Abstract
Researches on thermoplastic composites using natural fiber as reinforcement are increasing, but studies of durability over time are scarce. In this sense the objective of this study is to evaluate changes in the properties of polypropylene/bamboo fiber (PP/BF) composite and the influence of the use of coupling agent (CA) in these composites after natural ageing. The PP/BF (70/30 wt) composites and 3% wt CA (citric acid from natural origin and maleic anhydride grafted polypropylene from petrochemical origin) were prepared by using an internal mixer chamber and then injection-molded. The samples were exposed to natural weathering for a total period of 12 months and characterized before and after exposure. All exposed composites experienced a decrease in their properties, however, the use of CA promoted more stability; in mechanical properties, the composites with CA showed lower loss about 23% in Young′s modulus, 18% in tensile stress at break, and 6% in impact strength. This behavior was similar in thermal and physical properties, the result for the CA of natural origin being similar to that of synthetic origin. These results indicate that the use of a CA may promote higher interaction between the fiber and the polymer. In addition, the CAs of organic origin and synthetic origin exhibited similar responses to natural ageing.
Highlights
Interest in obtaining composite materials reinforced with fibers from renewable sources, lignocellulosic fibers, has grown in recent years
The materials used in this study were PP with melt flow index (MFI) 45 g/10 min (230 ◦ C/2,16Kg), manufactured by the company Braskem (Porto Alegre, RS, Brazil); polypropylene grafted with maleic anhydride (MA), (PolyBond®3200, Addivant-molecular weight of 42000 g/mol and acid number of 11 mg KOH/g) was provided by Clariant; citric acid, CI, manufactured by the company Neon Comercial Ltda (Suzano, SP, Brazil); and bamboo fiber (BF) from the Guadua angustifólia species, with particle sizes of 250 μm, from residues generated in the industrialization of bamboo (Popayán, coupling agent (CA), Colombia)
The PP is known as non-biodegradable polymer, but is sensitive a series of thermala and photophoto-oxidative reactions, that affect the performance of the materialtooccur weathering, process in oxidative reactions, that affect the performance of the material occur weathering, a process in which the incidence of ultraviolet radiation and atmospheric oxygen interact, which was confirmed in this study after natural aging
Summary
Interest in obtaining composite materials reinforced with fibers from renewable sources, lignocellulosic fibers, has grown in recent years. Lignocellulosic fibers are added to polymers to obtain composites; when used as reinforcing agents they impart certain benefits such as low density, high specific strength, and high modulus [1] This type of composites is known as wood plastic compounds (WPCs), which have a great potential in application as a new wood substitute [2]; they offer advantages in relation to insect attacks, water absorption, and degradation. Its malleability allows obtaining products of varied shapes, and easy reproduction of building elements These composites offer applications in different industries such as automotive components, construction applications, footwear, interior and street furniture, among others. Advances in this field have allowed the term to be applied to Polymers 2020, 12, 929; doi:10.3390/polym12040929 www.mdpi.com/journal/polymers
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