most of thermoplastic polymers which allows them to have a better distribution and contact with natural fibres and they are 100% biodegradable

 most of thermoplastic polymers which allows them to have a better distribution and contact with natural fibres and they are 100% biodegradable. However, tensile strength of PHA copolymers show to be constant upon the loss in molecular weight until below 100 kg/g-mol at which point it decreases dramatically, as the degree of chain entanglement decreases body puff. Also, PHAs havelow thermal stability while melted and while processing some of the PHAs show slow crystallization rate which affects the mechanical properties. Moreover, the utilization of PHA polymer in developing Polymer Matrix Systems Used for Date Palm Composite Reinforcement 135 composites with natural fibre are not yet feasible on a large scale due to the high costs for sterilizing equipment, in combination with a refined carbon source, the productivity limitations for biological processes and the need for an extraction stage, which lead to a high market price of PHA when compared to the costs of conventional polymers such as PVC and PE (Chan et al. 2018). Furthermore, starch is a natural polysaccharide, which is known to be the most abundantly available renewable material worldwide. It can be obtained from a variety of crops, such as maize, potato, corn, pea, cassava and rice. It is 100% biodegradable and edible, which makes it an attractive material for food packaging and biodegrad- able composites development. However, the processing of starch is challenging as it is not a truly thermoplastic, but investigations and studies showed that starch can be altered and by blending with other polymers, by grafting with vinyl monomers or by processing with plasticizers shower puff sponge. It can perform thermoplastic properties in the presence of plasticizers, such as glycerol and water at elevated temperatures (90–180 °C) and under shear. Thus, TPS is a potential candidate to replace synthetic PBP. However, its low mechanical stability and sensitivity to water are considered as the main disad- vantages of TPS when compared to other bio-based polymers. 

The tensile modulus and strength of TPS is in the range of 0.01–1 GPa and 0.20–22.0 MPa respectively, which are much lower than those of PLA and PHA polymers. Upon storage, the stiffness and mechanical characteristics of TPS are weakened due to an aging effect occurred through hydrolysis, known as retrogradation due the diffusion of water into the polymer matrix, and to the recrystallization of amylopectin(Nafchi et al. 2013; Zhang et al. 2014; Chan et al. 2018). Moreover, PCL is a semi-crystalline linear polyester prepared through the ring- opening polymerization of E-caprolactone that is completely biodegradable in compost environments and aerobic soils (Goldberg 1995). PCL is a semi-rigid and tough polymer that has a Tg of 65–60 °C and a low Tm of 58–65 °C. At room temperature, PCL has a modulus of that between LDPE and HDPE shower sponge crossword. Also, PCL is compatible with many polymers and organic materials, thus it is used in many polymer formulations as compatibilizers (Sreekumar and Thomas 2008). 2.3 Thermoplastic Matrix Systems in Date Palm Fibre Composites Research on DPF reinforced thermoplastic composite was initially reported by Abu- Sharkh and Hamid (2004), who investigated the degradation and stabilization of PP/DPF composite under artificial and natural weathering conditions. Results showed that PP/DPF reinforced composite possessed higher stability than PP itself under both accelerated and weathering exposures, and the compatibilized PP/DPF reinforced composite showed substantial degradation compared to uncompatibilized PP/DPF reinforced composites (Abu-Sharkh and Hamid 2004). The effect of DPF rachis, trunk and petiole, at different loading concentrations, 20%, 30% and 40%, on the 136 S. Awad et al. 

mechanical properties of HDPE reinforced composites was also investigated, and the results showed that the addition of more than 20 wt% of DPF from the different parts of DPF produced better mechanical properties than pure HDPE. The optimal fibre content that attained the highest strengths was 40 wt% for the trunk DPF, increasing both the tensile and flexural strength by 17% and 37% respectively. On the other hand, 30 wt% was the optimal fibre loading for both rachis and petiole DPFs, increasing the tensile strength by 15.5% and 6%, and the flexural strength by 8.5% and 60% respectively (Mahdavi et al. 2010). Additionally, AlMaadeed and her colleagues investigated the mechanical and thermal properties of recycled PP (RPP) based hybrid composites of date palm wood flour (DPWF)/glass fibre although only one composite was made from RPP reinforced with 30% DPWF, and found that RPP reinforced DPWF composite has 10% higher tensile strength than pure RPP, where the tensile strength increased from 14.8 to 16.5 MPa. However, the melt flow index (MFI) decreased by 45% reusable shower sponge, from 1.78 to 1.23 g/10 min (AlMaadeed et al. 2012). The addition of the treated DPF with 5% NaOH aqueous solution to reinforce recycled PET matrix was reported to increase both the tensile and flexural strength with the increase of the concentration of DPF, 5, 10 and 15% in the composite.