Academic literature on the topic 'Thermoset resin'

Cure time is often the bottleneck of composite manufacturing processes, therefore it is important to understand the cure of todayâ s thermosetting adhesives. This research attempts to characterize the cure rate of two commercial phenol-formaldehyde adhesives. Two methods are used, parallel-plate rheometry and dielectric spectroscopy. Viscosity data from a parallel-plate rheometer may be used to track the advance of polymerization as a function of temperature. This data can then be used to optimize press conditions and reduce production times and costs. <p> The research will further examine resin cure through dielectric analysis; such a technique could monitor resin cure directly and in real-time press situations. Hot-pressing processes could conceivably no longer require a set press schedule; instead they would be individually set based on dielectric data for every press batch. Such a system may lead to a more efficient and uniform product because press times could be based on individual press cycles instead of entire product lines. A more likely scenario, however, is the use of in situ adhesive cure monitoring for troubleshooting or press schedule development.</p><p> This research characterized the cure of two phenol-formaldehyde resins using parallel-plate rheometry, fringe-field dielectric analysis, and parallel-plate dielectric analysis. The general shape of the storage modulus vs. time curve and the gel and vitrification points in a temperature ramp were found.</p><p> Both dielectric analysis techniques were able to characterize trends in the resin cure and detect points such as vitrification. The two techniques were also found to be comparable when the cure profiles of similar conditions were examined.</p><br>Master of Science

The usual approach to the process modeling of thermoset matrix composites is to divide the analysis into two distinct and sequential steps, first of flow-deformation behaviour and then of stress-deformation. In the current processing models, each of these two aspects is dealt with in a separate sub-model, typically called the flow module and stress module respectively. The flow module is relevant to the pre-gelation behaviour of resin, while the stress module is valid for the post-gelation composite material. In this thesis, the framework to integrate the flow and the stress modules into a unified module in finite element processing models is presented. The work is based on a two-phase model for analysis of resin flow and its resulting deformations in the composite material. Special measures are introduced to provide for additional capability of this model to account for the development of stresses in the curing composite material. These modifications are needed to ensure the accuracy of the model in both of resin flow and stress development regimes, and include the introduction of consistent compressibility in the mass conservation equation of the two-phase system, and a special decomposition of stresses of the system. The formulation is implemented for a pseudo-viscoelastic stress model in a 2D plane strain FE code in MATLAB. The approach may readily be extended to fully viscoelastic models. Various examples from single-element problems dealing with the development of residual stresses throughout a single-hold cure cycle to more geometrically complex composite laminates undergoing standard cure cycles are modeled by the integrated model and comparisons are made in one extreme to the flow-compaction behaviour by the standard flow models, and in the other extreme to the results obtained by the pseudo-viscoelastic approach. The model developed here is a promising tool for simulating processing of large-scale composite structures continuously from the very early stages of the process when the resin behaves in a fluid-like manner all the way to the final stage when it behaves as a 3D solid.

Lactic acid based thermoset were synthesised by reacting lactic acid with glycerol andfunctionalizing lactic acid branches by methacrylic anhydride. Resins with different chainlength were prepared and their thermo mechanical properties were examined through DMAanalysis and their molecular structures were analyzed by NMR method and their viscositywere investigated through rheometry analysis and three monomers were selected as the bestchain length. Degree of reaction in different reaction times was evaluated by a modifiedtitration method and bulk preparation of resin was performed by optimal process condition.DSC analysis was conducted in order to evaluate curing behaviour of resin with benzoylperoxide as cross-linking initiator. TGA analysis was performed to check thermo stability ofthe resin. Bio composites by viscose unidirectional and bidirectional knitted fabrics and alsonon woven viscose fiber with different fiber loads were prepared by ordinary hand layupimpregnation followed by compress moulding and their mechanical and thermo mechanicalproperties were characterized by tensile, flexural, charpy and DMA analysis and optimumfiber loads were identified for each fiber type. Ageing properties of prepared composites wereexamined by placing samples in climate chamber to simulate long time ageing and ageingexperiment was followed by tensile and flexural test to evaluate mechanical properties afterageing simulation. Composite`s swelling properties for water and some other solvents wereinvestigated and also their chemical resistance were evaluated by immersing them in 1M HCland KOH. The resin was also compared with a commercial oil based thermoset by preparingglass fiber reinforced composites and also effect of adding styrene to the resin were evaluated.Results of this work demonstrated that the novel synthesised have very high mechanical andthermo mechanical properties surpassing commercial oil based poly esters but ageingbehaviour is not very good however adding styrene can improve ageing properties. Also theresin is compatible with cellulosic natural fibers and forms strong composites.<br>Program: Masterutbildning i energi- och material

RESUM Les reïnes epoxi constitueixen un dels polímers més emprats en el món de la industria, si bé presenten una sèrie d’inconvenients, els més importants dels quals són: la seva inherent fragilitat, la seva excessiva resistència tèrmica que en dificulta l’eliminació d’un substrat un cop finalitzada la seva vida útil i l’encongiment que experimenten durant el procés de curat. Per tal de reduir o eliminar aquests problemes aquesta tesi proposa l’ús de polímers hiperramificats així com polímers estrella i copolímers lineal-hiperramificat de bloc com a modificants químics de reïnes comercials. Amb aquesta estratègia s’han aconseguit millorar la tenacitat degut a efectes flexibilitzants o a separacions de fase del modificant en la matriu epoxídica, així com reduir l’encongiment en el curat o la degradabilitat de les reïnes, sense afectar altres propietats de la reïna com la seva Tg o la seva duresa.<br>ABSTRACT Epoxy resins are one of the most used polymers in the field of technological applications. However, they present some drawbacks being the most important the following: they are inherently brittle materials; they present excessive thermal resistance that limits their reworkability; and the shrinkage they experiment during curing. To overcome these problems this thesis proposes the use of hyperbranched polymers, as well as star polymers and lineal-hyperbranched block copolymers as chemical modifiers of commercially available epoxy resins. With this strategy tougher materials have been obtained due to either a flexibilizing effect or a phase separation of the modifier within the epoxy matrix. Moreover, the shrinkage on curing and the degradability of the thermosets have been improved without compromising other properties of the resin such as its Tg or its hardness.

The interpretation and modelling of the dielectric response of thermosetting materials during cure was the main focus of this study. The equivalence of complex permittivity and complex impedance in terms of information content was outlined in a series of case studies covering the separate effects of dipolar movements and charge migration as well as the combined effect of the two polarisation mechanisms. Equivalent electrical circuits were used in order to model the evolution of the complex impedance during cure. A numerical method that can model consecutive spectra throughout the cure was developed. The method is based on Genetic Algorithms and requires only input from the modelling of the initial spectra. Complex impedance spectra were collected during the cure of a commercial epoxy resin formulation under isothermal and dynamic heating conditions. The spectra were analysed and modelled. The modelling was successful over the whole frequency range of the measurements (1 Hz – 1 MHz). The analysis of the estimated model parameters showed that charge migration dominates the dielectric response in a wide frequency range. In addition, the modelling algorithm also distinguished between the effects of electrode polarisation and dipolar movements in the signal. A new equivalent circuit was used in order to map the frequency regions where the each one of the three phenomena that together comprise the dielectric signal can be monitored most effectively. A chemical cure kinetics model was developed for the studied system. A correlation between the maximum point of the imaginary impedance spectrum and the reaction conversion was established. A mathematical model, based on a simple linear dependence of the dielectric signal on conversion and temperature, was built. The model predictions agreed well with the experimental data. The aim of simplifying the interpretation of the dielectric signals led to the development of a new experimental technique. Temperature Modulated Dielectric Analysis employs temperature modulations superimposed on an underlying thermal profile in order to separate the influence on the signal of the temperature alone from that of the cure reaction. The early study carried out here shows that such measurements are feasible and reveals important issues for its further development.

Vinylesters are termosets resins that have reactive double bond at the chain ends. They are produced by the reaction of various epoxies and acrylic acids by step growth polymerization. Vinylester chains are oligomers with molecular weight from 600 to 1200 g/mol. The resin viscosity is very high<br>therefore, diluent is used for easy application. The generally used diluent is styrene with, reactive double bonds to form a crosslink between the chains. The diluted resin viscosities are between 200 &amp<br>#8211<br>2000 cps. Peroxide initiators are used for network formation. The mechanical properties of vinylester resin are enhanced with reinforcements such as glass fiber, carbon fiber, Kevlar or nanoparticules to make composites. Various molecular weights of vinylester resins were synthesized and the samples were prepared with different styrene contents. The effects of the styrene content, temperature and molecular weight on the viscosity were measured and examined. The main effects were determined as styrene content and temperature, while the effect of molecular weight is negligible. The resins were characterized with IR and NMR spectroscopy. The molecular weights were determined by theoretical calculations, titration and H-NMR spectroscopy. Peroxide initiators were used to cure the resins with the cobalt complex accelerator. The resins were post-cured at different temperatures. The completion of the curing was monitored by the disappearance of the carbon-carbon double bonds of methacrylate (943 cm-1) and styrene (910 cm-1), by FT-IR spectrum. The effects of styrene content, post-cure conditions, and molecular weight on the mechanical properties were discussed. The glass transition temperatures were determined by DSC and DMA. The crosslink densities and rheological properties were determined by creep test. The important properties of vinylester resins, which are modulus, tensile and flexural strength, shrinkage, water absorption, glass transition temperature, HDT values and impact strength were investigated.