Polyurethane elastomers (PUR) based on polypropylene glycol and 4,4 0-diphenylmethane diisocyanate were prepared with various monoethylene glycol (mEG) contents. The aim of this study is to find a reliable polymer matrix for composites of improved thermal conductivity and testing fully in order to collect knowledge about its structure. Thermal conductivity was improved from 0.255 to 0.329 W m-1 K-1 when increasing chain extender content. This attributed to a high appearance crystalline ordering level when adding high mEG content. Differential scanning calorimetry revealed a low transition temperature of soft segment at the same temperature around-64°C, due to constant polyol content. The enthalpy of melting increases with increasing mEG content. This is due to the increasing crystalline phase and hard segment phase separation within the PUR structure. Dynamic mechanical analysis results show the glass transition temperature of soft segment in the same temperature range between-57 and-52°C and intensity peak of tand tends to decrease when mEG content was increased. On the other hand, the glass transition temperature of hard segment tends to increase from 10 to 93°C and has high intensity peak of tand with increasing mEG content. Increasing the chain extender content can be enhancing the hard segment length in PUR structure and affecting both soft segment motion and hard segment motion. Increasing hard segment length might be obstructing soft segment motion and influence hard segment motion which is hard to move at low temperatures. Phase separation of soft and hard segment clearly observed using the DMA technique.
In this work, we used the design strategy “doped nonpolar polymers” and synthesized the polyurethane elastomers (PUEs) by doping with highly polar aromatic molecules such as benzoic acid (BA), 4(para)-nitro-benzoic acid (PNBA), and 3, 5-di-nitro-benzoic acid (3, 5-DNBA) by using the solution casting method. The effect of each molecule in three different weight percentages 2%, 4%, and 6% on electrical and thermo-mechanical properties of the material has studied. Experiments were carried out to determine electrical properties such as DC volume resistivity, dielectric constant, and loss factor. DMA and DSC measurements were done to assess thermo-mechanical properties. Also, thermal conductivity measurement was carried out and a strong nitro group and doping percentage dependent results have been observed. A comparative analysis of the effect on the said properties was done among the doped and undoped PUEs.
In this article, flexible and rigid polyurethane (PU)/copper (Cu) composites are prepared via a simple and cost-effective solution casting process. The filler dispersion and chemical bonding of composites are investigated by SEM and FTIR techniques. The results showed the homogeneous dispersion of Cu microparticles. Furthermore, thermal properties are investigated using DMA, DSC, and thermal conductivity measurements. The maximum improvement in thermal conductivity for flexible and rigid PU composites is 24%, and 48%, respectively, as compared to their pure counterparts. The obtained thermal conductivity values are also compared and analyzed with the mechanical property model (Corans and Patel model) and found in good agreement with the output of the model. DMA results showed enhancement in the storage modulus with filler loading while the DSC results revealed the endothermic temperature did not significantly change with adding Cu filler in both flexible and rigid PU matrices. The mechanical properties of composites were studied using tensile and hardness (Shore A and Shore D) test. For flexible PU composites an improvement in tensile strength (43%), Young's modulus (111%), Shore A hardness (6%), Shore D hardness (27%) as compared to pure flexible PU. For rigid PU composites a reduction in tensile strength (23%), Young's modulus (32%), and an increase in Shore A hardness (3%), Shore D hardness (5%) as compared to pure rigid PU. As a result of the current study, TC of rigid PU is found doubly enhanced compared to flexible PU at the same filler concentration. Copper microparticles can act as active filler in both flexible and rigid PU matrices.
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