Prevention of Environmental Degradation of Epoxy Resins Modified with the Addition of Different Fillers

Abstract

Timber composites such as glulam beams are increasingly being used outdoors where their service life depends to a large extent on the durability of the adhesive used in the composite. Enhancing the durability of epoxy resins used in such composite materials would prolong their service life and enable them to compete more effectively with other structural materials such as concrete and steel. The weathering of timber composites is caused by a complex combination of chemical, thermal, physical and mechanical effects. This study sought to improve our understanding of the photodegradation of two epoxy resins and the relationship between timber and epoxy resin photodegradation. The effectiveness of the following fillers applied in two epoxy resins of protecting from photodegradation was investigated: functionalised multi-walled carbon nanotubes, microcrystalline cellulose, and calcium sulfate. First, the effect of accelerated weathering on the properties of two epoxy resins (hydrogenated diglycidyl ether of bisphenol A, HDGEBA, aliphatic epoxy) and (diglycidyl ether of bisphenol A, DGEBA, aromatic epoxy) was followed by exposing to accelerated weathering conditions, which are UV irradiation (UVA-240 nm), moisture, and increased temperature with different accelerated weathering times (1, 2, 3, 4, and 6 months). All samples after exposure were examined for structural and chemical changes of the epoxy resin specimens and were analysed using Fourier Transform Infrared (FTIR) spectroscopy, thermal tests, mechanical tests, and Scanning Electron Microscopy (SEM). The overall results obtained showed that epoxy composites exhibited ore resistant to reduce degradation when exposed to different accelerated weathering. The initial exposure time of one and two months did not show significant changes in the chemical, thermal, and mechanical properties of epoxy resins and epoxy composites. HDGEBA incorporated CS and MWCNT showed the highest potential to improve the resistance to increase photodegradation, which was approved by the FTIR (carbonyl and hydroxy indices), thermal (TGA and DSC), mechanical (tensile strength), and morphology tests after exposure to different accelerated weathering times. The results of chemical degradation were evaluated by using carbonyl and hydroxyl index, which indicated that HDGEBA and HDGEBA composites have lower carbonyl and hydroxyl indices after exposure to accelerated weathering with different times compared to those of DGEBA and DGEBA composites. The results of mechanical tests before and upon exposure to accelerated weathering showed that DGEBA and DGEBA composites have a higher tensile strength and lower elongation at break compared to those of HDGEBA and HDGEBA composites. However, after exposure to six months accelerated weathering, the HDGEBA and HDGEBA composites exhibited more resistance to a reduction in tensile strength compared to those of DGEBA and DGEBA epoxy composites. The tensile strength of DGEBA /2% CS and DGEBA /0.5% MWCNT composites showed higher tensile strength and less elongation at the break before exposure. However, the HDGEBA/2% CS and HDGEBA /0.5% MWCNT showed less reduction of tensile strength and higher reduce of elongation at break after the accelerated weathering (six months). The overall results of thermal tests for HDGEBA composites exhibited more resistance and improved thermal stability. The glass transition temperature (Tg) values have higher values of DGEBA samples; however, after exposure of accelerated weathering, the HDGEBA composites exhibited more resistance to decrease in the Tg values. The changes on the surface of exposed and unexposed samples were observed by using SEM and the obtained results showed that HDGEBA composites had a smooth surface before exposure while little fractures were shown on the surface after exposure and they are less effective compared to those of DGEBA and DGEBA composites. After exposure of six months, the XRD results showed that the intensity of all epoxy resins and epoxy composites were shifted in angles and reduced compared to those of corresponding samples before exposure. However, the HDGEBA composites showed higher resistance to decrease the intensity with lesser shift in theta angles than the DGEBA composites. <br/> The novelty of the work consists of the using of new epoxy resin (HDGEBA) and its composite to be compared with another epoxy (DGEBA), which are using commonly in industrial and engineering applications. Two epoxy resins evaluated different environmental conditions and are tested by utilising several analysis techniques. The results obtained of this work proved that the HDGEBA and its composites (CS and MWCNT fillers) exhibited more resistant to increase the environmental conditions and improved the chemical degradation, thermal stability, and mechanical degradation compared to that of DGEBA epoxy resin. As the results of the investigation of this work, the HDGEBA and HDGBA composites have a significant impact to be replaced the HDGEBA and HDGEBA composites for industrial application, especially epoxy coating fields.