Flexural strength and flammability of pineapple leaf fiber (PALF)/fire retardants reinforced polymer composites

Abstract

The use of natural fibers as reinforcement in composite materials, such as pineapple leaf fiber (PALF), has been extensively studied. However, it is important to note that natural fiber-reinforced polymer composites are often associated with high flammability. The aim of this paper is to investigate the mechanical properties and fire retardancy of Pineapple Leaf Fiber (PALF) reinforced polymer composites treated with various flame retardants. The PALF composites were treated with different fire-retardant additives, including ammonium polyphosphate (APP), aluminum hydroxide (ALH), and magnesium hydroxide (MH), at varying ratios (10 wt%, 20 wt%, and 30 wt%). The flexural properties of the PALF composites were assessed using a Universal Testing Machine (UTM) in accordance with ASTM D7264. The flammability testing was conducted following the Underwriters Laboratories 94 (UL-94) using standard ASTM D635 and ASTM D3801. The results of flexural tests indicated that PALF-reinforced polymer composites containing 10% MH as fire retardant exhibited the highest flexural strength (102.96 MPa). Scanning Electron Microscopy (SEM) was employed to analyze the fracture behavior of PALF-reinforced polymer composites with different fire-retardant additives. The SEM analysis revealed various characteristics including fiber pull-out, fiber breakage, inhomogeneous structural distribution (in cases of APP, MH, ALH), presence of undesired bubbles, and fiber–matrix cracking. In terms of fire retardancy, the most promising results were obtained with the addition of 20% and 30% APP. These compositions achieved V-1 and V-0 ratings respectively, in the vertical UL-94 flammability test. Notably, the horizontal test demonstrated that the composites containing 30% APP did not sustain burning and exhibited no burning rate. Similarly, the composite with 20% APP self-extinguished before the first mark without any observable burning rate.