillated plastic deformation zone around the wood particles, while the bulk PP matrix experienced voiding and brittle fracture. Higher concentrations of MA fetch to stronger interaction between PP and wood flour, the reason for brittle fracture and reduced ductility of the matrix. The impact fracture behavior of the composites during Instrumented impact tests is also discussed with respect to the interfacial bond strength.

Wood flour filled PP composites: Compatibilization and adhesion

“…The orientation, orientation distribution and possible aggregation of wood particles all add to the structural variety of such composites. Finally, interfacial adhesion is determined by the presence or absence of MAPP, but also by its functionality, since larger maleic ahydride content was claimed to lead to stronger interaction and decreased impact resistance [25]. It is impossible to consider all these factors in one paper, thus although we mention most of them, we focus our attention on composition, interaction and MAPP properties.…”

“…The maleinated PP with the larger functionality and smaller molecular weight improves strength only slightly, while composites containing 10 the Orevac CA 100 grade have considerably larger strength. The use of functionalized polymers with larger functionality was claimed to be more beneficial in PP/wood composites before, based on the reasoning that larger number of MA groups would result in stronger interaction and decreased impact resistance [2,25]. One may wonder here about the definition of the strength of interaction, though.…”

“…Decreased impact strength of PP/wood composites was explained with the stronger interfacial adhesion and rigidity created by the larger functionality of MAPP used [25]. If we define the strength of adhesion by the strength of the covalent bonds formed, it must be the same for all MAPP coupling agents.…”

“…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.…”

Thermoplastic Matrix Reinforced with Natural Fibers: A Study on Interfacial Behavior

“…20. As can be seen, the addition of PP-g-MA improved E' of the composites, that was because PP-g-MA could lead to the creation of a thin and irregular polymer layer, which could assist formation of plastic deformation zone around the fiber (Hristov et al, 2004). Further, incorporation of compatibilizer to composites containing silane treated wood flour decreased tan due to the more intense filler-matrix interaction.…”