Cold seawater pipes (PALD) in Ocean Thermal Energy Conversion (OTEC) power plants function to channel deep seawater to the surface power generation system. For a 100 MW power plant, a depth of more than 500 m with a pipe diameter of 4 m and cold seawater temperature of 5°C is required. In this system, the working fluid (ammonia) is evaporated by surface seawater with a minimum temperature of 25°C, producing vapor pressure and electricity, and then recondensed by the cold seawater. This produces a sustainable and environmentally friendly power generation system without fossil fuels. However, the materials for PALD installation must withstand wave loads, fatigue, and hydrostatic pressure from deep-sea currents.

High density polyethylene/fiberglass (HDPE/fiberglass) composites have been used as PALD materials because they are cheaper, insulating, and corrosion resistant. However, during the hot blending manufacturing process, fiberglass fillers are poorly distributed, prone to breakage, and reduce mechanical strength. Palm oil mill boiler ash (ABPKS) contains up to 17% silica particles that can serve as fillers and reinforcements for HDPE composites. With the aid of a maleic anhydride derivative compatibilizer (PPgAM), fillers are distributed more evenly and free of microvoids. The addition of styrene butadiene rubber (SBR) also enhances the impact resistance of HDPE/SBR blends after vulcanization with sulfur cross-linking agents.

In this study, HDPE/SBR composites were prepared with ABPKS filler, PPgAM compatibilizer, and sulfur vulcanization additive using an internal mixer and twin screw extruder under optimum conditions (Taguchi optimization method). The resulting HDPE/SBR/PPgAM/ABPKS composites were tested for physicochemical properties including density, thermal conductivity, optical properties, FTIR spectroscopy, filler particle diffusion, and contact angle. Composite characteristics were also investigated through rheological tests (rotational rheometer and melt flow index), mechanical properties (tensile strength and elongation according to ASTM), hardness (Rockwell), fracture surface morphology with SEM/EDX, X-ray diffraction (XRD/XRF), and thermal properties (TGA/DSC). Extrusion results showed that HDPE/SBR blends mixed uniformly, and the addition of ABPKS increased extrusion time and repeatability with increasing ABPKS mass.

Mechanical and thermal test results showed that HDPE/SBR composites with ABPKS filler had increased tensile strength from 14.06 MPa to 16.936 MPa. Thermal analysis revealed decomposition at 518.65°C with a total mass loss of 81.01%. SEM analysis confirmed homogeneous mixing of HDPE/SBR/PP-g-AM with ABPKS filler, indicating strong interactions between the HDPE/SBR/PP-g-AM matrix and ABPKS.