Thermoset Polymer Matrix Research Articles

Applying Computational Analysis in Studies of Resin Transfer Moulding

Resin Transfer Moulding (RTM) as it is most known process in the Resin Injections family, is an extensively studied and used processing method. This process is used to manufacture advanced composite materials made of fibres embedded in a thermoset polymer matrix. Fibre reinforcement in RTM processing of polymer composites is considered as a fibrous porous medium regarding its infiltration by the polymer resin. In this sense, the present work aims the computational analysis of a fluid in a porous media for a RTM composite moulding by using the ANSYS CFX® commercial software. In order to validate the numerical study of the fluid flow in a known RTM system, experiments was carried out in laboratory to characterize the fluid (vegetal oil) flowing into the porous media (0/90 glass fibre woven), were pressure and fibre volume fraction have been fixed. The numerical simulation provides information about volume fraction, pressure and velocity distribution of the phases (resin and air) inside the porous media. The predicted results were compared with the experimental data and its has shown a solid relationship between them.

Influence of preforming on the quality of curved composite parts manufactured by flexible injection

Flexible Injection is a new processing technique for the manufacture of advanced composites made of continuous reinforcing fibers and thermosetting polymer matrix. The primary objective of this new process is to provide faster and less expensive manufacturing than traditional methods like autoclave processing or Resin Transfer Molding. The present paper investigates the effectiveness of the proposed method to produce composite structures possessing sharp corners. A specially devised setup is used to manufacture out of glass fibers and vinyl ester resin a series of Z-shaped parts with small radii. The quality of the fabricated parts is assessed to detect possible defects induced by the manufacturing process. Each stage of the production cycle is analyzed thoroughly to develop a simplified finite element model reproducing the fiber bed behavior during processing. Parametric studies are conducted to evaluate the impact of processing conditions on the quality of final products. The combination of numerical simulations and experimental observations demonstrates clearly the importance of the preforming stage. At the same time, it provides useful insights on the physical phenomena occurring during Flexible Injection.

Renewable polyol‐based polycarbamates and polycarbamate–formaldehyde thermosetting resins

AbstractSeveral polycarbamates and polycarbamate–formaldehyde (CF) resins were synthesized, and their properties were investigated aiming at developing of useful thermosetting polymer materials from simple polyols including those derived from renewable resources. Polycarbamates synthesized from polyols using two‐step laboratory routes showed good storage stabilities making them suitable as large volume industrial chemicals. Furthermore, syntheses and 13C‐NMR studies of CF resins showed the formation of oligomeric resins having hydroxymethyl and methylene groups with thermosetting curing properties that are similar to those of current urea–formaldehyde (UF) resins. Dynamic mechanical analysis studies showed somewhat slower curing rates for CF resins compared to UF resins. Bonding of particleboard and internal bond and free formaldehyde content measurements indicated high‐bond strength values and very low‐formaldehyde emission potentials for CF resins. The higher functionalities of CF resins appear to be the basis of good performances. Further investigations on scalable synthesis methods for polycarbamates and on the expansion of CF resins' bonding capabilities would need to be investigated in the future. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Zirconium tungstate/cyanate ester nanocomposites with tailored thermal expansivity

The dimensional stability of polymer matrix composites can be enhanced by reducing the mismatch in the coefficient of thermal expansion (CTE) between the high CTE polymer matrix and low CTE fiber reinforcements, which leads to development of residual stresses and matrix microcracking. A potential strategy to diminish these residual stresses involves development of polymer nanocomposites with well dispersed nanoparticles that reduce the extent of mismatch in CTE. In this work, we explore the potential for development of bulk polymer nanocomposites with tailored thermal expansivity through incorporation of zirconium tungstate nanoparticles that are characterized by a negative CTE in a unique low viscosity bisphenol E cyanate ester (BECy) thermosetting polymer matrix. Incorporation of up to 10 vol.% whisker-like nanoparticles, synthesized by a hydrothermal method, results in a 20% reduction in the CTE of the polymer matrix. However, the nanoparticles exert a dramatic catalytic effect on the cure reaction of BECy resin and subsequently decrease the onset temperature of the glass transition for the cured polymer network, at high filler loadings.

Diffusion Crosslinking Kinetics of Thermoset Polymers

The problem of the delayed crosslinking arising due to the diffusion of a crosslinker molecule from a vector particle within a thermoset polymer matrix is discussed. The crosslinker molecules, initially embedded in the vector particles, diffuse from the particle to the polymer matrix and react with the functional groups grafted to polymer chains. The two-step diffusion crosslink kinetics is studied theoretically on the example of polyethylene functionalized with anhydride groups reacting with 1,4-butanediol as a crosslinker molecule. This provides the independent of time limiting distribution functions of the concentration of crosslinks, unreacted and intermediate functional groups, which are shown to be rather sensitive to system parameters as rates of chemical reactions, ratio of diffusion coefficients of matrix to vector particles, stoichiometric composition of the reactive groups, etc. The nonmonotonic distribution of the crosslink concentration around the vector particles at certain range of the parameters is revealed.

On the effect of different polymer matrix and fibre treatment on single fibre pullout test using betelnut fibres

This study is aimed at exploring the possibility of improving the interfacial adhesion strength of betelnut fibres using different chemical treatments namely 4% and 6% of HCl and NaOH respectively. The fibre specimens were partially embedded into different thermosetting polymer matrix (polyester and epoxy) as reinforcement blocks. Single fibre pullout tests were carried out for both the untreated (Ut) and treated betelnut fibres with different resins and tested under dry conditions. Scanning electron microscopy was used to examine the material failure morphology. The studies revealed the differences of interfacial adhesion strengths for the various test specimens of betelnut fibres treated with the polyester and epoxy matrix which followed in the order of: N6 ≫ N4 > H4 > Ut > H6. It was proven that fibres treated with 6% of NaOH exhibits excellent interfacial adhesion properties. The interfacial adhesion shear strength of these fibres using polyester and epoxy has improved by 141% and 115% correspondingly compared to untreated fibre under the same treatment.

プリント配線板を支える高分子材料 プリント配線板の現状と今後の展望

Personal digital assistants (PDA), such as cellular phones, personal computers and car navigation systems, supporting the ubiquitous society, is expected to be the smart phones which have above mentioned all functions and evolve to ultimate wearable PDAs. High density LSI packaging technologies have been realized the superior performance and function of communication electronics products and printed wiring boards have played very important role to meet these requirements. Here, after brief introduction of the history and the categories, the technologies and the recent trend for the printed wiring boards are introduced, especially focusing on the thermosetting polymer materials. As the future prospect, we pay attention to the automotive electronics field, concretely the power device packaging technologies. High heat resistant and low thermal expansion resins such as polyaromatic epoxy resins, benzoxazine resins and cyanate resins for power semiconductor module are developed. Power semiconductor devices are key devices for carbon dioxide reduction technology. As another approach, the effective use of biomass resources as industrial materials plays an important role. Lignin is a plant biomass and is classified as a polyphenol and investigated a suitable alternative to fossil-fuel-derived phenol resins for use in the thermosetting epoxy resins.

Designed-in Molecular Interactions Lead to Superior Thermo-mechanical Properties in Nanocomposites

ABSTRACTThe effect of the nanofiller chemistry on the mechanical behaviour of thermoset polymer matrix nanocomposites is investigated. The interaction between a crosslinked polymer resin and the reinforcing nanofibers driven by their chemistry is revealed by molecular dynamics simulations. Specifically, crosslinked network systems of neat epoxy and epoxy-P(St-co-GMA) are modeled to discuss the effect of various molecular interactions as a function of temperature on a molecular basis. At 433K°, incorporation of single molecule of bonded P(St-co-GMA) and nonbonded P(St-co-GMA) lead to increase in Young’s modulus by 10% and 6%, respectively, compared to neat epoxy system.

Computational Design of Polymer Nanocomposite Coatings: A Multiscale Hierarchical Approach for Barrier Property Prediction

In the development of polymer nanocomposites (PNCs), computational prediction of material properties is of great advantages in achieving rational and cost-effective design. This paper introduces a new multiscale hierarchical approach specifically tailored for PNCs property prediction. Due to its distinct features of generality and comprehensiveness, the introduced methodology outperforms most existing computational methods in this area. By this methodology, a wide range of PNCs containing any-shaped nanoparticles dispersed in a thermoplastic or thermoset polymer matrix can be thoroughly investigated for multiple property prediction. Furthermore, a reliable prediction is promoted by a systematic consideration of the intrinsic multiscale hierarchical structure of PNCs. Most importantly, an effective integration of different methods and theories at individual scales offers unique opportunities for gaining in-depth scientific understandings on the molecular structural origin of macroscopic property enhancement.

Experimental study of tool–part interaction during autoclave processing of thermoset polymer composite structures

Autoclave manufacturing of thermoset polymer matrix composite structures with high dimensional fidelity requires a good understanding of various parameters affecting process-induced warpage and application of this knowledge to minimize the warpage through appropriate process control. One important contributor is the interaction between a composite part and the tool on which the part is laid and cured. This experimental study quantified the tool–part interaction by measuring the static and dynamic frictional coefficients as a function of process time, using a friction test fixture specially designed to simulate the autoclave environment. Temperature ramp rate was varied to understand the effect of autoclave cure cycle on the friction coefficients. Measured friction coefficients were maximum at the start of the cure cycle and varied as a function of degree of cure ( α) and ramp rate owing to change in the tool–part interface, cure shrinkage, resin/composite properties, residual stress, and mode of interface failure.

Mechanics of polymer nanocomposites modified with fulleroid nanofillers

Polymer nacomposites based on thermosetting (epoxy resins) and thermoplastic (PA-12) polymer matrices with fulleroid and carbon modifiers are synthesized through in situ polymerization, and the mechanical properties are investigated. The introduction of fulleroid modifiers has almost no effect on the mechanical properties of thermosetting formulations; however, in the case of thermoplastic formulations, Young’s modulus and tensile strength increase by 30–40% after introduction of 0.02–0.06 wt % fulleroid modifiers.

Preparation and Thermal-Mechanical Characterization of Nanoclay-Unsaturated Polyester Composites

Recently polymer nanocomposites have attracted great interest as much as in industry as in research laboratories, due to they often show remarkable improvement in their mechanical and thermal properties when are compared with the virgin polymers. Among nanocomposites, nanoclay-reinforced polymers have been widely studied, specifically, those formed by a thermosetting polymer matrix, like unsaturated polyester crosslinked resin reinforced with layered silicates, like montmorillonite. In this work we have prepared nanocomposites formed by an isophtalic unsaturated polyester crosslinked resin (UP) reinforced with different contents (2-10 wt%) of organic modified montmorillonite (OMMT). The UP/OMMT nanocomposites have been prepared following different procedures and the structural characterization has been carried out by using X-ray diffraction (XRD). In all the cases an increase of the d-spacing between layers of the OMMT has been detected. The objective of this study is to analyze the thermal and mechanical behaviour of nanocomposites. For all of the reinforced systems, the glass transition temperatures values, Tg, obtained by differential scanning calorimetry (DSC) and dynamic-mechanical thermal analysis, (DMTA) are higher than the corresponding ones to neat UP. On the other hand, the OMMTP mechanical behaviour has been evaluated by DMTA and by tensile tests. Both techniques reveal an increase in Young modulus, however, a decrease of the tensile strength is observed in all the reinforced systems.

Application of Particle Swarm Optimisation to Evaluation of Polymer Cure Kinetics Models

A particle swarm optimisation approach is used to determine the accuracy and experimental relevance of six disparate cure kinetics models. The cure processes of two commercially available thermosetting polymer materials utilised in microelectronics manufacturing applications have been studied using a differential scanning calorimetry system. Numerical models have been fitted to the experimental data using a particle swarm optimisation algorithm which enables the ultimate accuracy of each of the models to be determined. The particle swarm optimisation approach to model fitting proves to be relatively rapid and effective in determining the optimal coefficient set for the cure kinetics models. Results indicate that the singlestep autocatalytic model is able to represent the curing process more accurately than more complex model, with ultimate accuracy likely to be limited by inaccuracies in the processing of the experimental data.

Influence of using nanoobjects as filler on functionality-based energy use of nanocomposites

The goal of our study was to investigate the potential benefits of reinforcing polymer matrices with nanoobjects for structural applications by looking at both the mechanical properties and environmental impacts. For determining the mechanical properties, we applied the material indices defined by Ashby for stiffness and strength. For the calculation of environmental impacts, we applied the life cycle assessment methodology, focusing on non-renewable energy use (NREU). NREU has shown to be a good indicator also for other environmental impacts. We then divided the NREU by the appropriate Ashby index to obtain the ‘functionality-based NREU’. We studied 23 different nanocomposites, based on thermoplastic and thermosetting polymer matrices and organophilic montmorillonite, silica, carbon nanotubes (single-walled and multiwalled) and calcium carbonate as filler. For 17 of these, we saw a decrease of the functionality-based NREU with increasing filler content. We draw the conclusion that the use of nanoobjects as filler can have benefits from both an environmental point of view and with respect to mechanical properties.

Damping, tensile, and impact properties of superelastic shape memory alloy (SMA) fiber-reinforced polymer composites

The potential of superelastic shape memory alloy (SMA) fibers to enhance the damping capacity and toughness of a thermoset polymer matrix was evaluated. A single-fiber winder was designed and built to manufacture a pre-form consisting of 102 μm diameter SMA fibers aligned parallel to each other. This pre-form was loaded to varying amounts of pre-strain and impregnated with vinyl ester to manufacture SMA fiber composites with 20% fiber volume fraction. The composites were tested using a Differential Scanning Calorimeter (DSC) and a Dynamic Mechanical Analysis (DMA), to evaluate the improvement in damping capacity of the polymer matrix due to the SMA fibers. Tensile and instrumented impact testing were carried out to evaluate improvements in mechanical properties and toughness of the composites. Appreciable improvement was observed in damping, tensile, and impact properties of the polymer matrix due to reinforcement with superelastic SMA fibers, highlighting the advantages of their use in polymer composites.

Exposure to nanoscale particles and fibers during machining of hybrid advanced composites containing carbon nanotubes

This study investigated airborne exposures to nanoscale particles and fibers generated during dry and wet abrasive machining of two three-phase advanced composite systems containing carbon nanotubes (CNTs), micron-diameter continuous fibers (carbon or alumina), and thermoset polymer matrices. Exposures were evaluated with a suite of complementary instruments, including real-time particle number concentration and size distribution (0.005–20 μm), electron microscopy, and integrated sampling for fibers and respirable particulate at the source and breathing zone of the operator. Wet cutting, the usual procedure for such composites, did not produce exposures significantly different than background whereas dry cutting, without any emissions controls, provided a worst-case exposure and this article focuses here. Overall particle release levels, peaks in the size distribution of the particles, and surface area of released particles (including size distribution) were not significantly different for composites with and without CNTs. The majority of released particle surface area originated from the respirable (1–10 μm) fraction, whereas the nano fraction contributed ~10% of the surface area. CNTs, either individual or in bundles, were not observed in extensive electron microscopy of collected samples. The mean number concentration of peaks for dry cutting was composite dependent and varied over an order of magnitude with highest values for thicker laminates at the source being >1 × 106 particles cm−3. Concentration of respirable fibers for dry cutting at the source ranged from 2 to 4 fibers cm−3 depending on the composite type. Further investigation is required and underway to determine the effects of various exposure determinants, such as specimen and tool geometry, on particle release and effectiveness of controls.

High Energy Mill Processing of Polymer Based Nanocomposites

Polymer matrix nanocomposites have attracted growing attention due to the potential for significantly improving the properties of the polymer by adding a very small amount of nanoparticles. However, the improvement in properties has been related to the degree of dispersion of the nanoparticles in the polymer matrix and, due to their enormous specific surface area, nanoparticles tend to agglomerate. Thus, processing techniques able to produce complete particle dispersion in polymer matrix are of great interest. The purpose of this work is to present a new processing technique for polymer matrix nanocomposites using a high energy mill as an effective approach to disperse ceramic nanoparticles in a polymer matrix. SiO2/epoxy nanocomposites were processed with various SiO2 contents using the proposed approach. Transmission electron microscopy (TEM) micrographs of the nanocomposites processed indicated good particle dispersion. In addition, agglomerates were not observed on the scanning electron microscopy (SEM) fractographs of the nanocomposites, up to 3wt% SiO2. The processed nanocomposites were also characterized by dynamic mechanical analysis (DMA) to investigate the effect of nanoparticles content on the viscoelastic properties and on the glass transition temperature. In summary, the technique was found promising in achieving good levels of particle dispersion in a thermoset polymer matrix.

Multiphysics simulation of microwave curing in micro‐electronics packaging applications

PurposeThis paper aims to present an open‐ended microwave curing system for microelectronics components and a numerical analysis framework for virtual testing and prototyping of the system, enabling design of physical prototypes to be optimized, expediting the development process.Design/methodology/approachAn open‐ended microwave oven system able to enhance the cure process for thermosetting polymer materials utilised in microelectronics applications is presented. The system is designed to be mounted on a precision placement machine enabling curing of individual components on a circuit board. The design of the system allows the heating pattern and heating rate to be carefully controlled optimising cure rate and cure quality. A multi‐physics analysis approach has been adopted to form a numerical model capable of capturing the complex coupling that exists between physical processes. Electromagnetic analysis has been performed using a Yee finite‐difference time‐domain scheme, while an unstructured finite volume method has been utilized to perform thermophysical analysis. The two solvers are coupled using a sampling‐based cross‐mapping algorithm.FindingsThe numerical results obtained demonstrate that the numerical model is able to obtain solutions for distribution of temperature, rate of cure, degree of cure and thermally induced stresses within an idealised polymer load heated by the proposed microwave system.Research limitations/implicationsThe work is limited by the absence of experimentally derived material property data and comparative experimental results. However, the model demonstrates that the proposed microwave system would seem to be a feasible method of expediting the cure rate of polymer materials.Originality/valueThe findings of this paper will help to provide an understanding of the behaviour of thermosetting polymer materials during microwave cure processing.

Coupon Tests on z‐Pinned and Unpinned Composite Samples for Damage Resistant Applications

AbstractThe main objective of the work was to determine the mechanical properties of Z‐pinned and unpinned composites samples. Tensile and interlaminar fracture tests under mode I have been carried out on thermoset polymer matrix composite samples composed of CYTEC 977‐2 and carbon fibre yarn HTA‐12K/35. The presence of the Z‐pins has been found to significantly increase the interlaminar fracture toughness. The crack resistance improvement has been found to be accompanied by a small reduction of the in‐plane stiffness properties for a Z‐pins density of 2%. The results are presented in relation to the size and pinning quality and are rationalised on the basis of the location of Z‐pin block within the sample.

A thermo-viscoelastic analysis of process-induced residual stress in fibre-reinforced polymer–matrix composites

Process-induced residual stress in fibre-reinforced thermoset polymer–matrix composites was analysed using a thermo-viscoelastic micromechanical model and the finite element method. A three-dimensional unit cell with glass fibre and epoxy polymer–matrix, representing the periodic microstructure of unidirectional fibre-reinforced composites, was considered to compute cure residual stress of fibre composites induced by chemical shrinkage of the epoxy resin and thermal cooling contraction of the whole fibre and resin system. The constitutive behaviour of the epoxy matrix was described by a cure and temperature-dependent viscoelastic material model. Compared to an elasticity solution, a reduction in residual stress was predicted due to the stress-relaxation caused by the viscoelastic behaviour of the epoxy matrix. Calculated residual stress shows strong dependency on the fibre volume fraction and fibre packing. After the cure process is complete, residual stress tends to relax to a constant value. The effect of residual stress on damage and failure of the model was also studied using the maximum stress failure criterion combined with a post-failure stiffness reduction technique. Damage onset, in terms of the location and the load level, was shown to be clearly influenced by the residual stress for both normal and shear loading. Initial and final failure envelopes, predicted for biaxial normal (longitudinal and transverse) loading and combined shear (longitudinal) and normal (transverse) loading, were shown to be shifted and contracted by the inclusion of residual stress. For final failure, residual stress was seen to have little effect on the load levels for longitudinal failure but greatly affected the load levels for transverse and shear failure. Residual stress could be detrimental or beneficial depending on the state of existing residual stress and the loading conditions.