Study of Effect of NCO/OH Molar Ratio and Molecular Weight of Polyol on the Physico-Mechanical Properties of Polyurethane Plaster Cast
2 Abstract: Polyurethane plaster cast was an open weave fabric bandage, prepared by coating polyurethane prepolymer on raschel knitted fiberglass and polyester fabric. Curing takes place by coming in contact with water to form hard rigid cast. Polyurethane prepolymers were synthesized by reacting molar excess of diphenyl methane diisocyanate (MDI) with polypropylene glycol (PPG) at 60°C for 2 hours. This effect of different NCO/OH molar ratio and molecular weight of polyol on the tack free time, setting time, diametral compression strength, percent elongation and tensile strength of polyurethane plaster cast were investigated.. It was observed that with increase in NCO/OH molar ratio, tack free time and setting time of the cast decreases, whereas diametral compression strength increases. Tensile strength was determined in universal testing machine and was found to increase with increasing NCO/OH ratio while opposite trend was observed in case of percent elongation. With increase in polyol molecular weight, tack free time and setting time of the cast increases, whereas diametral compression strength decreases. Blended polyols i.e. PPG 1000 with PPG 400 in 50/50 ratio gives tensile strength and diametral compression strength in between their unblended counterparts. In comparison to fiberglass cast, polyester cast has higher percent elongation and diametral compression strength.
Effect of NCO/OH ratio on physical and mechanical properties of castor-based polyurethane grouting materials
This research focused on fabrication of castor-based PU grout (CPUG) using castor oil with OH value of 161 mg/KOH/g and MDI with NCO content of 31%. The effect of different NCO/OH ratio on the foam reaction time, density, rheology, morphological and mechanical properties were investigated. The result shows that the rise time of CPUG decreased while tack free time increased with the increased of NCO/OH ratio. Morphological properties shows that CPUG consist of closed cell of foams and the diameter of a single cell foam decreased with the increased of NCO/OH ratio. The apparent density, rheology index, flexural strength, flexural modulus and compression strength of CPUG increased with the increasing NCO/OH ratio. CPUG’s apparent density was in the range of 230.23 kg/m3 while rheology index of CPUG was between 1.74 to 2.43 cm/g. Both values obtained were in the range of industrial PU grout’s density and rheology index (214 kg/m3 & 1.48 cm/g). CPUG4 give the best flexural and compression strength with a value of 11.01Mpa and 2Mpa respectively. Flexural and compression strength of CPUG were tantamount to the industrial PU grout’s properties which the average of flexural strength and compression strength were about 7.4MPa and 2MPa respectively.
Development of polyurethane engineering thermoplastics. II. Structure and properties
Rigid, tough thermoplastic polyurethanes were synthesized by a two–step technique. These materials presented a complex structure consisting of a continuous, rigid, amorphous, or semicrystalline matrix with a dispersed soft phase. The influence of soft–segment content upon rigidity modulus, heat–distortion temperature, and fracture behavior has been deter-mined on model amorphous polyurethanes. The influence of crystallinity upon final prop-erties has been studied on two materials: a preparation of ours and a commercial product. Various degrees of crystallinity have been induced in the samples by annealing. Phase structure was characterized by differential scanning calorimetry and wide–angle X–ray scat-tering. Some of the polyurethane samples assayed in this paper exhibited similar properties to those reported in respect of more conventional engineering thermoplastics, such as ABS or nylon. © 1993 John Wiley & Sons, Inc.