This study aims to investigate the effects of multi-walled carbon nanotubes (MWNTs)/linear low density polyethylene composite-coated copper sheets on an energy conversion efficiency of a solar water heating system. Volume percentages of 1, 3 and 5 MWNTs were ball-mill mixed with linear low density polyethylene before using a hot press method to coat the composites. A bonding layer between the composites and the copper sheets was intercalated using MWNTs/polyvinyl butyral composites. The strength of the bonding layer was tested using a shear tension test. Microstructures of the composites were observed by scanning electron microscopy. The energy conversion efficiency and solar absorptance of the solar heat absorbing coatings were measured by a home-made method and ultraviolet visible spectroscopy, respectively. The results showed that the efficiency and the absorptance increased by 40% and 0.95, respectively with the increasing volume percentages of MWNTs up to 5 vol.% in linear low density polyethylene.

Step-heating (single-and four-step heating) was used in the melt-mixing preparation of linear low density polyethylene (LLDPE)/multi-walled carbon nanotube (MWNT) composites. The MWNT in the composites were used at volume fractions of 0, 1, 3, 5, and 10 vol% (four-step heating), and 0, 1, 3, and 5 vol% (single-step heating). The effects of the heating steps on the microstructure of the LLDPE/MWNT composites were studied. An ultimate tensile testing machine and an impact testing machine were used to characterize the mechanical properties of the composites. The sample prepared using four-step heating had a lower porosity than the sample prepared using single-step heating. The sample with 3 vol% MWNT that was prepared using four-step heating had tensile strength, elastic modulus, and impact strength values that were higher than those of the other samples.