Post-cure Temperature Research Articles

Impact of Different Post-Curing Temperatures on Mechanical and Physical Properties of Waste-Modified Polymer Composites.

One of the key trends affecting the future of the construction industry is the issue of ecology; therefore, current activities in construction aim to reduce the use of raw materials, which is made possible by including recycled materials in composites, among other methods. This article describes the results of tests conducted using four types of epoxy composites, i.e., composites modified with waste rubber (WR), composites modified with waste polyethylene (PE) agglomerate, glycolysate obtained using polyethylene terephthalate (PET) waste, and control unmodified mortars (CUM). Selected properties of the mortars were monitored during their maturation under laboratory conditions, as well as after post-curing at elevated temperatures in the range of 60 °C-180 °C. With the increase in the reheating temperature, an increase in the flexural strength of all types of mortars was noted, with the highest more than twofold stronger than the unmodified composites. The compressive strength increased up to a temperature of 140 °C, and then decreased slightly. The highest value of 139.8 MPa was obtained using PET mortars. Post-curing also led to a slight loss of mass of all samples in the range of 0 to 0.06%. Statistical methods were employed, which made it possible to determine the post-curing temperature and composite composition for which the determined properties are simultaneously the most beneficial, especially for the prefabricated elements.

Reduced warpage in semiconductor packages: Optimizing post-cure temperature profile considering cure shrinkage and viscoelasticity of epoxy molding compound

Warpage in semiconductor packages is a critical issue that affects their reliability and performance. This study aims to minimize the warpage of a bi-material dummy package by optimizing the post-mold curing (PMC) temperature profile. A warpage simulation model was developed considering the viscoelastic properties and cure shrinkage behavior of the epoxy molding compound (EMC). A compression molding monitoring system was also developed to analyze the cure behavior of the EMC. The gelation point of the EMC during compression molding was determined using a dielectric sensor, while cure shrinkage behaviors were analyzed using a fiber Bragg grating sensor. Viscoelastic properties were characterized through stress relaxation tests, and thermal properties were measured using three-dimensional digital image correlation. The developed simulation model was used to optimize the PMC temperature profile using a genetic algorithm. Experimental validation showed that the optimized temperature profile reduced the warpage from ∼1519 μm to 486 μm compared to a linear profile. The findings of this study have broader implications for the design and manufacturing of semiconductor packages, as the proposed approach can be applied to minimize warpage and improve package reliability.

Vanillin based phthalonitrile and acetylene bifunctional resins

AbstractThe renewable and biosynthetic molecule, vanillin, were used in the preparation of new phthalonitrile (PN) and ethynylbenzene (EB) bifunctional resins without pre‐modification of the vanillin structure. This PN resin was characterized by differential scanning calorimetry, thermogravimetric analysis, nuclear magnetic resonance spectroscopy, rheometry, and single crystal x‐ray diffraction. The monomers exhibited excellent rheometric viscosities below 250 Cp at processing temperatures and a good pot life. After complete curing, the PN polymers exhibited thermal stability above 500°C, a glass transition temperature (Tg) above the final postcure temperature of 380°C, and exceptional retention of structural integrity over a large temperature range. These results suggest that vanillin derived EBPN based resins are excellent candidates for use in a variety of applications where high temperature and mechanical stability is critical.

Modeling of curing and post-curing kinetics for a thermoset adhesive

The properties of adhesives cured at low temperatures are often significantly affected by post-curing effects. This paper introduces a method to model both the curing and post-curing kinetics for thermoset adhesives. The total and residual enthalpies and the glass-transition temperature (Tg) of the adhesive were measured via differential scanning calorimetry. The obtained degree of cure (DOC) and Tg were then fitted to determine their functional relationship. Low-temperature curing experiments were conducted, and an nth-order curing kinetics equation was developed through the fitting of data. Post-curing experiments were performed on samples with varying initial DOCs, and the resulting post-curing data were normalized and fitted using an nth-order model. The relationships between the kinetic parameters and the initial DOC, post-curing temperature and time were analyzed, and a comprehensive kinetics model crossing the curing and post-curing stages was successfully established. Model validation was carried out, and the results demonstrated a good predictive capability.

Effects of post-processing curing parameters and gamma irradiation on the mechanical properties of medical graded vat photopolymerization parts

Purpose This paper aims to investigate the influence of post-curing temperature, post-curing time and gamma ray irradiation dose upon the tensile and compressive mechanical properties of the medical graded vat photopolymerization parts. Design/methodology/approach Medical graded vat photopolymerization specimens, made from photopolymer resin, were fabricated using bottom-up vat photopolymerization machine. Tensile and compressive tests were conducted to assess the mechanical properties. The specimens were categorized into uncured and post-curing groups. Temperature post-processing and/or gamma irradiation exposure were for post-curing specimens. The post-curing parameters considered included temperature levels of 50°C, 60°C and 70°C, with 1, 2, 3 and 4 h periods. For the gamma irradiation, the exposure doses were 25, 50, 75 and 100 kGy. Findings Post-curing improved the mechanical properties of medical graded vat photopolymerization parts for both tensile and compressive specimens. Post-curing temperature greater than 50°C or a prolonged post-curing period of more than 1 h made insignificant changes or deterioration in mechanical properties. The optimal post-curing condition was therefore a 50°C post-curing temperature with 1 h post-curing time. Exposure to gamma ray improved the compressive mechanical properties, but deteriorated tensile mechanical properties. Higher gamma irradiation doses could decrease the mechanical properties and also make the part more brittle, especially for doses more than 25 kGy. Originality/value The obtained results would be beneficial to the medical device manufacturer who fabricated the invasive temporary contact personalized surgical instruments by vat photopolymerization technique. In addition, it also raised awareness in excessive gamma sterilization in the medical graded vat photopolymerization parts.

Post curing optimization for tensile strength of hybrid ramie-carbon fiber reinforced polymer

The optimization of post-curing processes is crucial for enhancing the performance of epoxy-based fiber-reinforced polymers (FRP) by ensuring adequate cross-linking. This study focuses on optimizing the post-curing parameters for hybrid Ramie and Carbon fiber composites with the primary objective of improving tensile strength. Variations in post-curing temperature, post-curing time, and the number of synthetic fiber layers were systematically investigated across three levels using Taguchi design of experiments. The ultimate tensile stress was employed as the response parameter. Results indicate that post-curing temperature exerts a greater influence on tensile strength compared to post-curing time. A failure pattern of natural fiber followed by synthetic fibers was seen to happen progressively. A precise multivariable regression model was developed to predict the response for different combinations of post-curing parameters. Furthermore, employing particle swarm optimization revealed an optimal post-curing time of 12 h and an optimal temperature of 60°C. These findings contribute to the optimization of post-curing processes in hybrid fiber composites, thereby enhancing their mechanical properties.

Effect of Elevated Temperature on the Lightweight Aggregate Fibre Reinforced Self-Consolidating Concrete

This study comprehensively investigates fiber-reinforced self-compacting concrete (FRSCC) behavior across multiple grade variations, namely M20, M30, and M40. The study encompasses substituting conventional natural aggregate with sintered fly ash, exploring replacement percentages of 10%, 20%, and 30%. The primary objective of this study is to identify the optimum Strength achieved through a 20% replacement ratio. The assessment of fresh properties of FRSCC was undertaken through rigorous testing protocols involving the L box, J ring, and V funnel tests, following the guidelines stipulated by the European Guidelines for Self-Compacting Concrete (EFNARC). Furthermore, the research extensively analyzed vital mechanical properties, including compressive Strength, split tensile Strength, and flexural Strength. These evaluations provided insights into the influence of sintered fly ash incorporation on the structural performance of FRSCC. The investigation extended to a post-curing temperature study, subjecting the concrete specimens to varying temperatures of 100 °C, 300 °C, 600 °C, and 900 °C, followed by exposure to a 1000 °C heating furnace for 3 hours at each designated temperature. The outcomes of this research yield valuable insights into the potential improvements in the mechanical and thermal properties of FRSCC by integrating sintered fly ash. This study is pertinent for professionals and researchers engaged in optimizing the formulation and utilization of fiber-reinforced self-compacting concrete, with implications for sustainable construction practices and enhanced resilience in diverse thermal conditions. Index Terms: Fibre reinforced lightweight self-compacting concrete, Fly Ash, Sintered fly ash Aggregate, Lightweight Sintered fly ash aggregate concrete, lightweight self-consolidating concrete, Crimped steel fiber.

Surface waviness of continuous fiber-reinforced thermosets – Experimental and numerical studies considering the viscoelasticity of the resin

This contribution aims to understand surface waviness formation during cooling and post-curing of glass fiber-reinforced plastics (GFRP). GFRP plates were manufactured by resin transfer molding (RTM). Part surface waviness is determined by tactile contour measuring at ambient temperature up to 1008 h after initial cooling. Additionally, the manufactured plates were exposed to elevated post-curing temperatures to study the influence of resins’ viscoelasticity on their surface waviness. In parallel, the curing and post-curing processes were analyzed using a cure- and temperature-dependent viscoelastic simulation model. The experimental results of this work capture the influence of the resin’s viscoelastic behavior on the surface waviness at ambient and temperatures. The numerical results show a satisfactory agreement with experimental values. Surface waviness amplitude increases up to 25 % for the applied post-curing cycle. The results of the present work underline the importance of the resin’s temperature-dependent viscoelasticity on the process-related formation of surface waviness.

Effect of Plant Oil Derived Bio-Resin and Curing Temperature on Static and Dynamic Mechanical Properties of Epoxy Network

The depletion of petrochemical resources and greater worldwide environmental consciousness has led to a growing interest in polymers made from renewable resources during the last two decades. Hence, this work has attempted to reduce the dependence on petroleum-based epoxy by partially replacing it with epoxidized castor oil (ECO). The ECO was blended with epoxy at 10, 20, and 30% and cured with amine hardener. The effect of bio-resin on tensile, flexural, impact strength and dynamic mechanical properties were investigated. Further, the result of post-curing temperature on static and dynamic properties was examined. It was found that the addition of ECO up to 30% increased the impact strength. The 20% ECO sample showed balanced stiffness to toughness property and could be considered for semi-structural composite applications. The post-curing of samples at 150 °C showed better mechanical and dynamic properties except for impact strength.

Light-settable polybenzoxazines for marine antifouling coatings

Building benzoxazine coatings on large equipment is of great practical importance and challenging. In this work, a main-chain type benzoxazine (MCBZ) resin that can be quickly shaped under UV light was successfully synthesized and can be directly coated into a film. In addition, it had a wide processing window, low curing temperature, excellent static antifouling effect, and sterilization effect. The d12-DHBP-MCBZ resin was prepared from dodecamine, which ensured the sterilization effect, and 4, 4′-dihydroxy-benzophenone provided the photoinitiation sites and activated the oxazine ring. By adjusting the ratio of d12-DHBP-MCBZ to TMPTMA, hydrophilic benzoxazine coatings can be prepared, suitable for fouling-resisting coatings. The results indicated that the d12-DHBP-MCBZ resin could be quickly shaped under UV light, and the post-curing temperature was only 140 °C. In particular, the coatings' excellent hydrophilicity can effectively prevent fouling organisms' adhesion and improve the static antifouling effect. It was worth mentioning that Poly (BZ/20 %TMA) coating achieved a high sterilization performance of >99 %. These works gave us a new strategy to solve application problems of benzoxazine coatings on large equipment and antifouling coating efficiency problems.

Computation-based design of multifunctional self-curing epoxy resin containing intensive hydrogen bond network: A novel super-strong, high reactivity and flame-retardant coating

The crosslink network of epoxy resin has a decisive influence on the overall performance, and the design of special network topologies through computer-aided methods is gaining much more attention. Based on molecular dynamics (MD) simulation and DFT calculation, a novel high-performance epoxy resin containing an amide bond has been ingeniously designed, which can be molded under heating without the addition of curing agent, thus greatly optimizes the fabrication process. The absence of curing agent significantly increases type and number of hydrogen bonds and forming an intensive hydrogen bond network, which leads to ultra-high flexural modulus up to 7026 MPa, 106 % higher than the traditional high-performance resin (AG80/DDM). The catalytic effect of the amide bond greatly improves the curing efficiency, endowing lower post-curing temperature (150 °C), and the rich catalytic sites enables rapid crosslinking of the resin to form more compact network. In addition, the abundant amide bonds impart intrinsic flame retardancy as well as increased char yield to the resin. The resin with ultra-high modulus, high curing efficiency and flame retardancy has good potential for application as protective coating and provides new ideas for the design of high-performance epoxy resins.

Effect of Post-Curing Heat Treatment on Tensile Properties of Carbon UD/Vinyl Ester Composite with VARI Manufacturing Method

In terms of enhancing the mechanical properties of the com-posite material, we investigate the effect of different post-curing tem-peratures on the tensile strength, strain, and elastic modulus of carbon UD/Vinyl Ester composite. The performance of composite material can be developed by modifying the condition of manufacture to en-hance the bonding between resin and fibre. The best interlocking will occur upon the complete polymerization reactions of the resin. It was characterized by the formation of the polymer cross-link chain. These conditions are commonly called curing conditions. We did three dif-ferent post-curing treatments for this composite, they were conditioned at room temperature (approximately 25° C), 80° C, and 100 ° C, for 24 hrs, 4 hrs, and 4 hrs time respectively. The tensile properties have al-ready been tested for both composites that refer to ASTM D3039. The Ultimate Tensile Strength (UTS) of three different heat treatment composites was increased by increasing the heat temperature from 25° C to 80°C and 100° C, the increment is about 1.17% and 17.46% ap-proximately. Furthermore, still comparing with the 25° C post-curing treatment, the modulus of elasticity value with heat treatment in 80 ° C is a little bit decreased to 7.29% but it decreased significantly for 47.42% in 100° C heat treatment.

Effect of reinforcement phases and post-cure temperature on adhesively bonded hybrid patch repair in indented glass/epoxy composite laminates

ABSTRACT This paper focuses on the experimental investigation on the effect of different fiber reinforcement phases and post-cure temperature to improve the strength recovery of adhesively bonded patch repair in glass/epoxy composite laminates. The repair was performed on the site of damaged region in the laminates by using various configurations of patches such as chopped glass (CG), chopped glass/carbon (CGC), chopped glass/kevlar (CGK), ply-by-ply glass (PG), ply-by-ply glass/carbon (PGC), ply-by-ply glass/kevlar (PGK), stitched glass (SG), stitched glass/carbon (SGC), and stitched glass/kevlar (SGK). The result reveals that the SGK hybrid patch repaired laminates offered a strength recovery by 101.5% as compared with damaged laminates. Further, the SGK hybrid patch was subjected to post-cure temperatures of 50°C, 70°C, 90°C, and 110°C which were considered based on the glass transition temperature (Tg) of glass/epoxy laminates. The result shows that the SGK hybrid patch with a post-cured temperature of 50°C has equal strength with virgin laminates and the strength recovery was improved by 112.9% as compared with damaged laminates. This study concluded that the adhesively bonded hybrid patch repair with a post-cure temperature of 50°C can be used for various fiber-reinforced polymer (FRP) industries to repair laminated composites.

A photosensitive composition based on an aromatic polyamide for LCD 4D printing of shape memory mechanically robust materials

High-temperature shape memory polymers (SMPs) draw growing interest from researchers due to their potential as materials for application in the field of high-temperature smart devices. However, in the majority of cases the processing of high-temperature SMPs is limited by fabrication of two-dimensional films. Here, we have prepared a photosensitive composition based on high-performance heat resistant poly-N,N′-(m-phenylene)isophthalamide (MPA) and photosensitive components (N,N-dimethylacrylamide and bisphenol A ethoxylate diacrylate (BAEDA)). It has been shown by IR spectroscopy, that LCD 3D printing followed by post-curing at 150 °C results in the formation of semi-interpenetrating polymer networks, while thermal processing at a temperature ≥200 °C leads to the formation of fully crosslinked structures due to the interaction of NH groups from MPA and acrylic groups from BAEDA via the Michael addition. The post-curing temperature has a significant effect on the thermal and mechanical properties of materials. Thermal post-curing of 3D printed samples at 250 °C for 1 h results in the fabrication of materials with the highest tensile strength (92.4 ± 6.1 MPa), glass transition temperature (148 °C) and thermal decomposition temperature (above 350 °C). Remarkably, MPA-based materials exhibit an excellent shape memory performance at temperatures >150 °C, with fixity ratio (Rf) of 99.7 % and recovery ratio (Rr) of 99.9 %. Moreover, we showed that the glass transition temperature decreased by no more than 1 % after γ-radiation of 200 Gy. In addition, the material maintains a high storage modulus and good shape memory performance after being irradiated, and thus has a great potential in the field of aerospace structural materials.

On the Residual Stresses and Fracture Toughness of Glass/Carbon Epoxy Composites.

The resistance to delamination in polymer composite depends on their constituents, manufacturing process, environmental factors, specimen geometry, and loading conditions. The manufacturing of laminated composites is usually carried out at an elevated temperature, which induces thermal stresses in composites mainly due to a mismatch in the coefficient of thermal expansion (CTE) of fiber and matrix. This work aims to investigate the effect of these process-induced stresses on mode-I interlaminar fracture toughness (GI) of Glass-Carbon-Epoxy (GCE) and Glass-Epoxy (GE) composites. These composites are prepared using a manual layup technique and cured under room temperature, followed by post-curing using different curing conditions. Double cantilever beam (DCB) specimens were used to determine GI experimentally. The slitting technique was used to estimate residual stresses (longitudinal and transverse direction of crack growth) inherited in cured composites and the impact of these stresses on GI was investigated. Delaminated surfaces of composites were examined using a scanning electron microscopy (SEM) to investigate the effect of post-curing on the mode-I failure mechanism. It was found that GI of both GE and GEC composites are sensitive to the state of residual stress in the laminas. The increase in the GI of laminates can also be attributed to an increase in matrix deformation and fiber–matrix interfacial bond with the increase in post-curing temperature.

The effect of layer height and post-curing temperature on the shape memory properties of smart polymers in vat photopolymerization

PurposeThe purpose of this paper is to evaluate the influence of layer thickness and post-curing temperature on shape memory properties in components manufactured by stereolithography.Design/methodology/approachLayer thicknesses of 20 and 100 µm and 22 and 45°C for post-curing temperature were selected following the design of experiments approach. Tensile and bending tests were applied for quantitative evaluation of the shape memory effect (SME). Qualitative analysis was performed using complex geometries and computed tomography as a measurement tool. Additionally, the degree of photopolymerization and glass transition temperature (Tg) were evaluated.FindingsThe tensile test resulted in fixity and recovery ratio values close to 100%. In bending, they varied between 97%–111% for fixity and 88%–95% for recovery. The layer thickness was found to have a higher influence on the SME. In complex structures, SME was dependent on geometry and less sensitive to variation in process parameters. The post-curing temperature had a higher influence on the photopolymerization and Tg. Average Tg of 77.5°C was achieved at 45°C, compared to 73.1°C at 22°C.Originality/valueIn the current state of the art in the processing of shape memory polymers with vat photopolymerization typically, the chemical composition or the thermal and deformation patterns are studied. The effect of the processing parameters is, however, not explored. This paper aims to close the research gap and facilitate the process optimization towards high fixing and recovery characteristics.

Curing Kinetics of Methylene Diphenyl Diisocyanate-Based Polyurethane Elastomers.

The curing kinetics of MDI-based polyurethane elastomers were studied by non-isothermal differential scanning calorimetry (DSC). The kinetic parameters of the reaction system were calculated by the Kissinger method. The changing activation energy was observed by the Flynn–Wall–Ozawa method and the Friedman method. The results of model free fitting showed that the curing reaction could be divided into two stages, showing a change in reaction order when α > 0.45 and a piecewise curing mechanism function of the MDI-based polyurethane elastomers reaction system was deduced by autocatalytic model. The extrapolation method was used to determine the optimum curing conditions for the system, which can accurately describe the curing process. In addition, the optimal curing conditions are when: the constant temperature curing temperature of the system is 81 °C, the curing time is 29 min, and the post-curing temperature is 203 °C.

Post curing temperature effect on mechanical characterization of jute/basalt fiber reinforced hybrid composites

Fiber-reinforced polymer composites have a fast-growing performance in many areas of engineering as a replacement for metallic materials due to their low density, low cost, specific mechanical characteristics, and lower energy consumption. The efficiency of fiber-reinforced polymer composites at high temperatures is an issue that requires to be well investigated before this type of composite can be used in important engineering fields. The aim of this study is to examine the change in mechanical properties of homogeneous and hybrid composites prepared from epoxy resin reinforced with jute fabric and basalt fabric at three diverse post-curing temperatures (50°C, 70°C, and 90°C). The vacuum- assisted resin transfer molding process was used to fabricate the laminated composites. The tensile strength and microhardness values of post- cured homogeneous and hybrid composite samples were determined by tensile tests and Vickers hardness measurements. A water absorption test was also performed to determine the water absorption capacity of the fabricated composites. After tensile testing of the fabricated structures, the effect of post-curing temperatures on the interaction of the fiber-matrix interface was investigated by scanning electron microscopy analysis. The results indicate that with increasing the post-curing temperature from 50 °C to 90 °C, an improvement of 45.48% in tensile strength and 34.65% in hardness is achieved for the hybrid composites. Moreover, the results of the water absorption test show that the increased post-curing temperature reduces the water absorption capacity of the hybrid composites by 3.53 times.

Influence of curing, post-curing and testing temperatures on mechanical properties of a structural adhesive

Structural cold-curing adhesives are widely used to strengthen Reinforced Concrete (RC) structures with Fibre Reinforced Polymers (FRPs). The performance of these adhesives, and therefore the performance of the strengthening system, may be affected by temperature, as ambient-cured structural adhesives usually have low glass transition temperature (Tg). This paper presents a comprehensive experimental investigation on the influence of temperature on mechanical properties and Tg of a structural epoxy adhesive. The experimental program was divided in four groups of specimens. In Group 1, the effect of curing and post-curing temperature on Tg of the epoxy adhesive was investigated. In Groups 2–4, the effects of testing temperature, curing temperature and post-curing temperature, respectively, on adhesive mechanical properties were studied. Experimental results confirm that curing and post-curing temperature affected Tg differently depending whether the applied temperature was below or beyond the epoxy Tg. Similar behavior was observed in the mechanical properties of the epoxy, as they showed improvements when curing process (curing and post-curing) temperature was below Tg and they were negatively affected when curing process temperature was beyond Tg. Besides, tensile and compressive mechanical properties were negatively affected by testing temperatures beyond 20 °C.

Different Curing Temperature Effects on Mechanical Properties of Jute/Glass Fiber Reinforced Hybrid Composites

In this study, the effect of different curing temperatures (60°C,80°C, and 100°C) on the mechanical characteristics of Jute and Glass fiber-based hybrid composites were analyzed mechanically, physically, and morphologically. Jute fiber fabric and glass fiber fabrics (49 gr/m² and 100 gr/m²) were used as reinforcement elements, while epoxy was utilized as ma-trix materials. A vacuum assisted resin transfer molding method (VARTM) was used as the production method. The mechanical test results were achieved by the Tensile test and Vick-ers hardness test, while morphologic images were obtained by Scanning Electron Microsco-py (SEM). Physical data was also obtained by the ignition loss test. The effects of tempera-ture and hybridization on mechanical properties of hybrid composite samples formed with jute fabric and glass fiber material with different weights per square meter at different cur-ing temperatures are given in the results. Results show that increasing post cure temperature 60°C to 80°C 3.18%-3.41% rate augment in tensile strength. It was discovered that there was a decreasement in tensile strength with an increase in temperature from 80 °C to 100 °C after curing. In the hardness test results, increasing post curing temperature had an increas-ing effect on the hardness values. SEM analysis results also supported the tensile test re-sults.