Curing Peak Temperature Research Articles

Influence of synthesis method and melamine content of urea-melamine-formaldehyde resins to their features in cohesion, interphase, and adhesion performance

This study investigated impacts of the synthesis method and melamine content of urea-melamine-formaldehyde (UMF) resins to their cohesive and interphase features, and adhesion in bonding wood products. Melamine at three addition levels was simultaneously reacted with urea and formaldehyde to obtain melamine-urea-formaldehyde (MUF) resins, while melamine at the same levels was initially reacted with formaldehyde and then with urea to prepare melamine-formaldehyde-urea (MFU) resins. As the melamine content increased, molecular weights, curing peak temperature, activation energy, bond-line thickness, E′max, and adhesion strength of wood products increased. These results indicated that the cohesive features of these resins mainly affected the adhesion strength in wood products while the interphase features had a partial contribution to the adhesion.

Development of amine-based latent accelerator for one-pot epoxy system with low curing temperature and high shelf life

One-pot epoxy system is widely used in prepreg applications. Achieving a long storage life and at the same time, a low curing temperature is a real challenge in one-pot systems. To deal with these challenges, we developed adducts as latent accelerators for one-pot epoxy/dicyandiamide system through the addition reaction of epoxy, phthalic anhydride and different types of alkanolamine/phenol amines. Fourier transform infrared spectroscopy (FTIR), 13C nuclear magnetic resonance spectroscopy (NMR) and thermogravimetric analysis (TGA) showed that the so-prepared adducts were long chain tertiary amines. Non-isothermal differential scanning calorimetry (DSC) proved the effectiveness of adducts towards significant reduction of the curing peak temperature of epoxy/dicyandiamide. The analysis of variance (ANOVA) revealed that the acceleration capacity is controlled by adduct ingredients of amine type, amine and phthalic anhydride content. The activation energies (Eα) projected by isoconversional methods revealed different Eα-conversion profiles for each system that were in agreement with chemorheological results. According to Málek method, Šesták–Berggren model was the most appropriate to fit the experimental reaction rates. Furthermore, for all one-pot epoxy/dicyandiamide samples, no viscosity build-up and epoxide group consumption were detected after 4 months indicating for their relatively long shelf lives.

Copolymerization of mono and difunctional benzoxazine monomers with bio-based phthalonitrile monomer: Curing behaviour, thermal, and mechanical properties

The eugenol based phthalonitrile (EPN) monomer was successfully copolymerized with mono and difunctional benzoxazine (P-a and BA-a) monomers via concerted catalysis polymerization. The loading of EPN in benzoxazine monomers was varied from 10 to 40 wt% and impacts of loading on thermal, thermomechanical and mechanical properties were studied. The FTIR analysis confirmed that both poly(P-a/EPN) and poly(BA-a/EPN) copolymers can be completely cured without the addition of curing additive. The addition of the bio-based EPN monomer enhanced the curing peak temperatures and reduced the curing reaction enthalpies. Initially, OH groups were produced from the oxazine ring opening polymerization of benzoxazine and they enhanced the curing of EPN. The thermal stabilities, as well as the stiffness and Tg of the copolymers, were much higher as compared to the neat polymers. Highest values were seen on the 40 wt% loading of EPN monomer in the copolymers. Moreover, the difunctional benzoxazine based copolymer showed higher enhancements in the properties as compared to the mono-functional benzoxazine based copolymer. The decline was seen in the flexural properties as EPN monomer contains the flexible chain in the structure. The morphological changes supported all the claims for the copolymers. The prepared copolymers can be used as a high performance thermosetting resin.

Walnut Meal as Formaldehyde-free Adhesive for Plywood Panels

Walnut meal and polyethyleneimine (PEI) were used as raw materials for producing an environmentally friendly adhesive to bond plywood, and the shear strength was investigated. The results showed that the walnut meal-based mixture adhesive can successfully be used for the production of plywood. However, the shear strength of plywood clearly changed with different raw materials ratios. Both the wet and hot water strength were improved with increasing polyethyleneimine (PEI) content. This indicated that PEI had an important contribution to the water-resistance of the mixture system, and considering the cost of PEI, a walnut meal powder and PEI weight ratio of 70:30 was recommended. The effects of walnut protein solution thermal processing time and temperature were also studied. It was beneficial to enhance the wet and hot water shear strength of plywood to increase the thermal processing time and temperature. The investigation of curing characteristic of mixture system and monomer ingredient via differential scanning calorimetry (DSC) revealed that the curing peak temperature of the mixture system was similar to PEI, and that a chemical reaction should be made between them during the heating process. Lastly, the thermal characteristic of the mixture system was investigated via thermogravimetric (TG) analysis, where good thermal resistance was displayed.

A novel ultra low-k nanocomposites of benzoxazinyl modified polyhedral oligomeric silsesquioxane and cyanate ester

Benzoxazinyl modified polyhedral oligomeric silsesquioxane (BZPOSS) is successfully synthesized and used to prepare nanocomposites with bisphenol A cyanate ester (BADCy). The DSC results showed that the curing peak temperature of BZPOSS/BADCy blend decrease significantly from 317.1 °C to 160.3 °C, suggesting the high catalytic activity of BZPOSS to the polymerization of cyanate ester. The SEM micrographs of poly(BZPOSS/BADCy) and Silicon element distribution maps given by EDS both indicated that BZPOSS disperses evenly in BADCy. Dielectric properties tests showed that the dielectric constant can be reduced by the introduction of BZPOSS, which is attributed to the nano-pores from the cage structure of POSS. When 15 wt% BZPOSS was added, the dielectric constant decreased to 2.01 and the dielectric loss was also only 0.0070 at 1 MHz. Meanwhile, DMA and TGA result showed that the thermal stability and heat resistance of poly(BZPOSS/BADCy) at high temperature decreased with increasing BZPOSS, which is due to the change of crosslinking structure of the copolymers. The influences of the crosslinking structure and the nano-porous organic-inorganic hybrid particles on the dielectric and thermal property of poly(BZPOSS/BADCy) were also discussed.

SEM Analysis of Composites with TCP/HA/Chitosan/Poly (Methylmethacrilate)

Modified cement composites were prepared by dispersing commercially available PMMA powders and chitosan/ tricalcium phosphate (TCP) or chitosan / hydroxyapatite (HA) fillers into a PMMA matrix. SEM and EDX were used to determine the compounds and the morphology of the composite. The characteristics of these materials indicate that the addition of chitosan/TCP and chitosan /HA as a constituent into the PMMA cement significantly decreases the curing peak temperature. Furthermore, the setting time increases from 4 min to 7 min, as compared to the PMMA cement. These changes could be beneficial for the handling of the bone cement paste and causing less damage to the surrounding tissues.

Effect of microfibrillated cellulose addition on thermal properties of three grades of urea-formaldehyde resin

Three grades of liquid urea-formaldehyde (UF) resin with different formaldehyde emission levels such as super E0 (SE0), E0 and E1 were modified by adding different amounts of microfibrillated cellulose (5wt% MFC and 95wt% water) that had been isolated by mechanical disintegration of pulp fibers. Thermal properties of these UF resins were investigated to understand thermal curing and degradation behaviors of the modified UF resins, using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The DSC thermograms showed an exothermic curing reaction, and the curing peak temperature of modified UF resins heavily depended on the emission resin grade with an increasing order from E1, E0 to SE0. The addition of MFC suspension into the UF resins gradually increased curing peak temperature suggesting a decrease in the resin reactivity. TGA results showed three main thermal degradation temperatures for the modified UF resins except the SE0 UF resin, which had four degradation temperatures.

Study on catalysis effect of TEPB on the curing reaction of HTPB binder system

The catalysis effect of tri (exhoxyphenyl) bismuthine (TEPB) on the curing reaction of HTPB binder system was studied by using DSC method. The curing peak temperatures of the catalyst systems were measured to calculate kinetic parameters by using Kissinger and Crane methods, respectively. Two curing reaction kinetic equations were established. The results show that TEPB has high catalytic activity and can decrease the curing temperature of HTPB binder system, down to 35 °C, in which the optimum volume of TEPB is 0.5% of HTPB binder system.

Preparation, thermal cure and ceramization of liquid precursors of SiC–ZrC

Liquid PEPSI–PZO, as precursor of SiC–ZrC multi-component ceramic, was prepared by facile reactive blending method, using phenylethynylpolysilane (PEPSI) as silicon and carbon source and polyzirconoxanesal (PZO) as zirconium source. The processing capability of PEPSI–PZO met the demands of Precursor-infiltration–pyrolysis technique (PIP) in ceramic composites fabrication. The thermal cure was realized at 130–330°C by ethynyl polymerization and condensations. The thermal cure of PEPSI–PZO precursor was promoted by catalyst Ni(acac)2, and the curing initiation and curing peak temperatures decreased by 25 and 70°C, respectively. Evidenced by ceramic yields and XRD results, the thermal pyrolysis was catalyzed by Ni(acac)2, (ceramic yield was improved by 5–10%). XRD and SEM-EDS results showed that SiC–ZrC by 1600°C pyrolysis was highly crystalline, due to the occurrence of carbothermal reduction reaction. The liquid precursor of SiC–ZrC is an ideal candidate of low cost precursors for high-temperature ceramics and ceramic matrix composites.

Adhesives formulated from bark bio-crude and phenol formaldehyde resole

Rather than replacing phenol in the synthesis of PF resole, bark-derived bio-crudes were used as an adhesive constituent by simply formulation with neat PF adhesive in this study. Bio-crude derived from white birch bark (WBB)—a typical hardwood bark and white spruce bark (WSP)—a typical softwood bark were blended with neat PF adhesive to prepare bark bio-crude formulated bio-phenol formaldehyde (BPF) adhesive (designated as bio-crude formulated BPF adhesive). It was discovered that the viable formulation ratio between bark bio-crude and neat PF adhesive depended on the bark species. WBB bio-crude could be formulated with neat PF adhesive at a formulation ratio of 50:50 (wt/wt), while WSP bio-crude can be formulated with neat PF adhesive at a higher formulation ratio up to 75:25 (wt/wt). The peak curing temperatures of the bio-crude formulated BPF adhesives were lower than that of neat PF adhesive. Activation energy for the curing of WBB bio-crude formulated BPF adhesives was higher than that for the curing of neat PF adhesive, while WSP bio-crude formulated BPF adhesive required less activation energy for curing than neat PF adhesive. Condensation between bio-crude and neat PF adhesive occured during the pre-curing process at 125°C and was confirmed by FTIR spectra. Interestingly, the introduction of bio-crude enhanced the thermal stability of the bio-crude formulated BPF adhesives at low temperatures, but as expected, thermal stability of the bio-crude formulated BPF adhesives reduced at higher temperatures and a higher formulation ratio led to lower thermal stability. At a same formulation ratio, WSP bio-crude formulated BPF adhesives showed better thermal stability than WBB bio-crude. More interestingly, the free formaldehyde emission level of 3-ply plywood bonded by bio-crude formulated BPF adhesives, in particular with the WSP bio-crude, was lower than that of the neat PF adhesive bonded plywood. Free formaldehyde emission levels from 3-ply plywood bonded with WSP bio-crude formulated BPF adhesives at the formulation ratios of 50:50 (wt/wt) and 75:25 (wt/wt) reached JIS F*** level. However, bio-crude formulated BPF adhesives reduced the tension shear strength of bonded 3-ply plywood, in particular at higher formulation ratios. At the same bio-crude formulation ratio, WSP bio-crude formulated BPF adhesives gave better tension shear strength for 3-ply plywood than the WBB bio-crude formulated BPF adhesives. Nevertheless, 3-ply plywoods bonded with bark bio-crude formulated BPF adhesives at a ratio up to 50:50 (wt/wt) still met the JIS standards with respect to tension shear strength.

CURING CHARACTERISTICS OF POLYURETHANE MODIFIED UNSATURATED POLYESTER RESIN/COLOR PASTE MIXTURES

Viscosity and curing characteristics of polyurethane modified unsaturated polyester( PU-UPES) /color paste mixtures were systematically studied. The results showed that the viscosity of PU-UPES / color paste mixtures tends to increase with the content of the color paste,but the experimental data of viscosity are lower than the theoretical additive data. With the increasing of the color paste content,all of the gelation time,the apparent initial curing temperature and the apparent peak curing temperature increase accordingly,while the apparent final curing temperature and the enthalpy decrease. With the increasing of the heating rate,the curing characteristic temperatures of composite systems shift toward higher temperature values when the composite under the same content of color paste,but the curing enthalpy values are almost constant. Meanwhile,based on the the apparent peak curing temperature at different heating rates,the apparent activation energy and the preexponential factor of PU-UPES / color paste mixture curing reaction can be calculated through the Kissinger equation. The initial curing temperature,the peak curing temperature and the final curing temperature are calculated by the extrapolation method in order to optimize the curing process. Based on the optimum curing process,the adhesion grades of PU-UPES / color paste coatings are above the first level.

Curing-Induced Distortion Mechanism in Adhesive Bonding of Aluminum AA6061-T6 and Steels

The bonding of dissimilar materials is of primary importance to the automotive industry as it enables designers the freedom to choose from a wide variety of low density materials such as aluminum and magnesium. However, when two dissimilar materials (e.g., aluminum-to-steel) are bonded by curing at elevated temperatures, residual stresses result upon cooling the layered material system to room temperature. Problems such as distortion and fracture of adhesive often emerge in bonding of these dissimilar materials for automotive applications. In this study, the transient distortion of riveted and rivet-bonded aluminum AA6061-T6-to-steels during the curing process was investigated using the photographic method. The influences of temperature, adhesive properties, adherend thickness, adherend strength, and the presence of constraints on the transient distortion and adhesive fracture were evaluated. The peak curing temperature was found to play the most important role in distortion and adhesive fracture, followed by the influence of adherends thickness. In contrast, the other parameters studied such as the adhesive strength, constraints' type, and adherend strength produced a limited effect on distortion. The results provide useful information about vehicle body structure's design in reducing the curing induced distortion.

Effects of Hardeners on the Low-Temperature Snap Cure Behaviors of Epoxy Adhesives for Flip Chip Bonding

Various adhesive materials are used in flip chip packaging for electrical interconnection and structural reinforcement. In cases of COF(chip on film) packages, low temperature bonding adhesive is currently needed for the utilization of low thermal resistance substrate films, such as PEN(polyethylene naphthalate) and PET(polyethylene terephthalate). In this study, the effects of anhydride and dihydrazide hardeners on the low-temperature snap cure behavior of epoxy based non-conductive pastes(NCPs) were investigated to reduce flip chip bonding temperature. Dynamic DSC(differential scanning calorimetry) and isothermal DEA(dielectric analysis) results showed that the curing rate of MHHPA(hexahydro-4-methylphthalic anhydride) at <TEX>$160^{\circ}C$</TEX> was faster than that of ADH(adipic dihydrazide) when considering the onset and peak curing temperatures. In a die shear test performed after flip chip bonding, however, ADH-containing formulations indicated faster trends in reaching saturated bond strength values due to the post curing effect. More enhanced HAST(highly accelerated stress test) reliability could be achieved in an assembly having a higher initial bond strength and, thus, MHHPA is considered to be a more effective hardener than ADH for low temperature snap cure NCPs.

Preparation and properties of maleimide‐functionalized hyperbranched polysiloxane and its hybrids based on cyanate ester resin

AbstractA new hyperbranched polysiloxane containing maleimide (HPMA) was synthesized through the reaction between N‐(4‐hydroxyphenyl) maleimide and 3‐glycidoxypropyltrimethoxysilane, which was then used to prepare cyanate ester (CE) resin‐based hybrids (coded as HPMAx/CE, where x is the weight fraction of HPMA in the hybrid). The curing behavior of uncured hybrids and the typical properties (impact strength and dielectric properties) of cured hybrids were systemically investigated. Results show that the performance of hybrids is greatly related with the content of HPMA. Hybrids have obviously lower curing temperature than CE, overcoming the poor curing characteristics (higher curing temperature and longer curing time) of neat CE, for example, the curing peak temperature of HPMA20/CE is about 65°C lower than that of CE. In the case of cured resin and hybrids, the hybrids exhibit decreased dielectric constant and loss than CE resin; moreover, the former also exhibits lower water absorption than the latter. Specifically, the dielectric loss of HPMA15/CE hybrid is only about 27% of that of neat CE resin. In addition, the hybrids with suitable contents of HPMA have significantly improved impact strengths. The overall improved properties suggest that HPMAx/CE hybrids have great potential in applications needing harsh requirements of curing feature, dielectric properties, and toughness. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and characterizations of a latent polyhedral oligomeric silsequioxane‐containing catalyst and its application in polybenzoxazine resin

AbstractIn this article, a novel latent curing agent, octa(paratoluenesulfonic acid ammomium salt) (OPAAS) polyhedral oligomeric silsequioxane was synthesized and used in modifying the polybenzoxazine/2,2′‐(1,3‐phenylene)‐bis(4,5‐dihydro‐oxazoles) (PBO) (PBZ/PBO) resin. The liberated octa(aminophenyl) silsesquioxane and paratoluenesulfonic acid can catalyze the ring‐opening reaction of benzoxazine (BZ) resin. The initial curing temperature (Ti), peak curing temperature (Tp) and the Enthalpy of the curing temperature had significantly decreased with respect to pristine BZ/PBO resin. When the OPAAS amount was 3 wt %, the peak curing temperature decreased from 233.7 to 218.2°C. Also, PBZ/PBO/OPAAS composites exhibited better storage modulus than pure PBZ/PBO resin. Meanwhile, PBZ/PBO/OPAAS composites are more thermally stable than PBZ/PBO resin. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Effect of functionalized multi-walled carbon nanotubes on the curing behavior and thermal stability of epoxy resin

Multi-walled carbon nanotubes (MWNTs) were modified by triethlene-tetramine (TETA) in order to attain better dispersibility and stronger interfacial bonding between MWNTs and epoxy matrix. The influence of surface treated MWNTs on the cure behavior of the diglycidyl ether of bisphenol A (DGEBA)/2-ethyl-4-methyl imidazole (EMI-2,4) system was investigated with nonisothermal differential scanning calorimetry. It was found that the curing peak temperature ( TP) decreased with the addition of TETA-MWNTs. The curing apparent activation energy ( Ea) was calculated through Kissinger method. In addition, the thermal behavior of TETA-MWNTs/DGEBA/EMI-2,4 was examined by thermogravimetric analysis, and the result showed the addition of TETA-MWNTs could increase the thermal decomposition onset temperature ( TB) and the degradation peak temperature ( Tmax) of the nanocomposites. Scanning electron microscopy images of fractured surface of MWNTs/epoxy indicated homogeneous dispersibility of TETA-MWNTs and strong interfacial adhesion between the TETA-MWNTs and the epoxy matrix in the nanocomposites.

Curing, Thermal and Mechanical Properties of Liquid Crystalline p-SBPEPB/BPAER/DDE System

The curing, thermal and mechanical properties of bi-component system for bisphenol A epoxy resin (BPAER) modified by liquid crystalline Sulfonyl bis(4,1-phenylene)bis[4-(2,3-epoxypro pyloxy)benzoate] (p-SBPEPB), with 4,4'-diaminodiphenyl ether (DDE) as a curing agent, were investigated. The effect of the different liquid crystalline contents and the heating rate on curing reaction was discussed. The results show that the curing peak temperature decreases, curing rate increases, the glass transition temperature (Tg)and impact strength all increase with adding of liquid crystalline p-SBPEPB when the content is not over 8wt%.

A Novel Formaldehyde-Free Adhesive from Jatropha Curcas Press-cake

Jatropha curcas (Jc) was the most favored biomass plant for bio-diesel production. Jc cakes obtained after oil pressed, rich in protein content, were excellent materials for preparing formaldehyde-free wood adhesives, which could provide alternative to formaldehyde-based resins. Sodium hydroxide, used as denaturing agent, modified protein contained in Jc cakes to prepare wood adhesives. Jc adhesives prepared in different pH value and plywood bonded by them were prepared. The curing behavior of these adhesives was conducted by differential scanning calorimetry (DSC) measurement. The gel content and water absorption of the cured Jc adhesives were measured to evaluate their curing content and the water resistant of plywood bonded with these adhesives was also studied. The results showed that pH value influenced the bonding strength of adhesive significantly. The bonding strength of plywood made by modified Jc adhesive significantly increased comparing with that of unmodified one. The curing peak temperature decreased obviously after modified, which was beneficial to achieve complete curing reaction. Modified Jc adhesives provided a potential way to utilize by-product of energy plant, avoided formaldehyde pollution, and reduced dependence on fossil resources.

Preparation and Characterisation of Polyaniline Grafted Multiwalled Carbon Nanotubes/Epoxy Composite

Dodecyl benzene sulfonic acid (DBSA) doped polyaniline (PANI) grafted MWNTs (PANI-g-MWNTs)/Epoxy composite were prepared by aniline in situ polymerization in the presence of phenylamine groups contained MWNTs followed by solution blending and mould casting. Phenylamine groups grafted on the surface of MWNTs via amide bond join in the in situ polymerization and MWNTs are encapsulated by PANI coatings forming a core (MWNTs)-shell (PANI) nano-structure. DBSA doped PANI coatings swell in tetrahydrofuran (THF) and core-shell nano-structures are stabilized in epoxy solution, which is in favor of MWNTs dispersion in epoxy resin and formation of a homogenous MWNTs/Epoxy composite. After DBSA doped PANI-g-MWNTs are introduced in Epoxy, initial curing and exothermic peak temperatures as well as curing reaction enthalpy decrease, which indicates addition of DBSA doped PANI-g-MWNTs promotes curing reaction of Epoxy. Tensile strength, Young’s modulus, elongation at break, flexural strength and flexural modulus of the composite are improved by 71.7%, 42.3%, 99.8%, 55.01% and 39.86% compared with Epoxy, respectively.

CHITOSAN IN APPLICATIONS OF BIOMEDICAL DEVICES

Chitosan is a natural polysaccharide with great potential for biomedical applications due to its biocompatibility, biodegradable capability, and nontoxicity. Various techniques used for preparing chitosan microspheres/membranes and evaluations of these fabrications have also been reviewed. The hydrophilicity of chitosan provides unique characteristics of hydrogel formation with the acidic media and may entrap the drug content inside of the matrix for controlled release. In order to improve upon the scope of preparation of chitosan microspheres, we had successfully employed and incorporated a high-voltage system into the direct pumping injection process. The wide range of drug release profiles could be attributed to the surface characteristics, porosities, and various structures of chitosan microspheres upon treatment with Na5P3O10/NaOH solutions of various volume ratios. We also demonstrated that with the addition of chitosan/β-TCP microspheres as a constituent into the PMMA cement significantly decreases the curing peak temperature and increases the setting time. The excellent gelforming property of chitosan offers another biomedical application in membrane separation fields. Chitosan membranes were prepared by a thermal induced phase separation method, following treatment with nontoxic NaOH gelating and Na5P3O10, Na2SO3 crosslinking agents. In order to further improve the mechanical strength and biocompatibility and to expand the potential of chitosan GTR membranes in periodontal applications, various chitosan membranes incorporating with negatively charged alginate, bioactive tricalcium phosphate, and platelet rich plasma, respectively, were also prepared and characterized. Moreover, we had also utilized chitosan, which with good blood-clotting, cheap, and easy preparation characteristics, as the raw material to prepare rapid clotting wound dressing and tooth plug.