Composites Of Resin Research Articles

Hybrid composites of epoxy resin modified with carboxyl terminated butadiene acrilonitrile copolymer and fly ash microspheres

Hybrid composites were prepared using epoxy resin (ER), carboxyl-terminated butadiene acrylonitrile copolymer (CTBN) and fly ash microspheres (mean particle size 123 μm), in different proportions. The mechanical properties of the composites were evaluated and the microstructure was investigated through scanning electronic microscopy (SEM). The results showed that the impact resistance of CTBN-modified ER was superior to that of the pure epoxy resin. For the hybrid composites with fly ash, an improvement of the impact properties was noticed only when CTBN was added.

Thermal and mechanical properties of glass reinforced soy-based polyurethane composites

Two series of polyurethane resins were prepared using Soypolyol 204 derived from soybean oil and petrochemical polyol Jeffol G30-650. Polyurethanes from soybean oil have good thermal, oxidative and weather stability, and can be used as a matrix in composite materials. The objective of this study was to compare the mechanical properties of untreated E-glass fiber reinforced composites prepared with soybean oil-based polyurethanes to that of the petrochemical polyol based ones. The effect of the polyurethane resin on physical and mechanical properties was studied. The results showed that mechanical properties such as tensile and flexural strength, tensile and flexural modulus of the Soypolyol based composites were comparable with those from composites based on petrochemical polyol. Since soy-based polyurethanes offer better thermal, oxidative and hydrolytic stability than petrochemical based ones, they could be a viable alternative to the petrochemical urethane matrix resins for composites.

Sugar cane bagasse and curaua lignins oxidized by chlorine dioxide and reacted with furfuryl alcohol: characterization and stability

Sugar cane bagasse and curaua acidolysis lignins were used to get a better understanding of the mechanism involved in a new chemical modification of sugar cane bagasse and curaua fibres, consisting in a selective oxidation of lignin by chlorine dioxide and reacting some of the created unsaturated units (quinones or muconic derivatives) with furfuryl alcohol (FA). The objective of the treatment was to create a fibre coating increasing compatibility between fibres and phenolic resins in composites. The lignins were reacted with chlorine dioxide to oxidize the phenolic units of the polymer and then treated with furfuryl alcohol. Weight percent gain of 14% and 10% were obtained for sugar cane bagasse and curaua, respectively. 1H and 31P NMR, as well as FT-IR results showed that bagasse lignin had more guaiacyl than syringyl units and the reverse for curaua lignin. 1H NMR of oxidized lignins revealed a decrease of the aromatic and methoxy content after the ClO 2 oxidation, due to partial degradation of the macromolecule. Thermal analysis showed that sugar cane lignin decomposes at lower temperature than curaua lignin, partly due to the high content of condensed structural units present in curaua lignin. Condensed units decompose at higher temperatures than uncondensed ones. The reaction of oxidized lignin with FA shifted the decomposition exotherm to lower temperature for both curaua and sugar cane bagasse lignins, due to the modification introduced into their structures.

Evaluation of a.c. conductivity behaviour of graphite filled polysulphide modified epoxy composites

Composites of epoxy resin having different amounts of graphite particles have been prepared by solution casting method. Temperature dependence of dielectric constant, tan δ and a.c. conductivity was measured in the frequency range, 1–20 kHz, temperature range, 40–180°C for 0.99, 1.96 and 2.91 wt% graphite filled and unfilled epoxy composites. It was observed that the dielectric constant, tanδ and a.c. conductivity increase with increasing temperature. Near the transition temperature the materials show anomalous behaviour for the observed properties. Peaks of dielectric constant, tan δ and a.c. conductivity were observed to shift towards lower temperature with increasing frequency. Clear relaxation (tan δ) peaks around 169°C were observed in epoxy resin, which shifted to lower temperature side on increasing the frequency. Addition of 2.91 wt% graphite shifted the tan δ peaks towards higher temperature side by creating hindrances to the rotation of polymer dipoles. Addition of 2–91 wt% graphite leads to an increased relaxation time τ of dipoles in polysulphide epoxy from 1.44 × 10−5− 3.92 × 10−5 (s) at 90°C by creating the hindrance to the rotation of dipoles.

Characterisation of a phenolic resin and sugar cane pulp composite

Polymeric materials are increasingly replacing metallic materials as a result of their properties. In this work a composite of phenolic resin and sugar cane pulp was developed. The sugar cane pulp has been previously alkalinised, dried, and milled and the particles had been classified in a range of grain sizes. Experimental assays were performed, varying the proportion of the resin and the reinforcement and the size of the cane pulp fibre, keeping the pressure and moulding temperature constant. These composites were characterised according to physical and chemical properties, through test bodies produced in moulds according to ASTM standards. The experiments performed showed that the use of sugar cane pulp as reinforcement in polymeric composites represents an option for reducing costs in industrial applications, thus suggesting a significant industrial applicability of the product.

Temperature dependence of effective thermal conductivity and thermal diffusivity of treated and untreated polymer composites

AbstractThermal properties, such as thermal conductivity, thermal diffusivity, and specific heat, of treated and untreated oil palm fiber–reinforced PF composites were measured simultaneously at room temperature and normal pressure using the transient plane source (TPS) technique. An increase in thermal conductivity was observed in the fiber‐treated and resin‐treated composites. Surface modifications of fibers by prealkali, potassium permanganate, and peroxide treatments increased the fiber–matrix adhesion by increasing porosity and pore size of the fiber surfaces. The increase in crosslinking enhanced the thermal conductivity of a composite of resin treated with peroxide compared to other composites. Also an attempt was made to explain the temperature dependence of thermal conductivity and thermal diffusivity of amorphous polymer samples using the same technique. It was observed that at the glass‐transition peak of the polymer, thermal conductivity and diffusivity were maximum. Below and above this temperature their values decreased. This has been explained on the basis of predominant scattering processes. An empirical relationship was established for the theoretical prediction of thermal conductivity and diffusivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1708–1714, 2003

Dynamic mechanical properties and interphase fiber/matrix evaluation of unidirectional glass fiber/epoxy composites

Storage modulus, loss modulus, and loss factor of unidirectional fiber composites of epoxy resin with glass fiber were determined with a Perkin Elmer DMA-7 equipment in three point bending mode. The fibers were coated with two different types of epoxy resins and the relationship between the thickness of coating and the composite viscoelastic properties were determined. A simple micromechanical model was used to analyze the data.

Analysis of simultaneous influence of operating variables on abrasive wear of phenolic composites

The paper deals with the abrasive wear investigations on various composites of phenolic resin filled with alumina powder and abraded against silicon carbide paper under dry and single pass condition. The data analysis was done using orthogonal experimental design method. The objective was to study the influence of variables such as filler concentration, load, sliding speed and abrading particle size on the abrasive wear performance of phenol-formaldehyde-based composites. Regression analysis of the data was carried out to develop equations for the composites in which the wear volumes of the specimens were expressed in terms of simultaneous contribution from the influence of load, abrading particle size, sliding speed and their mutual interactions. It was confirmed that among these factors load was the factor contributing most strongly to the wear of these composites. Sliding speed seemed to have least effect on the wear performance in the selected operating conditions. Worn surfaces were studied by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) to have an insight into the wear mechanisms and particle dispersion in the bulk of the composites.

Glass Fiber Reinforced Composites of Coloured Epoxy Resin Cured with Different Amines

A novel coloured epoxy resin has been synthesized by reaction between epichlorohydrin and bisazodiol. The curing of the resin, blended with a DGEBA resin, were characterized by differential scanning calorimetry (DSC). The thermal stability of the cured products has been investigated by thermogravimetric analysis (TGA). The cured products showed good thermal stability. Glass fibre composites were fabricated by blending a DGEBA resin and the novel coloured epoxy resin and their mechanical properties, electrical properties and chemical resistance were studied.

Electrical conductivity of carbon fibres/polyester resin composites in the percolation threshold region

The electrical conductivity of composites of a polyester resin filled with short carbon fibres has been investigated with a special attention to the properties in the percolation threshold region. A very low percolation threshold (0.7–0.8 vol% of the filler) was confirmed. In contrast to S-shaped curves calculated according to the percolation theory of composites of globular particles, the experimental conductivity vs. fibre content dependence, after a steep increase in the percolation region, increased almost linearly. This atypical behaviour was explained by a different mechanism of formation of fibrous and globular conducting structures above the percolation threshold. An increase in scatter of conductivity values observed at percolation threshold as a consequence of great fluctuation of fibre arrangement manifested itself also in the conductivity–temperature dependences.

Development of reworkable underfill from hybrid composite of free radical polymerization system and epoxy resin

The application of the underfill encapsulant is to enhance the solder joint fatigue life in the flip chip assembly, typically up to an order of magnitude, as compared to the nonunderfilled devices. Most of the current underfills, however, are primarily thermosetting epoxy resin curing system based materials, which transform into an infusible three dimensional network structure, and exhibit appreciable adhesion and reliability, but lack of desirable reworkability after curing. From the standpoint of polymeric material chemistry, other thermoplastic or thermosetting polymer materials could be of great economic/cost interest as encapsulants for some microelectronic packaging applications. In this paper, the experimental focus was devoted to the study of adhesion, reliability and reworkability of the free radical polymerization (FRP) system, as well as its hybrid composites or blends with phenoxy resin or epoxy resin (EPR), which could be potential underfill materials. The study encompassed formulation screening based on adhesion measurement, and assessment on reliability and reworkability performance for selected compositions developed so far.

Electrical relaxations in polymeric particulate composites of epoxy resin and metal particles

Abstract Composites of epoxy resins and nickel particles in various amounts were prepared and their dielectric spectra were measured in the frequency range 5 Hz–13 MHz and temperature interval from ambient to 140°C. The formalism of electric modulus proved to be efficient in analysing and interpreting obtained data. For these composites two relaxation processes are revealed in the frequency range and temperature interval of the measurements. One is an interfacial dielectric relaxation (Maxwell–Wagner–Sillars), MWS and the other is a conductivity relaxation. They both follow the Cole–Davidson approach with the exponent γ reflecting a distribution of relaxation times with the characteristics of each process. AC conductivity of these composites is frequency and temperature dependant, it generally follows the exponential law σ ac ∼ ω s and reveals a conductivity relaxation process, in the low frequencies.

Reasons for replacement and the age of failed restorations in posterior teeth of young Finnish adults

Using dentist characteristics, our aim was to evaluate the reasons for replacements of fillings, the age of failed restorations in the posterior teeth of young adults, and replacement rates. Altogether 205 patient records from the Public Oral Health Service of the City of Vantaa, Finland were evaluated. Patient age was restricted to between 25 and 30 years and type of tooth to posterior teeth only (third molars excluded). Information collected from the records included the patient's date of birth, latest DMFS and DMF, and the code for background data on the dentist. Details of each filled premolar and molar included the restorative material, location, and surface coverage of filling(s). The age of replacement of filling in premolar(s) or molar(s) was screened retrospectively from patient records. The total number of filled premolars and molars was 1873, with 1969 fillings. Forty percent of the patients had undergone replacement of filling in premolar(s) or molar(s). In all, 140 replacements had been made, accounting for 6.9% of amalgam fillings and 8.5% of tooth-colored fillings. Secondary caries, along with fractures, overhangs, and marginal discrepancy, was the most common reason for replacement. The mean age of failed amalgam fillings was 8.9 years (SD 5.2) and of failed tooth-colored fillings 2.4 years (SD 1.6). In the public sector, female dentists form the majority and their replacement rate for amalgam fillings was twice that of male dentists (7.6% vs 3.2%; P = 0.01).

Adsorption of CO2 on Composites of Strong and Weak Basic Anion Exchange Resin and Chitosan.

A new method is proposed to improve the adsorption properties of basic, macroreticular (MR) anion exchange resins by forming a material composite with chitosan. In this study, one strong basic and one weak basic MR resins were used as matrixes for the new composites. Chitosan was accumulated in the macropores of the resins, and breakthrough curves for adsorption of CO2 on the new adsorbents were measured. The resulting equilibrium and kinetic data were compared with those of the original resins. The composite of strong basic MR resin and chitosan showed a more than three times higher adsorption capacity for CO2 than the pure resin. On the other hand, the mass transport in the adsorbent slowed down due to a narrowing of the pores by deposited chitosan.

Estudo das Propriedades de Compósitos de Polianilina e Resina Epoxídica

Compósitos condutores de eletricidade envolvendo polianilina e resina epoxídica foram preparados utilizando-se o método da polimerização in situ. O método consiste da polimerização em emulsão da anilina na presença da resina epoxídica. Ácido dodecilbenzenossulfônico foi utilizado como agente dopante, que age também como surfactante da polimerização em emulsão. A condutividade elétrica do sistema Pani/resina epoxídica alcançou valores tão altos quanto 2 x 10-3 S/cm, com uma concentração de Pani correspondente a 7% em peso. O conteúdo de Pani na mistura foi determinado por análise elementar. O efeito do método de cura da resina epoxídica na condutividade elétrica, temperatura de transição vítrea e propriedades mecânicas do sistema foi também investigado.

Effect of structure on thermal behaviour of phosphorus containing addition polyimides and epoxy resins

Addition polyimides, [e.g. endo-5-norbornene-2.3-dicarboximide(nadimides), maleimides etc.] and epoxy resins have been used extensively in the past as matrix resins for advanced fiber-reinforced composites. However, inadequate flame resistance and thermal stability of these resins is one of their serious limitations. Our earlier studies have shown excellent flame resistance properties of addition polyimides based on bis(3-aminophenyl) methyl phosphine oxide (B) or tris(3-aminophenyl) phosphine oxide (T). Carbon fiber reinforced composites based on such matrix resin did not burn even in pure oxygen. In order to investigate the effect of weight percent of phosphorus on thermal behaviour and flame resistance, a series of addition polyimides and epoxy resins were prepared using B, T and amide-amines. The effect of structure on curing behaviour of resins and thermal and flame resistance of cured resins was evaluated. The results demonstrate an improvement in char yield of resins containing higher weight percent of phosphorus.

Novel Propargylether-Terminated Ester-Imide Prepolymers: III. Thermoset/thermoset blend prepolymers as matrix resins for composites

Glass-cloth-reinforced composites were prepared from prepolymers of various weight ratio blends of the state-of-the-art propargylether-terminated ester-imide (1) and bismaleimide (MB-8000). The Tg of a composite is directly related to the weight ratio of MB-8000 present. The composites demonstrated excellent initial mechanical properties. The chemical and electrical properties under severe long-ageing conditions were demonstrated.

Nd:YAG laser effects on the microleakage of composite resin restorations.

This study evaluated microleakage of composite restorations submitted to marginal treatment with Nd:YAG laser and surface sealant. Previous studies have demonstrated that Nd:YAG-lased enamel melted and became recrystallized with a morphologic appearance similar to lava, and has been used clinically in the sealing of enamel pits and fissures. Class V cavities in enamel of human premolars were restored with composite resin (Z100, 3M) and randomly divided in six groups: G1, control; G2, surface sealant marginal treatment; G3 to G6, were treated with pulsed Nd:YAG laser (1.064 microm) marginal treatment, contact fiberoptic (300 microm), air cooling, for 30 seconds, powers of 1.2-2 W, repetition rates of 20-30 Hz, energies of 40-100 mJ. Teeth were impermeabilized, immersed in a rhodamine dye, sectioned, and evaluated under stereomicroscope microscopy with scores. There were significant differences between marginal treatments; there were no differences between groups 1, 2, and 4, and 3,5, and 6; lower values of microleakage were at groups 3, 5, and 6 (Kruskal-Wallis,p = 0.05). Nd:YAG laser showed improved marginal sealing and decreased microleakage of composite resins restorations.

Water-tolerant catalysis of a silica composite of a sulfonic acid resin, Aciplex

A silica composite of a perfluorocarbonsulfonic acid resin, Aciplex, has been used as a solid acid catalyst for a variety of reactions concerning water. The Aciplex–SiO 2 composite containing 20 wt% Aciplex has a surface area of 1.3 m 2 g −1 and possesses an ion-exchanged capacity of 0.46 meq. g −1 after pretreatment at 423 K, which is higher than that of 13 wt% Nafion–SiO 2 (0.12 meq. g −1). The acid strengths estimated from an initial heat of adsorption of NH 3 were similar for these polymer resin composites. It was found that the Aciplex–SiO 2 was more active than typical solid acids such as Cs 2.5H 0.5PW 12O 40, H-ZSM-5, and SO 4 2−/ZrO 2 for hydrolysis of ethyl acetate in excess water and esterification of acrylic acid with 1-butanol, while it was less active than Cs 2.5H 0.5PW 12O 40 for N-alkylation of acrylonitrile with 1-adamantanol and solid–solid hydrolysis of 2-naphthyl acetate. The Aciplex–SiO 2 was superior in activity to Nafion–SiO 2 for all the above reactions and in thermal stability. These results indicate that Aciplex–SiO 2 is a promising solid acid catalyst for reactions involving liquid phase water.

Computer modelling and chemical kinetics of the cure of aerospace resin systems

The authors are experienced researchers in the selection, evaluation and simulation of polymeric matrix resins for advanced composites. This article reviews the current state‐of‐the‐art in cure monitoring techniques and the application of modern computational methods to determine the kinetics of cure in commonly used aerospace systems. Extensive reference is made to primary sources and conclusions drawn about the possible future developments that may evolve in this area of interest.