Curing Of Unsaturated Polyesters Research Articles

Hardening condition of unsaturated polyether from alcoholysis products of secondary polyethylene terephthalate

The technological parameters of the curing of unsaturated polyesters synthesized on the basis of alcoholysis products of secondary polyethylene terephthalate and used in the production of fiberglass pipes have been studied. It is shown that unsaturated polyesters synthesized on the basis of alcoholysis products can completely substitute imported resins of 196 and 196A grades in the production of fi berglass pipes.

Gel time prediction of polyester resin for lamination of polymer composites

Lamination of fibre reinforced plastics (FRP) and catalytic curing of unsaturated polyester (UP) resin were the major focus of this study. The polyester resin was cured at ambient temperature with methyl ethyl ketone peroxide (MEKP) catalyst, cobalt octoate accelerator and phenol inhibitor. This was used to generate model equations that can predict the gel time of polyester resin when curing additives are added. The gelation was obtained by stirring 20 g of catalysed UP resin weighed into a plastic container until the viscosity suddenly increased. Gel times obtained were subjected to regression analysis and analysis of variance (ANOVA) so as to obtain the best predictive model. The ANOVA result showed that the gel time (Ti) in terms of inhibitor concentration, Ti = 2820i – 6 was the best predictive equation of the gel time with a degree of accuracy of 98.89%; where i is the inhibitor concentration. In the model, catalyst and accelerator are at constant concentrations of 1% and 0.5%, respectively. The model was validated by laminating pilot components using hand lay-up technique. Thereafter, a laminating template was developed that would aid in reducing material wastes and lengthy down time during FRP lamination. This will be useful in increasing productivity and profitability in FRP small scale industry.
 
 Bull. Chem. Soc. Ethiop. 2020, 34(1), 163-174.
 DOI: https://dx.doi.org/10.4314/bcse.v34i1.16

Graphite Nanosheet as Low Shrinkage Additive, Curing Accelerator, and Conducting Filler for Unsaturated Polyester Resin

ABSTRACTThe effect of graphite nanosheets on electrical properties, curing behavior, and polymerization shrinkage of unsaturated polyester resin has been investigated. A solution of polystyrene was used as low profile additive to reduce shrinkage. The results showed that graphite nanosheets have been well dispersed/distributed in the unsaturated polyester matrix where they have high aspect ratio and high surface area. Graphite nanosheet exhibited an accelerating effect on the curing of unsaturated polyester and reduced the polymerization shrinkage as low as 3.6%. Despite large reduction of flexural properties by low profile additive, graphite nanosheet considerably increased the flexural strength and modulus of unsaturated polyester/low profile additive by 47 and 103%, respectively. Therefore, graphite nanosheet can be used as a new low profile additive for unsaturated polyester resins where it is also able to improve mechanical properties and curing rate.

Cure modelling of polyester thermosets in a glass mould

The curing of unsaturated polyester was studied experimentally and using a model of the process. The kinetic parameters were calculated from the heat flow–time curves obtained by differential scanning calorimetry (Mettler Toledo DSC 823), operating in a non-isothermal mode. The temperature–time histories were studied in a cylindrical glass mould. A potential use of glass as a mould for polymer curing is found in the production of optical sensors. Here, glass was selected as a mould material because it is UV transparent, chemically inert and easy to clean. The thermal properties of glass moulds coupled with the intrinsic curing kinetics are of a significant interest in such investigations. Taking into account the heat transferred by the convection from the air to the mould surface and the conduction through the mould wall and resin, as well as the kinetics of the heat generated in the cure reaction, a numerical model has been constructed. The contributions to the rise in temperature from the heat conduction and chemical reaction are different in different parts of the composite, which can explain the temperature–time histories. The introduction of a carbonate based filler reduced the amount of heat released in the composite and, as a result, lowered the temperatures through the resin. A good agreement between experimental data and the predicted mathematical model of the curing process in the mould has been observed.

Mathematical Model for Autoclave Curing of Unsaturated Polyester Based Composite Materials

Heat transfer process involved in the autoclave curing of fiber-reinforced thermosetting composites is investigated numerically. A model for the prediction of the temperature and the extent of the reaction across the laminate thickness during curing process in the autoclave of unsaturated polyester based composite has been developed. The governing equation for one dimensional heat transfer, and accounting for the heat generation due to the exothermic cure reaction in the composites had been used. It was found that the temperature at the central of the laminate increases up to the external imposed temperature, because of the thermal conductivity of the resin and fiber. The heat generated by the exothermic reaction of the resin is not adequately removed; the increase in the temperature at the center increases the resins rate reaction, which in turn generates more heat.

Influence of Residual Polyesterification Catalysts on the Curing of Polyesters

Unsaturated polyesters are synthesized by means of polyesterification, often with catalysts like strong acids, metal oxides and metal-organic salts. Most often, the catalysts used cannot be separated from the bulk of the polyester. Also, some organic or inorganic additives – called fillers – which are used with the polyester in order to decrease cost, affect the curing of the polyester. In this work the effect of residual catalyst on the curing of unsaturated polyester is studied. Unsaturated polyesters were prepared using propylene glycol with a 10% molar excess over stoichiometry and a mixture of dicarboxylic acids, namely maleic acid (unsaturated) adipic acid (saturated) and phthalic anhydride (saturated) at a molar ratio 1:2:2. Lead dioxide, p-toluenesulfonic acid and zinc acetate were used as catalysts, at 0.1% w/w. After the polyesterification, the polymers were diluted with styrene at a proportion of 100:30 w/w. The resins were cured by using MEKP (methylethylketone peroxide) as initiator and CoNp (cobalt naphthenate) as accelerator. Catalysts affect the final color of the polyester. The kinetics of curing of the resins was studied by DSC analysis based on the exothermic peak due to the double bonds breaking to give crosslinked macromolecules. The heat released ΔH is decreased by the presence of catalyst, while activation energy, the frequency factor and the order of reaction are increased.

Curing of Unsaturated Polyester: Network Formation

Unsaturated polyester resins in styrene as comonomer solvent gels to a thermoset stageby network formation due to free radicals produced by the redox reaction between cobalt octoate (promoter) and methyl ethyl ketone peroxide (MEKP) as initiator. Gel times can be reduced or enhanced by the use of N,N-Dimethyl aniline (DMA) or pyridine respectively. The technique of hand lay-up for producing glass reinforced fiber (GRF) is described.

Radical‐initiated curing of unsaturated polyesters with styrene. role of polymer‐bound versus free tertiary amine accelerators

AbstractPolyester prepolymers, prepared from maleic anhydride and diethylene glycol were cured with styrene using benzoyl peroxide as the catalyst and tertiary amines as accelerators. The effect of the accelerators on curing rates and efficiencies and resin properties was studied when the accelerators were chemically incorporated into the polyester prepolymer versus when the same accelerators were free. The accelerators employed were diethylaniline (1); N,N‐bis‐(2‐hydroxyethyl)aniline (2); N,N‐bis(2‐hydroxyethyl)propylamine (3); N,N‐bis(2‐hydroxyethyl)‐isopropylamine (4); N,N‐bis(2‐hydroxyethyl)butylamine (5); and dimethylaniline. The efficiency of the free accelerators decreased in the order dimethylaniline > 1 > 2 > 4 > 3 > 5. Each of the accelerators, 2–5, were significantly more efficient when incorporated into the polymer chain than when they were used free according to measured curing times, pot life, and gel times. Furthermore, the initiation energies for polymer‐bound accelerators 3, 4, and 5 are significantly lower than those obtained when these same accelerators are added free. Polymerbound accelerators 2, 3, 4, and 5 gave resins with higher Brinell's hardness, higher tensile strengths, higher softening points, and lower extractable fractions than were obtained for resins prepared with identical amounts of the corresponding free accelerators. Mechanisms to account for these results are suggested.