Post-cure Temperature Research Articles

Effect of Different Curing Catalysts on Curing Behavior of Transparent Epoxy Molding Compound for SMD LED Packaging

The transparent epoxy molding compound (EMC) for integrated circuits (IC) packaging was prepared by using tetrahydromethyl-1,3-isobenzofurandione as curing agent, respectively using 2-methyl imidazole and triphenyl phosphine as curing accelerator. The effect of curing accelerator type on curing behavior of EMC was investigated by non-isothermal DSC method in this paper. Based on Kissinger method, Crane method and Ozawa method, the kinetic parameters such as activation energy and reaction order of the curing reaction were obtained. The characteristic temperatures of the curing process such as gel temperature, curing temperature and post-curing temperature were calculated by extrapolation. The results showed that EMC with 2-methyl imidazole had a lower activation energy compared to EMC with triphenyl phosphine, which provided the basic data for the optimal recipe of EMC and the determination of IC packaging technologies.

Effect of temperature on post-cure polymerization of bulk-fill composites

ObjectivesTo investigate the 24h post-cure polymerization and the effect of temperature on the post-cure polymerization of one conventional and three bulk-fill composite materials. MethodsA conventional composite GrandioSO (GR) and three bulk-fill composites: Tetric EvoCeram Bulk Fill (TECBF), Quixfil (QF) and X-tra fil (XF) were investigated. The samples were cured for 20s with irradiance of 1090mW/cm2. Composite samples were divided into two groups: the “room-temperature” group (RT, n=5) and the “body-temperature” group (BT, n=5) and they were stored in dark at 20°C and 37°C, respectively. Measurements of degree of conversion (DC) were made immediately after curing (0h) and 24h post-cure (24h). To analyse the extent of post-cure DC increase, the DC values of 0h-RT/24h-RT and 0h-BT/24h-BT were compared. To analyse the difference in DC between RT and BT, the DC values of 0h-RT/0h-BT and 24h-RT/24h-BT were compared. ResultsDC increase 24h post-cure was significant for all composites and ranged between 6.3% and 8.2% in RT and between 12.5% and 15.7% in BT. All composites demonstrated a higher DC in 24h-BT compared to 24h-RT. The difference was statistically significant for GR, TECBF and QF. ConclusionsAll composites demonstrated a significant post-cure effect after 24h. Post-cure temperature increase from 20°C to 37°C yielded a higher post-cure DC increase. Clinical significanceDue to the temperature effect on the final DC, studies performed at composite samples at room temperature may record more inferior properties than these attained in the oral cavity.

Effect of Post Curing, Fibre Content and Resin-Hardener Mixing Ratio on the Properties of Kenaf-Aramid Hybrid Composites

Polymer composites reinforced with high strength synthetic fibres have been used for many engineering applications. Environmental and economic issues, encourage the exploration on the introduction natural-synthetic fibre hybrid composites. Mechanical properties are critical to composite performance and may due to the manufacturing process conditions. This study investigates the effect of post curing temperature, natural fibre content and resin-hardener mixing ratio on mechanical properties of kenaf-Kevlar hybrid composites. A full factorial design (23) was carried out to determine the effect these factors on the responses: flexural strength, flexural modulus and impact strength. A statistical study has been performed in order to determine the how the factors affect the responses. The study showed that post-curing temperature, kenaf content and resin-hardener mixing ratio gives significant effects on the mechanical properties of kenaf-Kevlar hybrid composites.

Effect of post-cure on adhesively bonded functionally graded joints by induction heating

Functionally graded joints with an adhesive functionally modified by induction heating confer a more uniform stress distribution along the overlap and reduce the stress concentrations located at the ends of the overlap. The adhesive stiffness varies gradually along the overlap, being maximum in the middle and minimum at the ends of the overlap. This work studies the effect of post-curing on functionally graded joints obtained by induction heating. The performance of functionally graded joints, when submitted to different post-cure temperatures, was experimentally tested. Three different post-curing conditions were considered, with temperatures above and below the glass transition temperature of the fully cured network, Tg∞. The functionally graded joints (with and without post-cure) were compared with joints cured isothermally (with and without post-cure). The cure temperature values applied to the ends and to the middle of the graded joint are the same temperatures used to cure the isothermally cured joints. Analytical modelling was used to predict the failure load and to assess the effectiveness of the graded joint concept. The functionally graded joints subjected to post-cure at low temperatures (below Tg∞) show a slight decrease of the strength and the joints cured isothermally show a slight increase of the strength. With increase of the post-cure temperature (above Tg∞) the functionally graded joints exhibit strength similar to that of the joints cured isothermally. However, even for the highest post-cure temperatures, the functionally graded joints have a slightly higher strength.

The Curing Behavior of Organosilicone Materials for Large-Power LED Packaging

The organosilicone gel material for large-power LED packaging was prepared through Si-H addition reaction of hydrogen-silicone with vinyl-silicone catalyzed by Pt coordination compound in this paper. The curing behavior was investigated by DSC method, and the curing dynamic parameters were obtained, i.e., the curing activation energy and reaction level of the system were 79.23kJ/mol and 0.8271 respectively, the initial curing temperature, maximum curing temperature and post-curing temperature were 75°C, 90°Cand 120°C, respectively, which supplied the basic data for the preparation and application of organosilicone materials for large-power LED packaging.

Effects of Curing Cycle and Thermal History on the Glass Transition Temperature of Adhesives

The glass transition temperature (T g) of a thermosetting polymer such as a structural adhesive depends on the thermal history (cure cycle) as well as the current temperature. The manner in which the T g of the adhesive changes with different cure cycles and thermal histories was studied in the present paper, after a damping at resonance method of measuring the T g of the adhesive had been developed previously by the authors. It is shown here that T g is affected by both the post-cure temperature and its duration, but is more dependent on the temperature. However, prolonged post-curing can cause a decrease in T g, and thus the appropriate temperature and duration need to be used.

Effect of Post Curing Temperature on Viscoelastic and Flexural Properties of Epoxy/Alumina Polymer Nanocomposites

In the present work, effect of post curing temperature on viscoelastic and flexural properties of epoxy/alumina polymer nanocomposite was evaluated in order to optimize the post curing temperature. Polymer nanocomposites (PNC) containing of 0.5, 1 and 1.5wt.% of rod shape alumina nanoparticles were prepared by in-situ polymerization technique. Good dispersion of nanoparticles in epoxy matrix was observed through transmission electron micrographs of nanocomposites. The curing reaction of the epoxy and nanocomposites was analyzed through Differential Scanning Calorimetry (DSC) for temperature varying from 25°C to 200°C. Temperatures 80°C, 100°C, 120°C and 150°C were selected for post curing on the basis of DSC thermographs. Dynamic mechanical analysis (DMA) tests were performed to determine the viscoelastic properties and three point bend flexural tests were conducted to evaluate the flexural properties of PNC. The results indicated that the post curing at a temperature below the glass transition temperature of epoxy enhanced the viscoelastic and flexural properties of PNC's and post curing temperature above the glass transition temperature of epoxy had a detrimental effect on the properties for both neat epoxy as well as nanocomposites. As the post curing temperature was increased the glass transition temperature increases for both the neat epoxy and nanocomposites, however the increment in glass transition temperature of PNC was more in comparison to that of neat epoxy. Flexural modulus and strength of epoxy and PNC decreased with the increase in post cure temperature.

Effects of the Preparation Parameters on the Properties of Graphite/Carbon Fiber/Copper/Phenolic Resin Composites

The polymer composites consist of phenolic resin, natural graphite, carbon fiber and copper powder, are fabricated by hot compression moulding or compression moulding followed by post-curing. The density, electrical conductivity and flexural strength of composites are analyzed to determine the influences of post-curing temperature and preparing method on the physical, electrical and mechanical properties of composites. It is found that the density, electrical conductivity and flexural strength of composites increase with increasing post-curing temperature for composites prepared by compression moulding followed by post-curing. The flexural strength is more strongly dependent on post-curing temperature. At 170 °C, the density, electrical conductivity and flexural strength of composites were 1.85 g/cm3, 2.94 × 103S/m and 40 MPa respectively. The cross-linking skeleton structure well established in the composites could be the main reason for the largely increasing of flexural strength as post-curing temperature increases. The results also show that the properties of composites prepared by hot compression moulding are higher than those of composites prepared by compression moulding followed by post-curing.

Hardness evaluation of cured urea–formaldehyde resins with different formaldehyde/urea mole ratios using nanoindentation method

To understand the influence of formaldehyde/urea (F/U) mole ratio on the properties of urea–formaldehyde (UF) resins, this study investigated hardness of cured UF resins with different F/U mole ratios using a nanoindentation method. The traditional Brinell hardness (HB) method was also used for comparison. The HB of cured UF resin films with different F/U mole ratios was determined after exposing the films to different post-curing temperatures. The nanoindentation method was employed for these films to measure Meyer hardness (HM) and reduced modulus (Er) which have been used to calculate the elastic modulus (Es) of cured UF resins. As the F/U mole ratio decreased, the HB decreased continuously, indicating a less rigid network structure in low F/U mole ratio UF resins. The higher the post-curing temperature, the greater the value of HB. The HM value also showed a similar trend as a function of F/U mole ratio. However, the Er and Es did not show a consistent trend as exhibited by HM and HB. Both HM and Er showed much greater variation in the coefficient of variation (COV) at lower F/U mole ratios 1.0 and 1.2, indicating a more heterogeneous composition of these resins. Linear relationships between HM and Er indicate that heterogeneity of the surface composition of samples contributes greatly to variations in the measured values. This variability is discussed in terms of crystal structures present in the cured UF resins of low F/U mole ratios.

Effects of postcure temperature variation on hygrothermal‐mechanical properties of an out‐of‐autoclave polymer composite

ABSTRACTThe effects of cure temperature variation on the properties of an out‐of‐autoclave polymer composite manufactured using Cycom 5320 8HS prepreg were investigated using different postcure temperatures of a two‐stage cure cycle. In addition, the effects of adverse environmental conditions on the cure temperature variation were studied by conditioning the samples in an environmental chamber until they reached moisture equilibrium. The state of cure was obtained using a differential scanning calorimeter and dynamic mechanical analyzer. The mechanical properties were obtained using short‐beam shear (SBS) and combined loading compression (CLC) test methods. The state of cure obtained showed increases in total heat of reaction, degree of cure, and glass transition temperature as the postcure temperature increased. The SBS and CLC strengths showed an increasing trend as postcure temperature increased. Good correlations were obtained between the material's cure temperatures, state of cure, and mechanical properties for room temperature dry and hot wet conditions. The study showed that the state of cure can be used to define, monitor, and verify the cure quality. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3090–3097, 2013

Viscoelastic properties and morphology of dicyanate ester/epoxy co-polymers modified with polysiloxane and butadiene–acrylonitrile rubbers

Dynamic mechanical analysis was conducted on specimens prepared from cyanate ester (CE) and epoxy (EP) resins cured together at various mass compositions. Increase of amount of epoxy resin in composition was shown to have a disadvantageous effect on glass transition temperature (Tg). It was shown that post-curing procedure was needed to produce a polymer matrix with a single glass transition relaxation, but increase in post-cure temperature up to 250 °C resulted in slight reduction in Tg for epoxy/cyanate copolymers. TG results proved that the presence of epoxy resin reduces thermal stability of the cyanate/epoxy materials. The neat CE and EP/CE systems containing 30 wt% of epoxy resin were modified using epoxy-terminated butadiene–acrylonitrile rubber (ETBN) and polysiloxane core–shell elastomer (PS). The scanning electron microscopy (SEM) results showed the existence of second phase of ETBN and PS modifiers. Only in the case of EP/CE composition modified with ETBN, well-dispersed second phase domains were observed. Analysis of SEM images for other CE- and EP/CE-modified systems revealed the formation of spherical aggregates.

Modeling Fiber Composites during the Cure Process for Piezoelectric Actuation

Analytical, numerical, and experimental modeling methods are presented to predict deformation after the cure process of thin unsymmetric laminates for piezoelectric actuation. During fabrication, laminates deform to several post-cure room temperature shapes. Thin cross-ply laminates deform to a circular cylindrical post-cure shape while thicker laminates deform to a saddle shape. Post-cure shapes are dependent on ply orientation, thickness, and material properties. Because, CLT alone does not always predict the correct post-cure room temperature shape of the thin composite laminates, an extension of CLT with the Rayleigh-Ritz technique and potential energies are used to better predict these shapes. Finite element models are used to predict the post-cure room temperature shapes. Thin composite laminates are modeled coupling heat transfer and structural mechanics, which are necessary for modeling the cure process. Modeling the fabrication process captured important data such as residual stresses from the cure process, room temperature shapes, and bi-stability of the composite laminates. To validate these analytical and numerical results, experiments were con- ducted using macro-fiber composite (MFC) patches for morphing the laminates. The experimental piezoelectric morph- ing results relate well to analytical and numerical results.

Exploratory results for composites of natural fibres mats with a natural matrix of epoxidized vegetable oils

Composites were prepared by impregnating non-woven mats of mixed natural fibres, mainly flax, hemp and a small percentage of polylactic acid, with an epoxidized soybean oil/maleic anhydride matrix resulting in a composite made up of 85% natural material. These composites comprised 65% matrix resin and 35% natural fibres and were light coloured, and had a good modulus of elasticity and modulus of rupture in the bending mode. The composites made up of 50% matrix resin and 50% natural fibres also gave good results when tested in tension. The best results appear to be obtained by using (i) higher curing temperatures (180 °C) with long post-curing times and (ii) medium temperature (150 °C) and longer press times (360 s).

Investigation of thermo-mechanical properties of adhesive used for bonding CF fabrics to concrete members using post-curing techniques

Carbon fibre reinforced polymers (CFRPs) have been increasingly employed for structural strengthening using bonding adhesives. The work in this paper reports the use of post-curing temperature on adhesive properties in CFRP/concrete systems which use a bonding adhesive under a sustained load to achieve thermal and mechanical performance. An increase in the adhesives glass transition temperature were achieved for post-curing, and as expected it was found that the improvement in the glass transition was greater for samples post-cured at high temperatures, compared to those which had only been exposed to moderately elevated temperatures. However, the single-lap shear test results at elevated temperatures under sustained loads showed a greater improvement in the bond-loss temperature compared with those which were post-cured at only moderately elevated temperatures, with higher temperatures negatively affecting the concrete properties, particularly at the adhesive/concrete interface.

Addition-curable phthalonitrile-functionalized novolac resin

A novel addition-curable novolac resin with phthalonitrile groups (PN) was successfully synthesized by a simple nucleophilic substitution reaction between the novolac resin and 4-nitrophthalonitrile. The final product was characterized with gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectrometry, and proton nuclear magnetic resonance (1H-NMR) spectroscopy. Processing capability and cure behavior of PN resin was investigated by rheometer and differential scanning calorimetry (DSC), respectively. Rheometric studies showed PN resin possessed a broad processing window between 140 and 225°C with a low viscosity from 0.4 to 4 Pa.s. DSC results showed PN resin can be cured at about 220°C via thermal polymerization of phthalonitrile groups. An ultrahigh curing temperature (such as 375°C) that was typical for the other phthalonitrile functional prepolymers was not necessary for this resin and 250°C was used as a maximum post-cure temperature to achieve the desired properties. Thermogravimetric analysis (TGA) showed T5% (temperature of 5% weight loss) of the final cured products in nitrogen was 448.7°C, and the char yield was 70.29% at 900°C. Furthermore, T5% of cured PN resin in air was 455.2°C, and the char yield in air was 34.48% at 700°C,revealing that the cured resin possessed excellent thermo-oxidative stability. Dynamic mechanical analysis (DMA) showed the inflection point of tan δ was 371.9°C. The excellent processability and thermal stabilities proved PN resin as a promising candidate for advanced composite matrices.

Low coefficient of thermal expansion of thermoset composite materials

Selection of the correct resin – filler combination is important in achieving materials which have a low coefficient of thermal expansion (CTE). A study of nanosilica-modified resin, in combination with silica fillers, allows low levels of CTE to be achieved. In this study, a novel curing agent, ytterbium triflate, is reported. This curing agent provides a stable catalyst system which can be used to create the viscous composite mixtures but has the facility of effective cure over a relatively narrow temperature range from 70 °C to 100 °C. A series of formulations were examined based on incorporation of fillers with nanoscale silica particles into either the pure resin or a resin which contained nanoscale functionalized silica particles. The filler incorporation leads to a significant increase in the glass transition temperature as determined by dynamic mechanical thermal analysis. The CTE was observed to be lower below Tg than above it. Changing the nanosilica particle size and distribution produced significant changes in the values. However, the CTE scaled according to the total silica content; and the values were in general lower than those calculated theoretically. The use of a highly functional o-cresol epoxy novolac demonstrated how increasing functionality raised the Tg and lowered the CTE, but the use of too high a post-cure temperature reversed this trend. Very good results were achieved using 3,4-epoxycyclohexylmethyl, 3,4 epoxycyclohexanecarboxylate, which has a low viscosity and allowed high levels of silica to be readily achieved. This article indicates how the adjustment of the epoxy selected to be used as the base material and the type of silica particles used allows the values of Tg and CTE to be modified in a composite material.

Preparation of photo curable highly hydrophobic coatings using a modified castor oil derivative as a sol–gel component

Modification and use of natural products have gained a lot of interest in recent years due to their environmental friendliness and their availability from different sources. In this study castor oil based photo curable highly hydrophobic coatings were prepared and characterized. Castor oil (CO) was first modified with 3-isocyanato propyl triethoxy silane and then it was hydrolyzed prior to the coating preparation. The resulting precursor was mixed with norbornyl acrylate, hexane diol diacrylate and hydrophobic coatings were prepared with the aid of fluorinated and nonfluorinated alkoxy silane coupling agents. The addition of fluorine showed a significant impact on the properties of the coatings. As the fluorine content was increased in the formulations, flame retardancy and the contact angle values of the coatings increased. The highest amount of fluorine containing coating showed a contact angle of 119°. Then with the addition of nonfluorinated alkoxysilane compounds, a contact angle of 130° was reached. Also the effect of post-cure temperature on contact angle values was investigated.

Using Taguchi experimental design to reveal the impact of parameters affecting the abrasion resistance of sol–gel based UV curable nanocomposite films on polycarbonate

This work aims at studying the abrasion resistance of differently formulated organic–inorganic hybrid coatings prepared by sol–gel method. The organic phase contained UV curable urethane acrylate oligomers and monomers having different functionalities. The inorganic phase was composed of tetraethyl orthosilicate (TEOS) and 3-methacryloxy propyltrimethoxy silane (MEMO). Through a Taguchi experimental design, the impact of influencing parameters such as molar ratio of precursors, hydrolysis ratio (R), post-curing temperature, post-curing time and weight percentage of inorganic to organic part were investigated. Very high transparency of hybrid coatings indicated that nano sized inorganic phase had formed. MEMO could facilitate the connection of two phases, preventing macro phase separation. However, high levels of MEMO lead to ‘defect structure’ in silica network as well as to decreased transparency and mechanical properties. The optimum condition in which highly transparent films with great abrasion resistance occurred was observed at equimolar ratio of water to alkoxide and TEOS: MEMO ratio being unity. Statistical analysis revealed that thermal post-curing was not significantly important.

Optimizing the Curing Process of Epoxy-Clay Nanocomposites

Epoxy resin is one of the most applied thermoset polymers as a matrix for Glass Fiber Reinforced Pipes (GFRP). Curing process of epoxy resin is important for the integrity of the GFRP. The present work has been conducted to determine the proper pre-curing and post-curing temperatures and duration to develop epoxy-clay nanocomposite. During this study a differential scanning calorimeter (DSC) was used to determine the glass transition temperature and hence the degree of curing. Several samples of epoxy were prepared at different pre-curing and post-curing temperatures and durations. Pre-curing temperatures ranging from 80 to 150°C and post-curing temperatures ranging from 150 to 200°C were studied. The results show that the optimum pre-curing and post-curing temperatures are 100 and 170°C, respectively. Regarding the effect of curing duration, several specimens were prepared at the same pre-curing and post-curing temperatures with different curing durations of 1, 2, and 3 hours. It was observed that beyond one hour curing, the changes in the Tg and the degree of crosslinking were negligible. Using these optimum conditions samples of epoxy-clay nanocomposites were prepared using ultrasonication. The results showed that the addition of nonoclay to epoxy resulted in a reduction of the Tg.

Morphological control of polymerized n-octadecylsiloxane

Polymerized n-octadecylsiloxane (PODS) was prepared by coating glass substrates with liquid ocatdecyltrichlorosilane (OTS) followed by dipping-in a solvent. The morphology control of PODS was investigated by the post curing temperature as well as the use of different solvents. The resulting substrates were characterized by scanning electron microscopy (SEM), contact angle measurements, and wide angle X-ray diffractometry (XRD). It is shown that both post curing temperature and extracting solvents affect the morphology of PODS. The temperature dependent morphology was investigated and is ascribed to the physiochemical properties of PODS. For the solvent-dependent morphology, it is proposed that the solvation capability of a solvent to OTS and the presence of a hydrophilic/hydrophobic interface are critical in the PODS morphology. This paper shows the controlling parameter and possible explanation in the crystallinity and wettability of PODS films, which may be useful to other silane-based systems.