In general, polyimides are made by reacting a dianhydride with an aromatic amine

 In general, polyimides are made by reacting a dianhydride with an aromatic amine shower scrunchie. Because of this ring structure, polyimides offer outstanding thermal stability. The demand of polyimides originates from their outstanding thermal properties and thermo-oxidative resistance in combi- nation with excellent mechanical properties puff sleeve bodysuit. Polyimides burn but they have self- extinguishing properties. They have a very low dielectric constant and are resistant to ionising radiation. Among the low-cost thermoset resins, phenolic resin has a thermal 140 S. Awad et al. stability comparable with polyimides. However, phenolic resin is extremely brittle and generally needs blending with other resins like epoxy/polyurethane or rubber for augmenting toughness. Such modifications significantly reduce their thermal stability and they cannot be used for high-temperature structural applications. Poly- imides, due to their high strength and high heat resistance, often replace glass and metals (e.g., steel) in many demanding industrial applications. 

The thermosetting polyimides have aroused tremendous interest as advanced materials in civilian and defence applications (Ratna 2009). Thus, the properties that polyimide resins possess make them suitable as a polymer matrix for developing DPF composites that can be used in structural applications. Amino resins Amino resins are produced by reacting compounds that contain amino group and formaldehyde. Amino resins are used as curing agents for the resins containing carboxyl, hydroxyl and amide groups. The most popular amino resins are urea– formaldehyde (UF) resins and melamine–formaldehyde (MF) resins which are produced by reacting formaldehyde with urea and melamine, respectively (Ibeh 1999). They are considered to supplement and complement phenolic resins. Also, they can replace phenolic resins applications. MF resin shows the best performance in terms of toughness and water absorption. However, the use of MF resin is restricted due to its high cost (Ratna 2009) (Tables 6 and 7). 3.2 Bio-based Thermoset Resins for DPF Composites Bio-based thermoset resins can standout when compared to synthetic thermoset resins by having many advantages, such as low price, universal availability, less hazardous, and is mostly preferred by chemical industries as an alternative to conventional synthetic thermoset resins. There is an extensive demand for bio-based resins in the industries to develop sustainable composites that can perform similarly to synthetic polymers (Tschan et al. 2012; Voirin et al. 2014; Zini and Scandola 2016). This section discusses several types of bio-based thermoset resins, their properties and applications. Bio-based PU resins 

Vegetable oils like castor oil for example can be utilized to produce bio-based ther- moset PU resins puff body rock, which have also been exploited in natural fibre composites shower sponge exfoliating. The castor oil triglyceride is distinguished by the existence of ricinoleic fatty acid that contains double bonds as well as hydroxyl groups on its backbone (Crosky et al. 2013). Castor oil- based polyurethane (COPU) can be formed by reacting hydroxyl groups with isocyanates. The produced COPU matrix resin has a tensile strength of 2.5 MPa, much lower than the tensile strength of synthetic thermoset resins, but has an extremely high elongation to break of 31% (Milanese et al. 2011). PU can also be Polymer Matrix Systems Used for Date Palm Composite Reinforcement 141 shrinkage Mold (%) 4–8 1–2 – – – ) heat 2013l. ta Specific (kJ/kg/°C) 1.20 – 1.50 1.40 1.10 yeskro vity ;C 2016 Thermal conducti (W/m/°C) 0.70 0.23–0.24 0.20 0.25