ABSTRACT
It is difficult to obtain suitable fire resistance and mechanical properties for glass-fiber-reinforced polymer (GFRP) roof material in industrial applications. Although some efforts to improve the fire resistance properties of GFRP have been carried out, in practice this sometimes degrades the mechanical properties. Therefore, the base materials, such as filler and reinforcing fiber, must be appropriately combined to simultaneously improve both fire resistance and mechanical properties. The present study examines improvements in GFRP roof material by investigating the effect of aluminium trihydrate (ATH) as a filler and the combination of a chopped strand mat (CSM) with woven roving (WR) and stitched mat (STM) fibers as the reinforcement in a composite GFRP roof structure. The roof samples were prepared following industrial machine standards using the specified materials. The mechanical properties of GFRP were evaluated using tensile, flexural and impact tests, following ASTM D638, ASTM D790 and ASTM D256 standards, respectively. The fire properties were examined through fire tests following the ASTM D635 standard. The results show that the GFRP roof composed of CSM/WR fibers had a 40% higher tensile strength (103.5 MPa) compared with the GFRP roof without CSM fibers (73.8 MPa). The flexural strength of the GFRP roof with CSM/WR fibers was also 57% higher than the roof without fibers, with a ratio of 315.61 MPa to 201 MPa. With the use of CSM/WR fibers, the fire resistance also increased by 23%, resulting in a ratio of 4.31 mm/min to 5.32 mm/min. These results demonstrate that the combination of CSM/WR fibers as a reinforcement would be an excellent option for producing an improved GFRP roof with better industrial properties, especially when producing improved GFRP roofs using a continuous lamination machine.
ABSTRACT
In this research, a low molecular weight poly(lactic acid) (or PLA) synthesized from direct polycondensation was melt compounded with urea to formulate slow-release fertilizer (SRF). We studied the influence of the molecular weight (MW) of PLA as a matrix and the urea composition of SRF towards release kinetics in water at 30 °C. The physical appearance of solid samples, the change in urea concentration, and acidity (pH) of water were monitored periodically during the release test. Three studied empirical models exhibited that diffusion within the matrix dominated the urea release process, especially when the release level was less than 60%. Thus, a lower MW of PLA and a higher urea content of SRF showed a faster release rate. For the entire length of the release experiment, a combination of diffusion and degradation mechanisms exhibited the best agreement with the experimental data. The hydrolytic degradation of PLA may begin after 96 h of immersion (around 60% release level), followed by the appearance of some micro-holes and cracks on the surface of the SRF samples. Generally, this research revealed the good release performance of urea without residues that damage the soil structure and nutrient balance.
