that can be used to epoxidize fatty acids to convert the unsaturation to epoxy

 Soybean oil and linseed oil also referred to as flaxseed oil that are usually used for epoxidation to produce epoxidized linseed oil (ELO) and epoxidized soybean oil (ESO). ELO-based resin utilized as the matrix for natural fibre compos- ites has showed a flexural modulus of 1.8GPa and a strength of 60 MPa (Boquillon 2006), which are very close to the strength and flexural modulus of synthetic resins. ESO can be modified using acrylic acid and become acrylated epoxidized soybean oil (AESO) (Akesson et al. 2009), which is also used as the matrix resin in natural fibre thermoset matrix composites. In addition to that, ESO can be transformed into methacrylated soybean oil (MSO) (Ramamoorthy et al. 2012) and the MSO can also be modified to methacrylic anhydride-modified soybean oil (MMSO) using methacrylic anhydride (Adekunle et al. 2011). Bio-based epoxy resins have been proven to be environmentally friendly. However, their high water absorption and their swelling present limitations when compared to the traditional epoxy resins (Masoodi and Pillai 2012). Akesson and his colleagues reported that hemp reinforced AESO resin shows an increase in mechanical properties which can be also applied to DPF to develop sustainable biodegradable composites (Akesson et al. 2009). 144 S. Awad et al. 3.3 Thermoset Matrix Systems in Date Palm Fibre Composites Research on DPF reinforced thermoset composites are done using synthetic ther- moset polymer matrix and to date no bio-based thermoset matrix has been used for developing DPF composites. Al Kaabi and his colleagues are the first researchers who investigated the effect of different DPF loading, 6–10%, and DPF length treated with three different chemicals on the mechanical properties of the composite. Their results showed that the optimal fibre loading was 9% treated with 5% NaOH solution for 2 h. 

Where the date palm fibre reinforced composite (DPFRC) had higher flex- ural strength, flexural modulus and impact strength than the thermoset polymer by approximately 66%, 50%, 475% respectively (Al-Kaabi et al. 2005). The effect of a higher fibre loading baby shower net, 20–60%, and the fibres orientation, woven or unidirectional, on the mechanical properties of DPFRC without any prior treatment of the DPF was also reported, showing that both unidirectional and woven orientation DPF reinforced polyester resin had greater mechanical properties than neat polyester resin, however shower sponge environmentally friendly, unidirectional orientation had higher mechanical properties than the woven orienta- tion reinforced DPF, where the flexural strength and elongation increased with the increase of fibre loading. On the other hand, the impact strength decreased with the increase of DPF loading. The flexural strength and elongation of the optimum unidi- rectional orientation DPF (60% loading) reinforced polyester composites increased approximately by 55% and 10% respectively compared to neat polyester compos- ites. However, the inter-laminar failure and delamination always occurred along the fibre/matrix interface (Wazzan 2005). Using poly epoxy as a matrix with varying DPF loadings, 5%, 10%, and 15%, subjected to oxidation using soxhlent extraction, was also investigated and the results showed that there was a slight increase in flexural modulus of the reinforced composites with the increase of DPF loading by 19%, and a decrease in the stress at break or elongation and impact strength with the increase of DPF loading by 71% and 87% respectively (Sbiai et al. 2010). The effect of various diameters of DPF treated in 6% NaOH solution on the strength of reinforced epoxy composites was reported. It was found that the mechan- ical properties increased with the decrease in diameter of treated DPF. DPF with diameter size ranging from 200 to 400 μm has 120% and 13% higher tensile strength and Young’s Modulus respectively than DPF diameter size ranging between 600 and 800 μm. The elongation strain of untreated DPFRC is higher than the treated DPFRC by 65%, 77%, and 15% for DPF diameters ranging between 200 and 400, 400 and 600, and 600 and 800 μm respectively (Abdal-Hay et al. 2012). A recent investi- gation on the effect of different DPFs from different parts of DPT on epoxy matrix composites showed an increase in mechanical properties of epoxy composites bath sponge bulk, with the tensile strength, tensile modulus, flexural strength, flexural modulus and impact strength showing an increase using different types of DPTF. 

The highest increase was with the reinforcement of date palm fruit bunch stalk, having higher tensile strength, tensile modulus, flexural strength, flexural modulus and impact strength than neat Polymer Matrix Systems Used for Date Palm Composite Reinforcement 145 epoxy resin by 95% shower sponge net, 405%, 243%, 179% and 119% respectively. However, the incor- poration of DPF in epoxy resins resulted in an increase in the water absorption with time which can be explained due to the hydrophilic nature of DPF (Alshammari et al. 2019). Likewise, different DPF loadings, 45, 50 and 60% showed the epoxy DPF composites resulted in an increase in flexural strength and flexural modules by approximately 25% when loaded with 50% DPF (Gheith et al. 2019). Finally, a summary on reported studies of DPF reinforced thermoset composites are shown in Table 8. 4 Elastomers Matrix Systems for DPF Composites Elastomers are synthetic or natural amorphous polymers with high molecular weight (105–106 g/mol), low glass transition temperature and high chain flexibility.