Post-cure Temperature Research Articles

3D-Printed vs. Heat-Polymerizing and Autopolymerizing Denture Base Acrylic Resins.

The aim of this work was to investigate the effect of two post-curing methods on the mechanical properties of a 3D-printed denture base material. Additionally, to compare the mechanical properties of that 3D-printed material with those of conventional autopolymerizing and a heat-cured denture base material. A resin for 3D-printing denture base (Imprimo®), a heat-polymerizing acrylic resin (Paladon® 65), and an autopolymerizing acrylic resin (Palapress®) were investigated. Flexural strength, elastic modulus, fracture toughness, work of fracture, water sorption, and water solubility were evaluated. The 3D-printed test specimens were post-cured using two different units (Imprimo Cure® and Form Cure®). The tests were carried out after both dry and 30 days water storage. Data were collected and statistically analyzed. Resin type had a significant effect on the flexural strength, elastic modulus, fracture toughness, and work of fracture (p < 0.001). The flexural strength and elastic modulus for the heat-cured polymer were significantly the highest among all investigated groups regardless of the storage condition (p < 0.001). The fracture toughness and work of fracture of the 3D-printed material were significantly the lowest (p < 0.001). The heat-cured polymer had the lowest significant water solubility (p < 0.001). The post-curing method had an impact on the flexural strength of the investigated 3D-printed denture base material. The flexural strength, elastic modulus, fracture toughness, work of fracture of the 3D-printed material were inferior to those of the heat-cured one. Increased post-curing temperature may enhance the flexural properties of resin monomers used for 3D-printing dental appliances.

The Curing Kinetics of E-Glass Fiber/Epoxy Resin Prepreg and the Bending Properties of Its Products.

The curing kinetics can influence the final macroscopic properties, particularly the three-point bending of the fiber-reinforced composite materials. In this research, the curing kinetics of commercially available glass fiber/epoxy resin prepregs were studied by non-isothermal differential scanning calorimetry (DSC). The curing kinetic parameters were obtained by fitting and the apparent activation energy Ea of the prepreg, the pre-exponent factor, and the reaction order value obtained. A phenomenological nth-order curing reaction kinetic model was established according to Kissinger equation and Crane equation. Furthermore, the optimal curing temperature of the prepregs was obtained by the T-β extrapolation method. A vacuum hot pressing technique was applied to prepare composite laminates. The pre-curing, curing, and post-curing temperatures were 116, 130, and 153 °C respectively. In addition, three-point bending was used to test the specimens’ fracture behavior, and the surface morphology was analyzed. The results show that the differences in the mechanical properties of the samples are relatively small, indicating that the process settings are reasonable.

Effects of Postcuring Temperature on the Mechanical Properties and Biocompatibility of Three-Dimensional Printed Dental Resin Material.

Three-dimensional (3D) printing is an attractive technology in dentistry. Acrylic-based 3D printed resin parts have to undergo postcuring processes to enhance their mechanical and biological properties, such as UV-light and thermal polymerization. However, no previous studies have revealed how the postcuring temperature influences the biocompatibility of the produced parts. Therefore, we postprocessed 3D printed denture teeth resin under different postcuring temperatures (40, 60 and 80 °C) for different periods (15, 30, 60, 90 and 120 min), and evaluated their flexural properties, Vickers hardness, cell cytotoxicity, cell viability, and protein adsorption. In addition, confocal laser scanning was used to assess the condition of human gingival fibroblasts. It was found that increasing the postcuring temperature significantly improved the flexural strength and cell viability. The flexural strength and cell viability were 147.48 ± 5.82 MPa (mean ± standard deviation) and 89.51 ± 7.09%, respectively, in the group cured at 80 °C for 120 min, which were higher than the values in the 40 and 60 °C groups. The cell cytotoxicity increased in the 40 °C groups and for longer cultivation time. Confocal laser scanning revealed identifiable differences in the morphology of fibroblasts. This study has confirmed that the postcuring temperature influences the final mechanical and biological properties of 3D printed resin.

The effect of post-curing temperature on mechanical properties of coconut coir fiber reinforced polyester composite

This study used post-curing training as a method of strengthening. The smoking process was a process carried out in the form of heating the specimen at a certain temperature to improve the properties possessed by the composite. The purpose of this study was to study the effect of post-curing temperature on the impact strength of coconut coir fiber composites with temperature variations of 600ºC, 700ºC, 800ºC, 900ºC, 1000ºC. Specimens were prepared using a mixing method for mixing ingredients and a hand lay-up where in the composite volume fraction is prepared according to each specimen, which is 70% polyester and 30% coconut coir fiber. Each specimen is heated for 60 minutes in a conventional oven. Average impact strength and impact energy per unit area increases with the increase in post-curing temperature due to the fact that the movement of composites as well as the reduction of holes in the composites and adhesion to one another (suturing) can improve mechanical testing. The highest strength values obtained in the specimen with an increase in T = 100°C, ie 18,509 J for the average impact energy and 0,1434 J/mm2 for impact energy per unit area average.

Deep eutectic solvent for curing of phthalonitrile resin: Lower the curing temperature but improve the properties of thermosetting

Long curing duration and high curing temperature are commonly known to restrict the application of the phthalonitrile resin. In this study, a deep eutectic solvent (DES) containing ZnCl2 and urea has been developed to improve the curing process of the resorcinol-based phthalonitrile resin (DPPh) without sacrificing the useful properties of the resin. For the molar ratio of ZnCl2 and urea as 1:1 (ZnCl2-urea (1–1)), the initial curing temperature and apparent activation energy of the system were recorded as 179.5°C and 90.1 kJ/mol, respectively, indicating a reduction of 31.2% and 39.0% as compared to the pristine ZnCl2 system. More importantly, with curing time of 6 h and post-curing temperature of 300°C, the temperature at 5% weight loss as well as glass transition temperature of the resin with DES as the curing agent were 523.1°C and 370.2°C, respectively, demonstrating a significant improvement as compared to the resin cured with ZnCl2. In addition, the satisfactory long-term oxidation stability of the resin could also be obtained by employing the new curing agent. The findings from this study open a functional pathway for facile preparation of the high-performance curing agent for the phthalonitrile resin.

Mechanical and viscoelastic properties of SiO2/epoxy nanocomposites post-cured at different temperatures

ABSTRACT Response :In this investigation, an experimental study has been carried to determine the effects of post-curing temperature (Tc) on the mechanical and viscoelastic properties of SiO2/epoxy nanocomposites. The nanocomposites were prepared through ultrasonic mixing with a dispersion of 2, 4, 6, and 8 wt.% SiO2 nanoparticles and post cured at 75, 100, 125, and 150 °‌‌C. The viscoelastic properties were determined using dynamic mechanical analysis tests. The glass transition temperature (Tg) increased with an increase in Tc for pristine epoxy and nanocomposites; however, the increase in the value of Tg for pristine epoxy is less than nanocomposites. The results show that the Tc below the Tg of pristine epoxy improves the tensile properties; however, for Tc above Tg have a detrimental effect on the properties of nanocomposites. With the increase in Tc above Tg, the fracture toughness and fracture energy decrease for nanocomposites.

Epoxy Based Blends for Additive Manufacturing by Liquid Crystal Display (LCD) Printing: The Effect of Blending and Dual Curing on Daylight Curable Resins.

Epoxy-based blends printable in a Liquid Crystal Display (LCD) printer were studied. Diglycidyl ether of bisphenol A (DGEBA) mixed with Diethyltoluene diamine (DETDA) was used due to the easy processing in liquid form at room temperature and slower reactivity until heated over 150 C. The DGEBA/DETDA resin was mixed with a commercial daylight photocurable resin used for LCD screen 3D printing. Calorimetric, dynamic mechanical and rheology testing were carried out on the resulting blends. The daylight resins showed to be thermally curable. Resin’s processability in the LCD printer was evaluated for all the blends by rheology and by 3D printing trials. The best printing conditions were determined by a speed cure test. The use of a thermal post-curing cycle after the standard photocuring in the LCD printer enhanced the glass transition temperature of the daylight resin from 45 to 137 C when post-curing temperatures up to 180 C were used. The reached a value of 174 C mixing 50 wt% of DGEBA/DETDA resin with the photocurable resin when high temperature cure cycle was used.

Study on the phthalonitrile cured via bio-tyrosine cyclic peptide: Achieving good thermal properties under low post-curing temperature

Tyrosine derived cyclic peptide (TCP) was employed to promote the curing reaction of a phthalonitrile monomer 1,3-bis(3,4-dicyanophenoxy) (3BOCN). Differential scanning calorimetry (DSC) and rheological analysis were used to study the curing behaviors of the TCP/3BOCN blend and confirmed a relatively high curing efficiency. Fourier transform infrared spectrometer (FT-IR) and two-dimensional infrared vibrational echo spectroscopy suggested the cyclic peptide reactive site was responsible for the unique curing behavior. Isoindolin, phthalocyanine and triazine were confirmed as curing products. Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) were used to measure the thermal and thermomechanical properties of the cured resin. The results firstly revealed the excellent thermal stability and high glass transition temperature (Tg) of this resin even under a moderate post-curing condition.

Development of advanced fiber‐reinforced polymer composites by polymer hybridization technique: Emphasis on cure kinetics, mechanical, and thermomechanical performance

ABSTRACTPolymer hybridization technique, consisting of an interlayer arrangement of different polymers, acts as the most economical and promising technique in augmenting the glass fiber‐reinforced polymer composite's mechanical properties. This investigation focuses on the effect of cure kinetics on the flexural behavior of glass‐polymer hybrid (GPH) composite, and also elucidates the comparative analysis on the mechanical behavior of glass‐epoxy (GE) composite, glass‐vinyl ester (GVE) composite, and GPH composite. The optimal postcuring temperature has been found to be 200°C for GPH composite among the other postcuring temperatures conducted at 140, 170, and 230°C. Among all these abovementioned composites, highest flexural strength and interlaminar shear strength properties have been recorded by the 200°C postcured GPH composite leading to 10.87 and 18.76% increment, respectively, compared with GE composite. Furthermore, thermomechanical characterization has been done to know the viscoelastic behavior of the GPH composite postcured at different temperatures using dynamic mechanical thermal analysis. The fracture morphology of flexural tested composite samples demonstrated a combination of failure modes. Relevant information on the chemical restructuring and fracture morphology of experimented composite material using Fourier‐transform infrared (FTIR) spectroscopy and Scanning electron microscopy (SEM) has also been studied.

Pultruded glass fiber reinforced brominated-epoxy composites: Dynamic mechanical and flame retardant properties

With the improvements in quality of life and better awareness about the requirement for a secure environment, fire-resistant materials have gradually attracted the world’s attention and recognition. This paper investigates a proprietary process to manufacture glass fiber (GF) reinforced brominated-epoxy (BEP) flame retardant composites through pultrusion. BEP resin is manufactured with fillers as matrices, GF as reinforcements for pultrusion. The dynamic mechanical properties (DMA) and flame retardant properties of the GF reinforced BEP composites manufactured through pultrusion have been investigated. The DMA test showed higher dynamic storage modulus [Formula: see text] and lower curve of tan [Formula: see text] of pultruded composites when the filler content, postcure temperature and postcure time increased. At the same time, the glass transition temperature [Formula: see text] of the pultruded composites were shifted to a higher temperature when the filler content, postcure temperature and postcure time increased. From the flame retardant test for UL-94 and limited oxygen index (LOI), all of the pultruded GF reinforced BEP composites as well as the BEP resin showed excellent flame retardant properties.

On the Nature of Epoxy Resin Post-Curing.

Post-curing is intended to improve strength, elevate glass transition, and reduce residual stress and outgassing in thermosets. Also, experiments indicate post-curing temperatures lead to ether crosslinks and backbone dehydration. These results informed molecular dynamics methods to represent them and compare the resulting thermomechanical effects. Diglycidyl ether of bisphenol A (DGEBA)-diamino diphenyl sulfone (DDS) systems were examined. Independent variables were resin length, stoichiometry, and reaction type (i.e., amine addition, etherification, and dehydration). Etherification affected excess epoxide systems most. These were strengthened and became strain hardening. Systems which were both etherified and dehydrated were most consistent with results of post-curing experiments. Dehydration stiffened and strengthened systems with the longer resin molecules due to their intermediate hydroxyl groups for crosslinking. Changes in the concavity of functions fit to the specific volume versus temperature were used to detect thermal transitions. Etherification generally increased transition temperatures. Dehydration resulted in more transitions.

Novolac/Phenol-Containing Phthalonitrile Blends: Curing Characteristics and Composite Mechanical Properties.

The phenol-containing phthalonitrile resin is a kind of self-curing phthalonitrile resin with high-temperature resistance and excellent properties. However, the onefold phthalonitrile resin is unattainable to cured completely, and the brittleness of the cured product is non-negligible. This paper focuses on solving the above problems by blending novolac resin into phenol-containing phthalonitrile. Under the action of abundant hydroxyl group, the initial curing temperature and gelation time at 170 °C decrease by 88 °C and 2820 s, respectively, monitored by DSC and rheological analysis. FT-IR spectra of copolymers showed that the addition of novolac increased the conversion rate of nitrile. When the novolac mass fraction is 10%, the peak of nitrile group disappears, which means the complete reaction. The mechanical test of blends composites shows that the maximum fracture strain of 10 wt% novolac addition is 122% higher than those of neat phthalonitrile composites on account of the introduction of flexible novolac chain segments. The mechanical properties are sensitive to elevated post-cured temperature; this is consistent with the result of morphological investigation using SEM. Finally, the dynamic mechanical analysis indicated that the glass transition temperature heightened with the increase of novolac content and post-curing temperature.

Effect of cure kinetics and nanomaterials on glass fiber/vinyl ester composites: An assessment on mechanical, thermal and fracture morphology

In this article, optimization of post-cure temperature for glass fiber/vinyl ester (GVE) composite at 80 °C, 110 °C and 140 °C for 6 hr, laminate fabricated by hand layup method was studied. Also, mechanical strength and glass transition temperature (Tg) of GVE composites reinforced with 0.1 wt% of various nanofillers such as carboxyl functionalized multi-walled carbon nanotube (CNT-COOH), nanoclay (surface-modified), nano alumina (Al2O3) and nano silica (SiO2) by solution processing method were investigated. Optimum properties for GVE composite were obtained at 140 °C post-cure temperature. With the addition of nanomaterials, flexural properties were improved for all the materials at specified parameters, whereas significant improvement acquired in the case of nanoclay GVE composite with a optimum flexural strength of 381.16 MPa and Tg of 102 °C was obtained. Post failure analysis of the tested samples was studied using a scanning electron microscope (SEM) at room temperature.

Optimize epoxy matrix with RSM/CCD method and influence of multi-wall carbon nanotube on mechanical properties of epoxy/polyurethane

In this research, the effect of three factors amounts of polyurethane, post-curing temperature and time on the mechanical properties of epoxy/polyurethane (EP/PU) composite have been studied. Response surface methodology (RSM) coupled with central composite design was used to optimize the mechanical properties of these composites. The optimization results also show that yield strength and Young's modulus at optimum value improved up to 23.3% and 10% compared to neat epoxy matrix. The chemical structure of the EP/PU composites were characterized by FT-Infrared (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), UV–vis diffuse reflection (DRS) and Thermogravimetric analysis (TGA), also the mechanical properties were obtained by Dynamic Mechanical Thermal Analysis (DMTA) and tensile test measurements. The FT-IR spectra indicate a very weak interaction between EP and PU. Also, the influence of multi-wall carbon nanotube (MWCNT) with different concentrations (0–0.25 wt.%) on mechanical and physical properties of EP/PU matrix was investigated. The interaction behavior of the MWCNT with EP/PU as a matrix was investigated using XRD, FT-IR and molecular dynamic (MD) simulations. Dispersion of MWCNT in the EP/PU composite was also observed using SEM. The yield strength of EP/PU/MWCNT nanocomposites increased about 59.7% with the addition of 0.15 wt.% MWCNT nanofiller.

Optimization of the Curing and Post-Curing Conditions for the Manufacturing of Partially Bio-Based Epoxy Resins with Improved Toughness.

This research deals with the influence of different curing and post-curing temperatures on the mechanical and thermomechanical properties as well as the gel time of an epoxy resin prepared by the reaction of diglycidyl ether of bisphenol A (DGEBA) with an amine hardener and a reactive diluent derived from plants at 31 wt %. The highest performance was obtained for the resins cured at moderate-to-high temperatures, that is, 80 and 90 , which additionally showed a significant reduction in the gel time. This effect was ascribed to the formation of a stronger polymer network by an extended cross-linking process of the polymer chains during the resin manufacturing. Furthermore, post-curing at either 125 or 150 yielded thermosets with higher mechanical strength and, more interestingly, improved toughness, particularly for the samples previously cured at moderate temperatures. In particular, the partially bio-based epoxy resin cured at 80 and post-cured at 150 for 1 h and 30 min, respectively, showed the most balanced performance due to the formation of a more homogeneous cross-linked structure.

Effect of Phenolic Resin on Density, Porosity, Hardness, Thermal Stability, and Friction Performance as A Binder in Non-Asbestos Organic Brake Pad

Phenolic resin is the most common resin binder used in brake pad materials. Selection of the relative amount of phenolic resin is an important to maintain structurally intact with the other ingredients of brake pad composite. In this experimental study, the effects of phenolic resin as a binder in non-asbestos organic brake pad was investigated. The brake pad composite was made using a powder metallurgy technique. Four formulations with different volume fractions 10, 15, 20, and 25 were selected. Parameters applied were 47 MPa compaction pressure, 150 °C molding temperature, and 130 °C post curing temperature with 6 hours holding time. The properties of brake pad composite were examined density, porosity, hardness, thermal stability, and friction performance (refers to SNI 09-0143-1987). The results show the increase of phenolic resin content can decrease the density, porosity, thermal stability, friction coefficient, and volume wear rate by 1%, 16.79%, 2.39%, 42.5%, 24.16%, respectively. However, the hardness increases by 19.29 %. This investigation also recommends not to select 10 and 15 volume fraction of phenolic resin due to lower resistance to mechanical stresses although the thermal stability is better than the other studied composites.

Enhanced mechanical properties at 400 °C of carbon fabric reinforced phthalonitrile composites by high temperature postcure

Phthalonitrile resins have received growing attention due to their superior thermal stability and good structural properties required for high temperature applications in aerospace industry etc. In this work, a newly developed phthalonitrile blend resin with an appropriate viscosity for autoclave processing is employed for manufacturing of high quality void-free thick composite panels using MT300 carbon fabrics. In particular, the effects of postcure temperature are systematically examined on their 400 °C mechanical properties required for high temperature structural applications. Dynamic mechanical analysis reveals that the composite postcured at the high temperature of 375 °C exhibits a high glass transition temperature over 450 °C. Mechanical testing results show that the flexural and compressive strengths at room temperature are lowered by the high temperature postcure, but their counterparts at 400 °C are obviously enhanced by the postcure. Moreover, the 400 °C interlaminar shear strength initially decreases but then increases with increasing the postcure temperature. The char retention in nitrogen at 1000 °C is 89% of its initial weight. Consequently, the newly developed phthalonitrile resin is highly promising for manufacturing of thermal resistant polymeric composites for high temperature application in aerospace industry etc. that need composites to have high temperature capabilities.

Investigation on tensile properties of epoxy/graphene nano-platelets/carboxylated nitrile butadiene rubber ternary nanocomposites using response surface methodology

In this study, the response surface methodology was used to investigate the tensile properties of epoxy/graphene nano-platelets/carboxylated nitrile butadiene rubber ternary nanocomposites. Box–Benhken method was used to design experiments for four factors consisting of graphene nano-platelets (at 0, 0.75, and 1.5 wt%), carboxylated nitrile butadiene rubber (0, 5, and 10 wt%), hardener contents (80, 90, and 100 phr), and also different post curing temperature (130, 140, and 150°C). After the samples were prepared, a tensile test was performed to obtain the tensile strength, tensile modulus, and elongation at break of nanocomposites. Moreover, field-emission scanning electron microscopy was used to observe the state of graphene nano-platelets dispersion. The results obtained from the tensile tests showed that increasing the graphene nano-platelets, carboxylated nitrile butadiene rubber, and hardener contents and high post curing temperature reduced the tensile strength. The optimum value of tensile modulus was achieved at low concentration of carboxylated nitrile butadiene rubber and high contents of graphene nano-platelets, whereas maximum elongation at break occurred at high content of carboxylated nitrile butadiene rubber and low concentration of graphene nano-platelets and hardener. In addition, a second-order polynomial model was used to correlate the tensile properties of ternary nanocomposites to the desired factors. Finally, contour plots were used to determine optimum values of the desired factors. It was seen that the presence of 10 wt% of carboxylated nitrile butadiene rubber in the epoxy matrix increased the elongation at break by the considerable amount of ∼49%.

Time-dependent changes of mechanical properties of polymer-based composite materials for adhesive anchor systems

The long-term performance of adhesive anchor systems is largely determined by the time-dependent mechanical properties. As polymer-based composite materials, the properties of adhesives change during their service life dependent on environmental factors. Therefore, the influence of aging time on Young’s modulus and tensile strength of two different industrially produced materials (epoxy, vinylester) with a high filler content (20–50 vol%) were investigated considering that most literature is focused on neat resins. Mechanical properties of the vinylester based material increased with time and curing temperature. While the strength of the epoxy system increased at higher post-curing temperatures, the modulus slightly decreased, which is in contrast to most literature studies and interpreted as relaxation effect. Changes in the weight of the specimens were monitored. In contrast to other hydrolytic aging studies on submerged specimens a comparably low amount of moisture absorption of the epoxy was found when aged under realistic conditions and desorption of water of the vinylester was observed, which is an uncommon behavior. The reactivity of cement as a filler material was studied by X-ray diffraction (XRD), revealing inert cement phases even at higher temperatures and the presence of water. The results are discussed and compared to available data from literature.

Dynamic postpolymerization of 3D‐printed photopolymer nanocomposites: Effect of cellulose nanocrystal and postcure temperature

ABSTRACTCellulose nanocrystal (CNC) reinforced methacrylate (MA) resin nanocomposite was prepared by 3D stereolithography printing. A postcure process, where the printed nanocomposite was heat‐treated under different temperatures, was applied to improve the property of the printed nanocomposites. To investigate the effect of CNC and postcure temperature on the kinetic behavior of the postpolymerization of printed nanocomposites, Fourier‐transform infrared spectroscopy and differential scanning calorimetry measurement of the printed nanocomposites before and after postcure were analyzed. The postpolymerization of MA nanocomposites was promoted at a postcure temperature of 140 °C for the printed 0.5% CNC/MA nanocomposites compared to the printed MA resin. The addition of CNC retarded the polymerization of MA resin during 3D printing, resulting in poorer mechanical properties of the printed nanocomposites compared to the printed MA resin. However, after postcure, the mechanical properties of the printed nanocomposites were improved by the postpolymerization of the MA nanocomposites. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 935–946