Influence of Mercerization on the Physical and Mechanical Properties of Polymeric Composites Reinforced with Amazonian Fiber

Abstract

Natural fiber has been an attractive alternative as reinforcement in polymeric composites. However, their physical properties can be impaired due to the hydrophilic behavior of the vegetal fibers: the weak bonds at the interface fiber/matrix emerge due to the hydrophobic behavior of some polymeric matrices. This paper aims to evaluate the influence of mercerization process in Leopoldinia piassaba fibers on the physical, mechanical, thermal, morphological, and accelerated aging properties of polyurethane (PU)-based composites produced by the thermoforming process. The experimental design (22+1) was applied considering the parameters NaOH Treatment and %(PU)Resin. The NaOH Treatment consisted of 5 % and 10 % NaOH solution for fibers mercerization, and %(PU)Resin consisted of different amounts of PU (15 %, 17.5 % and 20 %). The mercerization process chemically modified the interface fiber/matrix and improved the resistance of the composite to screw withdraw strength, ranging from 573 N to 1019 N, and from 574 N to 1648 N considering Surface and Top, respectively. According to Scanning Electron Microscopy (SEM) analysis, the mercerization process also improved the fiber/matrix adherence and reduced pores, resulting in swelling decreasing and thermal conductivity increasing. Furthermore, the mean thickness swelling (TS) value ranged from 6 to 15 % and was not statistically different after accelerated aging. The developed composites containing untreated fibers showed thermal conductivity values similar to the commercial medium density fiberboard (MDF).