Cure kinetics and rheology characterization of soy-based epoxy resin system

Effects of the Temperature-Time Regime of Curing of Composite Patch on Repair Process Efficiency

Repair procedures with the use of composite patches are considered to be the most effective among the current technologies of repair of the structures of various applications. In the process of moulding-on of a patch made of polymeric composite material by means of curing, technological stresses arise in the patch. Determination of residual technological stresses is a priority task for the modelling of the repair process. Reduction of residual stresses can be achieved by optimization of the mode of repair patch curing. For meeting this objective, the method for determination of technological stresses, which arise in the structure under repair in the process of curing of a composite patch, has been developed. The method takes into account the shrinkage, change in physico-mechanical characteristics, rheological processes occurring in the binder during moulding process, and determination of stresses in the structure under repair at any time. Therefore, premature failure of the repair joint at the stage of repair can be avoided. It is shown that the method adequately describes the level of deformations and stresses in the structure being repaired at the stage of heating and holding of the composite patch. Increase in the moulding temperature leads to a reduction in residual stresses in the structure under repair. However, current stresses at the stages of heating and temperature holding are increased significantly. Reliability of assumptions and developed method is confirmed by the comparison with the experimental data. The obtained experimental graph of total deformation of the composite patch allowed us to clearly determine the moment of residual stress occurrence in the structure under repair. This moment matches quite exactly (with the discrepancy not exceeding 5 min) the gel point determined analytically based on dependence of the degree of curing on the moulding mode. Consequently, the research together with the results previously obtained allows making an integrated choice of geometric parameters of the repair composite patch and temperature-time regime of its curing in order to ensure the specified level of strength and stiffness of the structure under repair.

Plant oil-based polymers

Polymer materials derived from natural resources have gained increasing attention in recent years because of the uncertainties concerning petroleum supply and prices in the future as well as their environmental pollution problems. As one of the most abundant renewable resources, plant oils are suitable starting materials for polymers because of their low cost, the rich chemistry that their triglyceride structure provides, and their potential biodegradability. This chapter covers the structure, modification of triglycerides and their derivatives as well as synthesis of polymers therefrom. The remarkable advances during the last two decades in organic synthesis using plant oils and the basic oleochemicals derived from them are selectively reported and updated. Various methods, such as condensation, radical/cationic polymerization, metathesis procedure, and living polymerization, have also been applied in constructing oil-based polymers. Based on the advance of these changes, traditional polymers such as polyamides, polyesters, and epoxy resins have been renewed. Partial oil-based polymers have already been applied in some industrial areas and recent developments in this field offer promising new opportunities.

Dual-band in situ molecular spectroscopy using single-sized Al-disk perfect absorbers

We propose antenna-enhanced infrared vibrational spectroscopy by adopting single-sized Al disks on Al2O3-Al films fabricated by colloidal-mask lithography. The precisely designed plasmonic resonator with dual-band perfect absorption (DPA) shows strongly-enhanced nearfield intensity and polarization independence, at both resonances, providing a powerful antenna platform for the multi-band vibrational sensing. As a proof of concept, we experimentally apply the plasmonic DPAs in bond-selective dual-band infrared sensing of an ultrathin polydimethylsiloxane (PDMS) film, simultaneously amplifying two representative vibrational bands (asymmetric C-H stretching of CH3 at 2962 cm-1 and CH3 deformation of Si-CH3 at 1263 cm-1) by surface-enhanced infrared absorption spectroscopy (SEIRA). The plasmonic DPA was successfully adopted for the in situ monitoring of reaction kinetics, by recording the spectral changes in C-H stretching and Si-CH3 deformation modes of a 10 nm PDMS elastomer, which are selectively enhanced by the two antenna resonances, during its gelation process. Our systematic study of the SEIRA spectra has demonstrated mode splitting and a clear avoided-crossing in the dispersion curve as a function of resonance frequency of DPA, manifesting itself as a promising basis for future polaritonic devices utilizing the hybridization between the molecular vibrational states and the enhanced light field.

Cure Cycle Optimization of Rapidly Cured Out-Of-Autoclave Composites

Out-of-autoclave prepreg typically needs a long cure cycle to guarantee good properties as the result of low processing pressure applied. It is essential to reduce the manufacturing time, achieve real cost reduction, and take full advantage of out-of-autoclave process. The focus of this paper is to reduce the cure cycle time and production cost while maintaining high laminate quality. A rapidly cured out-of-autoclave resin and relative prepreg were independently developed. To determine a suitable rapid cure procedure for the developed prepreg, the effect of heating rate, initial cure temperature, dwelling time, and post-cure time on the final laminate quality were evaluated and the factors were then optimized. As a result, a rapid cure procedure was determined. The results showed that the resin infiltration could be completed at the end of the initial cure stage and no obvious void could be seen in the laminate at this time. The laminate could achieve good internal quality using the optimized cure procedure. The mechanical test results showed that the laminates had a fiber volume fraction of 59-60% with a final glass transition temperature of 205 °C and excellent mechanical strength especially the flexural properties.

Effect of the particle diameter of the chemical foaming agent on the foaming process and the cellular structure of one-shot compression molded polyethylene foams

We investigated the effect of varying the particle diameter and the particle content of a chemical foaming agent on the foaming process and the cellular structure of one-shot compression molded polyethylene foams. We foamed metallocene linear low-density polyethylene (LLDPE) crosslinked by dicumyl peroxide using azodicarbonamide (ADCA) as the foaming agent. We used a purpose-built metal mold equipped with a built-in pressure sensor to monitor the time evolution of the cavity pressure. The time dependence of the cavity pressure, which is indicative of the thermal decomposition of the ADCA, was s-shaped. The s-shaped time dependence of the cavity pressure indicates that, after an initial induction phase during which there is no thermal decomposition of the ADCA, the ADCA rapidly decomposes until the reaction is essentially complete. The cavity pressure at saturation, which corresponds to the mass of the generated gas, was linearly proportional to the ADCA content but only weakly dependent on the particle diameter of the ADCA. Upon decreasing the particle diameter of ADCA, rise in the cavity pressure at intermediate times, which indicates the thermal decomposition of the ADCA, began earlier and was faster. The cell size in the final foam decreased with a decrease in the particle diameter of the ADCA. The cell number density in the unfoamed samples (NF ) was proportional to the ADCA particle number density in the unfoamed samples (NC ), with a proportionality constant less than 1. A model for the foaming process where the ADCA particles nucleate cells and the nucleated cells then coalesce, thereby reducing the number of remaining cells, can offer an explanation for the observed proportionality between NF and NC and the proportionality constant being less than 1. Furthermore, it is proposed that cell coalescence occurs if the increase in the moduli of the LLDPE due to crosslinking is not sufficient to prevent the coalescence of the cells triggered by the rapid increase in the cavity pressure due to the rapid decomposition of ADCA.