Effects of the Addition of Amino-Terminated Highly Branched Polyurea on Curing Properties of Phenol-Formaldehyde Resin

In this work, a highly branched polyurea (HBP-NH₂) similar to urea structure was introduced to phenol-formaldehyde (PF) resin to accelerate itscuring speed The results of gel time and bonding strength were combined to obtain a good modified additional stage and amount of HBP-NH₂. The relative molar mass changes of HBP-NH₂-modified PF resin were investigated by gel permeation chromatography (GPC). The effects of HBP-NH₂ on the curing of PF resin were investigated by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The effect of HBP-NH₂ on the structure of PF resin was also investigated by nuclear magnetic resonance carbon spectroscopy (¹³C-NMR). The test results show that the gel time of the modified PF resin was reduced by 32% and 51% at 110 °C and 130 °C, respectively. Meanwhile, the addition of HBP-NH₂ increased the relative molar mass of PF resin. The bonding strength test showed that the bonding strength of modified PF resin increased by 22% after soaking in boiling water (93 °C ± 2) for 3 h. The DSC and DMA analysis indicated that the curing peak temperature decreased from 137 °C to 102 °C, and the curing rate of the modified PF resin was also faster than that of the pure PF resin. The ¹³C-NMR results showed that HBP-NH₂ in the PF resin reacted to produce a co-condensation structure. Finally, the possible reaction mechanism of HBP-NH₂ for the modification of PF resin was given.

Rheological Analysis of the Synthesis of High-Molecular-Weight Epoxy Resins from Modified Soybean Oil and Bisphenol A or BPA-Based Epoxy Resins

The research undertaken in this work is one of the examples of the engineering of modern polymer materials. This manuscript presents studies on the gelation process which might occur during the synthesis of epoxy resin using the modified vegetable oil via the epoxy fusion process conducted in bulk. Based on obtained results we determined rheological parameters related to the properties of reacting mixture during the polyaddition process, especially before and after occurring the phenomenon of gelation (via (1) theoretical determination of the gel point using the degree of conversion of reactants before occurring the gelation process of reacting mixture and (2) experimentally-the dynamic mechanical properties such as storage modulus, G'; loss modulus, G″; and loss tangent, tg δ). Theoretical investigations show that for both systems: epoxidized soybean oil and bisphenol A (ESBO_BPA), as well as the hydroxylated soybean oil and low molecular weight epoxy resin (SMEG_EPR), theoretical values of the degree of conversion at the gel point are characterized by similar values (ESBO_BPA: xgel-theoretical = 0.620, xgel-theoretical = 0.620 and SMEG_EPR: xgel-theoretical = 0.614, xgel-experiment = 0.630, respectively), while the one determined based on the initial assumptions are greater than the above-mentioned (ESBO_BPA: xgel-assumed = 0.696 and SMEG_EPR: xgel-assumed = 0.667). Moreover, experimental studies in the viscoelastic fluid stage showed that the SMEG_EPR system is characterized by lower values of G' and G″, which indicates lower elasticity and lower viscosity than the epoxidized derivative. It was found that alike during the conventional polyaddition reaction, both systems initially are homogeneous liquids of increasing viscosity. Wherein gradual increase in viscosity of the reaction mixture is related to the fusion of oligomer molecules and the formation of higher molecular weight products. In the critical stage of the process, known as the gelation point, the reaction mixture converts into the solid form, containing an insoluble cross-linked polymer.

Effect of pre-curing process on epoxy resin foaming using carbon dioxide as blowing agent

A thermosetting epoxy resin system consisting of diglycidylether of bisphenol A (DGEBA) and m-xylylenediamine (MXDA) was successfully foamed by carbon dioxide (CO2) using two-step batch process. Isothermal curing kinetics of epoxy system was developed to help control the pre-curing degree of resin under different pre-curing conditions. Samples with different pre-curing degrees were prepared and then foamed via temperature-rising foaming process. It was found that the pre-curing degree was a crucial index for the foamability of epoxy resin. The effects of pre-curing conditions on curing reaction as well as further foaming results were investigated, and the results showed that the pre-curing degree from 37.7% to 46.3% was the proper foaming range for the chosen epoxy resin. With increasing pre-curing degrees from 37.7% to 51.6%, viscosity and elasticity of pre-cured resins increased, and correspondingly, average cell size of epoxy foams decreased from 329.8 µm to 60.8 µm while cell density increased from 1.4 × 105 cells/cm3 to 8.6 × 105 cells/cm3. Furthermore, the foamed samples with the same pre-curing degree had similar cell morphology regardless of pre-curing conditions.

Separator Membrane from Crosslinked Poly(Vinyl Alcohol) and Poly(Methyl Vinyl Ether-alt-Maleic Anhydride)

In this work, we report separator membranes from crosslinking of two polymers, such as poly vinyl alcohol (PVA) with an ionic polymer poly(methyl vinyl ether-alt-maleic anhydride) (PMVE-MA). Such interpolymer-networked systems were extensively used for biomedical and desalination applications but they were not examined for their potential use as membranes or separators for batteries. Therefore, the chemical interactions between these two polymers and the influence of such crosslinking on physicochemical properties of the membrane are systematically investigated through rheology and by critical gel point study. The hydrogen bonding and the chemical interaction between PMVE-MA and PVA resulted in highly cross-linked membranes. Effect of the molecular weight of PVA on the membrane properties was also examined. The developed membranes were extensively characterized by studying their physicochemical properties (water uptake, swelling ratio, and conductivity), thermal and electrochemical properties using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermo-gravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). The DSC study shows the presence of a single T_g in the membranes indicating compatibility of the two polymers in flexible and transparent films. The membranes show good stability and ion conductivity suitable for separator applications.