New Composites Derived from the Natural Fiber Polymers of Discarded Date Palm Surface and Pineapple Leaf Fibers for Thermal Insulation and Sound Absorption.

New composites made of natural fiber polymers such as wasted date palm surface fiber (DPSF) and pineapple leaf fibers (PALFs) are developed in an attempt to lower the environmental impact worldwide and, at the same time, produce eco-friendly insulation materials. Composite samples of different compositions are obtained using wood adhesive as a binder. Seven samples are prepared: two for the loose natural polymers of PALF and DPSF, two for the composites bound by single materials of PALF and DPSF using wood adhesive as a binder, and three composites of both materials and the binder with different compositions. Sound absorption coefficients (SACs) are obtained for bound and hybrid composite samples for a wide range of frequencies. Flexural moment tests are determined for these composites. A thermogravimetric analysis test (TGA) and the moisture content are obtained for the natural polymers and composites. The results show that the average range of thermal conductivity coefficient is 0.042-0.06 W/(m K), 0.052-0.075 W/(m K), and 0.054-0.07 W/(m K) for the loose fiber polymers, bound composites, and hybrid composites, respectively. The bound composites of DPSF have a very good sound absorption coefficient (>0.5) for almost all frequencies greater than 300 Hz, followed by the hybrid composite ones for frequencies greater than 1000 Hz (SAC > 0.5). The loose fiber polymers of PALF are thermally stable up to 218 °C. Most bound and hybrid composites have a good flexure modulus (6.47-64.16 MPa) and flexure stress (0.43-1.67 Mpa). The loose fiber polymers and bound and hybrid composites have a low moisture content below 4%. These characteristics of the newly developed sustainable and biodegradable fiber polymers and their composites are considered promising thermal insulation and sound absorption materials in replacing synthetic and petrochemical insulation materials in buildings and other engineering applications.