Hybrid Composites from Wheat Straw, Inorganic Filler, and Recycled Polypropylene: Morphology and Mechanical and Thermal Expansion Performance

Abstract

Reinforcing effect of hybrid filler including wheat straw (WS) and inorganic filler (heavy calcium carbonate, silicon dioxide, and fly ash) in recycled polypropylene (R-PP) has been investigated. The effects of individual filler (WS) and combined fillers (WS and inorganic filler) on morphological, mechanical, and thermal expansion and water absorption properties of hybrid composites were investigated. The flexural modulus and flexural strength were both reduced when reinforced with three kinds of inorganic fillers, respectively, which was possibly due to the poor interphase adhesion as observed in SEM. The high surface energy of heavy calcium carbonate due to its high acidic character provides an opportunity of better PP-heavy calcium carbonate interfacial interactions compared to PP-straw, PP-fly ash, and PP-SiO 2 interface. The water absorption at saturation increased markedly by introduction of WS in it. The hybrid composites from WS and inorganic fillers showed better water absorption compared to those WS/PP composites. The thermal expansion of composites decreased with the increase of WS loading. Heavy calcium and SiO 2 can obviously reduce the LCTE value of composite. At the 25% inorganic filler content, composites had the smallest LCTE values.

Thermoplastic/Natural Filler Composites: A Short Review

“…Indeed, many applications have been paying attention on the use of natural polymers which are inexpensive, renewable and also biodegradable. [35][36][37] Efforts are ongoing to determine unconventional resources for biopolymers. Corn stover, wheat straw and cotton stalk, soy protein as well as wheat gluten are among the agricultural by products and agricultural coproducts that have been explored for their potential use as a matrix.…”

Properties and Morphology of Polypropylene/Big Bags Compounds

“…These three oxides represent more than 95% of the mineral fillers added to virgin PP during big bags processing to obtain the fabrics of big bags. These additives may act as pigments providing white color (CaO), ultraviolet resistance (anti-uv) (TiO 2 ), nucleation, among other properties, probably they behave as external agents during recycling of R BB implying in changes in virgin PP [18][19] .…”

“…Decomposition temperatures are possibly associated to the difference in the viscosity between PPs, where PP H503 being more viscous has a higher molecular weight and consequently greater macromolecular entanglements, leading to a higher energy consumption to break the chains, therefore to higher degradation/decomposition temperatures as already observed by Rjeb et al (2005) 20 . The plot for R BB displays weight loss in higher temperature than those observed for PP H103 and PP H503 what can be attributed to the mineral fillers/ additives as evidenced by FRX analysis [18][19] . Figure 2 presents TG plots of PP compounds with 10, 30 and 50% of R BB .…”

“…Melting endotherms related to fusion of crystals are observed during heating, in Figure 3a. The melting peak of R BB is displayed at relatively higher temperatures, possibly due to the formation of larger and/or more stable crystals due to the stretching during processing leading to a greater orientation or even due to the presence of mineral fillers as evidenced in Table 2 12,18,19 .…”

“…Regarding Tensile Strength, investigated compounds display similar values, while PP H503 presented higher Impact Strength, on average data were 30% higher than compounds with PP H103. In general, addition of R BB leaded to an improvement of impact, possibly mineral fillers provide better energy absorption 18,19,11 . The results obtained with tensile and impact experiments give evidence that addition of R BB to neat PP provide compounds with higher performance at lower cost.…”