Abstract
The durability of hemp fibers reinforced polypropylene biocomposites was investigated after one year under glass exposure. Volatile organic compounds emissions were assessed using a new passive sampling method. Degradation pathways were examined in order to understand the weathering mechanisms. The polymer matrix was decomposed into oxygenated products due to UV rays and high temperatures. As regards hemp fibers, different degradation steps of the carbohydrates were highlighted according to the nature of the detected furans. At a non-weathered state, dehydrations preceded the ring-opening mechanism, often catalyzed by Maillard reactions. The further cyclization induced the formation of 2-or 5-substituted furans emitted by non-weathered materials. Reactions between identified products after weathering which were not yet found in literature were proposed in this paper. They often implied a keto-enol tautomerism but also dehydrations that induced the formation of 3-and 4-substituted furanones. These differences can be explained by a primary decomposition of carbohydrates favored at a non-weathered state and a secondary one occurring at a weathered state.
Highlights
Bio-fillers have emerged as an attractive alternative to inorganic fillers in the reinforcement of thermoplastics in response to growing awareness of environmental issues and increasing global waste problems (Liu and Hu, 2008)
Some emitted volatile organic compounds (VOCs) were issued from the polymer degradation: long-chain aliphatic hydrocarbons and oxygenated products
Radical reactions lead to intermediate tertiary alkoxy radicals and their β-scission induces the previously identified carbonyl products (Figure 2). 2,4-pentanedione can result from the oxidation of methylketone issued from polymer chain reaction with unstable hydroperoxide
Summary
Bio-fillers have emerged as an attractive alternative to inorganic fillers in the reinforcement of thermoplastics in response to growing awareness of environmental issues and increasing global waste problems (Liu and Hu, 2008). During the melt mixing process of biocomposites through extrusion and injection molding, the high manufacturing temperatures exceed the bio-fillers degradation temperature (Dorez et al, 2013; Khazaeian et al, 2015) During their use, climatic conditions weaken their chemical stability because of their high sensitivity (Zou et al, 2008; Ahmad et al, 2011; Badji et al, 2017). A press molding temperature increase induces biocomposites color turning from brown to close to black (Shibata, 2016). This was thought to be the result of vegetal fibers caramelization. Molecules responsible for the worsening air quality, color changes, and odors must be assessed
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