Karakteristik Mekanik dan Beban Hambatan (Drag Force) Komposit Polietilena Densitas Tinggi (HDPE) dengan Pengisi Abu Boiler Pabrik Kelapa Sawit (ABPKS) sebagai Material Pipa Air Laut Dingin (PALD) pada Sistem Ocean Thermal Energy Coversion (OTEC)

Abstract

Ocean Thermal Energy Conversion (OTEC) Power Plant used working fluids (ammonia) which were evaporated by warm sea surface water to produce effective pressure for electric generator. Cold sea water pipe (CSWP) was used to transport cold sea water from sea bed to the sea surface, (for 2 MW generators, require minimum 500 m depth, and 4 m diameter to reach 5oC cold sea water temperature), to condensate and circulate the ammonia vapour to produce sustainable and environment friendly electricity. Glassfibre-high density polyethylene (GF-HDPE) composites have been recommended as alternative materials for the CSWP installation. However, delicate manufacture should be carried out to achieve compatibility and finely distribution of the fiberglass, whereas the composite materials should be able to withstand against contiuous loads from sea wave and currents as well as hydrostatic pressure in deep sea environment. Palm oil mill boiler ash (POMBA) contains silica upto 17% and can be utilized as fillers and reinforcements for polymer composites. Addition of adhesion promotor (carrier) of maleated polypropylene (PPgMA), improve distribution, compatibility, and adhesion of the POMBA fillers, without formation of micropores (voids), which susceptible to crack initiation under external loads in the HDPE composites. In this works, POMBA samples were treated in acid solution, in which 32.78% of the mineral contents was washed leaving chemical composition of the ABPKS filler: Si (IV), Ti (VI), C (IV) and Oxygen. Mean/Median particle size of the treated- POMBA were smaller than those of before washing, with morphology of spherical shape without minerals coating. Then, composite materials based on HDPE with POMBA as filler in the presence of PPgMA as adhesion promiter were prepared using Twin Screw Extruder at various temperaturs (150o -180oC), and rotation speeds (60-100 rpm). It was found that the presence of PPgMA as compatibiliser, improved adhesion/interaction which inturn increased mechanical strength of the composite materials. Here, optimum composition of HDPE/PPgMA/POMBA30 composite was chosen, i.e. when POMBA loading was 30 php (per hundred polymers), and weight ratio HDPE/PPgMA: 9/1. The presence of POMBA fillers function as: reinforcements, thermal stabilizers, crystalinity reducers of the HDPE composites. Simulation of von Mises drag force due to constant wave and sea currents based-on those of in Makasar Strait in Sulawesi Selatan, using HDPE/PPgMA/POMBA composite as construction material found that structure of cold sea water pipe (CSWP) were safe if the thickness ≥ 14 cm, whereas for fluctuated wave and sea current the safe thickness ≥ 24 cm.