Liquid epoxy resins have received much attention from both academia and the chemical industry as eco-friendly volatile organic compound (VOC)-free alternatives for applications in coatings and adhesives, especially in those used in households. Epoxy resins show high chemical resistance and high creep resistance. However, due to their brittleness and lack of thermal stability, additional fillers are needed for improving the mechanical and thermal properties. Halloysite nanotubes (HNTs) are naturally abundant, inexpensive, and eco-friendly clay minerals that are known to improve the mechanical and thermal properties of epoxy composites after suitable surface modification. Zirconium is well known for its high resistance to heat and wear. In this work, zirconium oxide-impregnated HNTs (Zr/HNTs) were added to epoxy resins to obtain epoxy composites with improved mechanical and thermal properties. Zr/HNTs were characterized by field-emission transmission electron microscopy, transmission electron microscopy with energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Changes in the thermal properties of the epoxy composites were characterized by thermo mechanical analysis and differential scanning calorimetry. Furthermore, flexural properties of the composites were analyzed using a universal testing machine.

Epoxy resins are commonly used to manufacture the molding compounds, reinforced plastics, coatings, or adhesives required in various industries. However, the demand for new epoxy resins has increased to satisfy diverse industrial requirements such as enhanced mechanical properties, thermal stability, or electrical properties. Therefore, in this study, we synthesized new epoxy resin (PPME) by modifying phosphorous-containing polyol. The prepared resin was analyzed and added to epoxy compositions in various quantities. The compositions were cured at high temperatures to obtain plastics to further test the mechanical and thermal properties of the epoxy resin. The measured tensile and flexural strength of epoxy compositions were similar to the composition without synthesized epoxy resin. However, the heat release rates of the compositions exhibited tendencies of a decrease proportional to the amount of PPME.

In this study, a phosphorous-containing polyol (P-polyol) was synthesized and reacted with isophorone diisocyanate (IPDI) to produce water-dispersed polyurethane. To synthesize waterborne polyurethanes (WPUs), mixtures of P-polyol and polycarbonate diol (PCD) were reacted with IPDI, followed by the addition of dimethylol propionic acid, to confer hydrophilicity to the produced polyurethane. An excess amount of water was used to disperse polyurethane in water, and the terminal isocyanate groups of the resulting WPUs were capped with ethylene diamine. P-polyol:PCD molar ratios of 0.1:0.9, 0.2:0.8, and 0.3:0.7 were used to synthesize WPUs. The films prepared by casting and drying the synthesized WPUs in plastic Petri dishes were used to test the changes in physical properties induced by changing the P-polyol:PCD molar ratio. The experimental results revealed that the tensile strength of PU-10, the WPU with a P-polyol:PCD molar ratio of 0.1:0.9, was 16% higher than that of the reference P-polyol–free WPU sample. Moreover, the thermal decomposition temperature of PU-10 was 27 °C higher than that of the reference sample.

A flame retardant polyol (EP-DOPO) with epoxy functional groups was synthesized by reacting a 1,6-hexanediol glycidyl ether with a flame retardant 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO). The polyurethane (EPPU) with enhanced heat resistance was prepared by the reaction of a polyol blend of EP-DOPO and polytetrahydrofuran (PolyTHF) at a ratio of 1:1 with isophorone diisocyanate. EPPU useful for the preparation of cables or coatings showed higher thermal decomposition temperature rather than that of reference polyurethane synthesized by the reaction between pure PolyTHF and isophorone diisocyanate by thermogravimetric analysis. Further study of the polyurethane as a toughening agent for epoxy polymers was carried out. Epoxy compositions consisting of bisphenol A epoxy resin and dicyandiamide as a hardener have a brittle property allowing crack propagation after cure. Polyurethane plays an important role as an impact modifier to prevent from cracks of epoxy polymers. Various contents of EPPU were added into epoxy compositions to measure the physical property changes of epoxy polymers. The tensile and flexural strengths of the cured specimen were compared with those of epoxy compositions including reference polyurethane. Furthermore, the crosslink density of the cured epoxy compositions was compared.