Curing Characteristics Research Articles

Thermal degradation and curing kinetic study of urea formaldehyde/l-tyrosine composites

In this study, the prepolymers (TYF) were prepared by formaldehyde and l-tyrosine, different amounts of TYF were added to prepare TYF modified urea-formaldehyde adhesives (LUF), and the gel time of resin, formaldehyde emission and wet shear strength of the plywood were tested. This result indicated that the optimal addition amount was 3 wt%, and the formaldehyde emission of plywood decreased by 23% to 0.57 mg/L, and the wet shear strength increased by 47% to 1.47 MPa. The thermal degradation and curing characteristics of urea-formaldehyde (UF) and LUF resins were characterized by thermogravimetric (TG) and differential scanning calorimetry (DSC), and the kinetic parameters were analyzed. The results showed that TYF could reduce the formaldehyde emission and improve the wet shear strength significantly. Moreover, the thermal degradation activation energy (Eα) of UF resin was increased, and the thermal stability was enhanced. Although the initial and peak curing temperatures of LUF were higher, but the LUF cured more easily than the UF once the curing temperature was reached.

Effect of Polynorbornene on Physico-Mechanical, Dynamic, and Dielectric Properties of Vulcanizates Based on Isoprene, α-Methylstyrene-Butadiene, and Nitrile-Butadiene Rubbers for Rail Fasteners Pads

The article studies the effect of polynorbornene (PNB) in the composition of PNB with Norman 747 LV plasticizer (RC) on the curing characteristics of the rubber compound and the physico-mechanical, dynamic, dielectric properties and the thermal behavior of vulcanizates based on a combination of isoprene, α-methylstyrene-butadiene, and nitrile-butadiene rubbers. It is shown that vulcanizates containing PNB in the composition of the RC had lower conditional tensile strength, hardness, and tear resistance compared to the vulcanizate of the base version of the rubber compound. Studies of dynamic mechanical analysis indicate that an increase in the content of RC, and hence PNB, in the rubber compound contributes to an increase in the mechanical loss factor (tanδ) and a decrease in the storage modulus of vulcanizates. It was found that vulcanized rubber, containing 24.0 parts per hundred of rubber (phr) (8.98 wt. %) PNB as part of the RC, is characterized by stable physico-mechanical, improved vibration-absorbing properties, as well as increased dielectric parameters. This rubber compound can be used as a base for rail fasteners for railroad tracks.

Laboratory evaluation of environmentally friendly alternative mineral powders for micro-surfacing treatments manufacture

The effectiveness of using alternative environmentally friendly and cost-effective mineral powders to manufacture micro-surfacing treatments is examined. Four mineral powders (calcium carbonate, dolomite, PAVAL, and mineral dust from the recycling of used toner) as well as Portland cement (control) were used. The use of two of them, the PAVAL and the toner, is the main novelty of the present research. Their granulometry by means of an air jet sieve, their density, and their chemical composition by means of X-ray fluorescence (XRF) were obtained. To generalise the findings, two different types of aggregate (siliceous and porphyritic) have been used to manufacture the micro-surfacing treatment. The mixing time, setting and curing characteristics, and workability were analyzed. Additionally, the resistance to the loss of particles by the wet track abrasion was also studied. Likewise, the consistency assessment was done. Finally, the cohesion also was attained. The micro-surfacing treatments manufactured with all the alternative mineral powders comply with the technical requirements. Moreover, they improve the loss of particles, particularly the toner, with a loss of particles between 87% and 280% lower than the control micro-surfacing. Also, they are less hardening-controlling additive demanding. Particularly the PAVAL needs 0.2% of additive while the control micro-surfacing needs 0.6%. These findings are supported by statistical analysis of variance (ANOVA).

Recycled silica as a renewable and sustainable alternative to carbon black in natural rubber foams

AbstractSustainable natural rubber foams were prepared by replacing petroleum‐based carbon black (CB) with recycled silica (SiO2) nanoparticles. The total nanofiller concentration was fixed at 40 phr, while the CB/silica ratio was changed from 40/0 to 0/40. The results showed that increasing the silica content increased the curing characteristics, such as delta torque (ΔM) by 54%, scorch time (ts) by 50% and optimum curing time (t90) by 65%. But foams based on a hybrid system (20/20) produced a more homogeneous structure improving the cell nucleation step and leading to the smallest cell size (18 μm) and highest cell density (8.8 × 103 cells mm−3) due to reduced filler−filler interactions and better particle dispersion. This improved cellular morphology generated superior mechanical and thermal insulation performance, including the highest compression modulus (2.7 MPa), compressive strength (1.9 MPa) and recoverability (96.6%) combined with the lowest thermal conductivity (0.114 W m−1 K−1) at a density of 0.652 g cm−3. Nevertheless, the foam with 40 phr silica showed higher compressive modulus (26%) and compression strength (15%) compared to the reference sample having 40 phr CB, mainly due to its higher crosslink density. As a final comparison, the recycled silica, being a suitable and sustainable alternative to petroleum‐based CB, showed superior mechanical and thermal insulation properties compared to a commercial grade of silica for natural rubber foams. © 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry.

Effect of Process Parameters on Thermal and Mechanical Properties of Filament Wound Polymer-Based Composite Pipes.

The aim of this study was to investigate the mechanical and thermal properties of composite pipes based on epoxy resin and glass fibers produced by filament winding (FW) technology. Epoxy resins are widely used polymers in FW composite structures. The thermal characterization of the neat epoxy resin, curing, and post-curing characteristics for the determination of polymerization and glass transition temperature was performed, which is important for the mechanical properties of polymer composite pipes. In the present work, the applicability of the full factorial experimental design in predicting the hoop tensile and compressive strengths of glass fiber/epoxy resin composite pipes was investigated. The composite pipes in accordance with the 23 full factorial experimental design by using of three parameters and two levels of variation were prepared. The winding speed of the composites was taken to be the first factor, the second was the fiber tension, and the third was winding angle. To approximate the response, i.e., the mechanical properties of the composite pipes within the study domain, the first-order linear model with the interaction was used. The influence of each individual factor to the response function was established, as well as the influence of the interaction of the two and three factors. Additionally, those results were completed with the thermal characterization of the polymer composite pipes. From received results from mechanical and thermal characterization, it was concluded that the properties of composite specimens were highly affected by the analyzed parameters in filament winding technology. It was found that the estimated first-degree regression equation with the interaction gave a very good approximation of the experimental results of the hoop tensile and the compressive strengths of composite pipes within the study domain.

Modeling of the effect of ATH fillers on the rheology, curing kinetics, and flexural properties of the epoxy resin forming the hydraulic turbines’ stay vanes extension

Epoxy resins are crucial for the production of GFRP/XPS foam sandwich structures used for hydraulic turbine extension stay vanes. The quantity and size of ATH fillers have a significant impact on the curing and post-curing characteristics of the epoxy resin. This paper presents the results of an experimental study of the effect of ATH fillers on the maximum temperature, polymerization time, shrinkage, viscosity, and flexural properties of the epoxy resin. The study also uses regression and neural network methods to develop models to predict these properties based on ATH mass fraction and particle size. The results showed that increasing the mass fraction of ATH with a smaller particle size delayed polymerization and reduced the maximum temperature. The addition of ATH resulted in an improvement of the flexural modulus; nevertheless, it caused a reduction in both the flexural strength and breakage strain. Adding ATH improved flexural strength, modulus, and breakage strain. The models developed in this study had a high correlation between predicted and measured responses, providing valuable information for the design and casting of the proposed sandwich structures.

Effect of carbon nanotubes on curing characteristics of low energy electron beam curing CFRPs

AbstractLow energy electron beam (E‐Beam) curing process has been considered a promising fabrication technology in high‐efficiency and low‐cost OOA curing, but still not been widely used in industrial applications, mainly limited by the poor mechanical properties of the CFRP resulting from the poor toughness of the low‐energy E‐Beam curable resin. This paper extended the excellent effect of carbon nanotubes (CNTs) toughened resin to the E‐Beam curable resin system, and focused on the influence law and mechanism of CNTs on the curing characteristics of the resin. Theoretical analysis showed that the carboxylated CNTs affect the curing characteristics by participating in the chain transfer link of the cationic curing process. According to the DSC experimental results, the activation energy of the curing reaction of the resin were reduced from 136.2 kJ·mol−1 without adding CNTs to 123.9 kJ·mol−1, 118.3 kJ·mol−1, 112.8 kJ·mol−1 and 105.8 kJ·mol−1 at 0.25 wt.%, 0.5 wt.%, 0.75 wt.% and 1 wt.% of CNTs adding amount respectively, due to which the curing degree of the E‐Beam curable CFRPs were improved with the increase of CNTs contents. Considering the E‐Beam dose attenuation and its influence on curing characteristics, prepregs were irradiated single‐sided or both sided for efficient preparation of E‐Beam cured CFRP components subsequently, for which the curing degree along the prepreg thickness were investigated through the curing reaction kinetic models and DSC experiments. This study will provide research basis for parameter optimization of CNTs contents, and performance improvement of E‐Beam cured CNTs/CFRP.

3D printing of high-precision and ferromagnetic functional devices

The development of projection-based stereolithography additive manufacturing techniques and magnetic photosensitive resins has provided a powerful approach to fabricate miniaturized magnetic functional devices with complex three-dimensional spatial structures. However, the present magnetic photosensitive resins face great challenges in the trade-off between high ferromagnetism and excellent printing quality. To address these challenges, we develop a novel NdFeB-Fe3O4 magnetic photosensitive resin comprising 20 wt.% solid loading of magnetic particles, which can be used to fabricate high-precision and ferromagnetic functional devices via micro-continuous liquid interface production process. This resin combining ferromagnetic NdFeB microparticles and strongly absorbing Fe3O4 nanoparticles is able to provide ferromagnetic capabilities and excellent printing quality simultaneously compared to both existing soft and hard magnetic photosensitive resins. The established penetration depth model reveals the effect of particle size, solid loading, and absorbance on the curing characteristics of magnetic photosensitive resin. A high-precision forming and ferromagnetic capability of the NdFeB-Fe3O4 magnetic photosensitive resin are comprehensively demonstrated. It is found that the photosensitive resin (NdFeB:Fe3O4 = 1:1) can print samples with sub-40 μm fine features, reduced by 87% compared to existing hard magnetic photosensitive resin, and exhibits significantly enhanced coercivity and remanence in comparison with existing soft magnetic photosensitive resins, showing by an increase of 24 times and 6 times, respectively. The reported NdFeB-Fe3O4 magnetic photosensitive resin is anticipated to provide a new functional material for the design and manufacture of next-generation micro-robotics, electromagnetic sensor, and magneto-thermal devices.

Potential Utilization of Ground Eggshells as a Biofiller for Natural Rubber Biocomposites.

The aim of this work was application of ground eggshells in various amounts by weight as a biofiller for natural rubber (NR) biocomposites. Cetyltrimethylammonium bromide (CTAB), ionic liquids (ILs), i.e., 1-butyl-3-methylimidazolium chloride (BmiCl) and 1-decyl-3-methylimidazolium bromide (DmiBr), and silanes, i.e., (3-aminopropyl)-triethoxysilane (APTES) and bis [3-(triethoxysilyl)propyl] tetrasulfide (TESPTS), were used to increase the activity of ground eggshells in the elastomer matrix and to ameliorate the cure characteristics and properties of NR biocomposites. The influence of ground eggshells, CTAB, ILs, and silanes on the crosslink density, mechanical properties, and thermal stability of NR vulcanizates and their resistance to prolonged thermo-oxidation were explored. The amount of eggshells affected the curing characteristics and crosslink density of the rubber composites and therefore their tensile properties. Vulcanizates filled with eggshells demonstrated higher crosslink density than the unfilled sample by approximately 30%, whereas CTAB and ILs increased the crosslink density by 40-60% compared to the benchmark. Owing to the enhanced crosslink density and uniform dispersion of ground eggshells, vulcanizates containing CTAB and ILs exhibited tensile strength improved by approximately 20% compared to those without these additives. Moreover, the hardness of these vulcanizates was increased by 35-42%. Application of both the biofiller and the tested additives did not significantly affect the thermal stability of cured NR compared to the unfilled benchmark. Most importantly, the eggshell-filled vulcanizates showed improved resistance to thermo-oxidative aging compared to the unfilled NR.

Application of mixture design of experiments to the development of alkali-activated composites based on chamotte and waste glass

Alkali-activated binders have been indicated as possible replacement for Portland Cement with environmental benefits. However, an adequate dosage of raw materials and alkalis content is mandatory to obtain alkali-activated materials with suitable physical and mechanical characteristics. The aim of this work is the application of mixture design of experiments to determine optimal dosages for pressed alkali-activated composites based on two precursors: chamotte (C) and waste glass (WG). Fine sand (S) was used as aggregate. Ten mixtures were obtained from the experimental design, and cylindrical samples were cast by uniaxial pressing. The alkalis/precursor ratio was kept constant for all the mixtures. After curing, the physical, mechanical and microstructural characteristics of the specimens were assessed. The application of desirability function revealed that the optimal composition was the one with higher content of sand (50%), 30% chamotte and 20% waste glass. The addition of sand contributed to reduce porosity and increase the particle packing, promoting the increase of mechanical strength. Regarding compressive strength, almost all the mixtures met the requirement for solid bricks. This study demonstrates the potential of using mixture design of experiments as an efficient tool to determine the proper composition and predict the behavior of waste-based alkali-activated materials.

Evaluation of the effects of asphalt binder aging degree on the curing, compatibility, and mechanical behaviors of epoxy asphalt binders

The application of epoxy asphalt binder in hot mix plant recycling for reclaimed asphalt pavement (RAP) can significantly increase the utilization rate of waste material on the premise of ensuring the service quality of the asphalt pavement. However, the development of epoxy asphalt binder modified RAP is hindered by the limited understanding of the effect of aging degree and types variability of asphalt binder in RAP on the properties of epoxy asphalt binder. Therefore, short-, long- and ultra-long- term aging tests of base asphalt and SBS modified asphalt binder were conducted through rolling thin film oven (RTFO), pressure aging vessel (20 h and 40 h) tests to obtain the asphalt binders with different aging extent, and then the binders were mixed with two epoxy systems to prepare epoxy asphalt binders, respectively. Next, the effects of asphalt binders aging degree on curing, compatibility, and mechanical behaviors characteristics of epoxy asphalt binders were investigated from chemical, microscopic, mechanical, and rheological perspectives based on Brookfield viscosity, Fourier transform infrared (FTIR), laser confocal fluorescence microscopy (LSCM), Shore hardness, direct tensile, strain sweep, and frequency sweep tests. The viscosity results indicated that a higher asphalt binder aging degree brought about a faster increase in the viscosity of epoxy asphalt binders. The construction allowable time of type-A epoxy asphalt binder of at least 3.5 h was higher than that of type-B. The conversion degree model constructed with the 917 cm−1 peak area as a parameter showed that the epoxy asphalt binder prepared by the asphalt binder with a more severe aging degree presented a higher conversion degree within the same curing time since the reaction space between epoxy and curing agent reactive groups was compressed by aggregated aged asphalt binder. The LSCM and Shore hardness results suggested that the aging asphalt binders induced the phase separation between asphalt and epoxy resin. With the asphalt binders aging, the distribution of asphalt phase in the epoxy system changed from black dots (12–15 um) to island-shaped structures (50–98 um), and eventually transferred a neuron-shaped network structure to connect island-shaped synaptosomes to block the continuity of three-dimensional network structure of epoxy resin. The rheological tests showed that the linear viscoelastic (LEV) region of the epoxy asphalt binders changed with the asphalt binders aging degree, and a shear strain of 0.01% ensured that specimens was within the LEV region. The effects of asphalt binders aging degree on the complex modulus and phase angle master curves of type-A epoxy asphalt binders mainly reflected the low frequency region (10−4 to 10−1 Hz), while the effects on type-B epoxy asphalt binders were in the whole frequency range (10−4 to 103 Hz).

Effects of powder properties on the 3D printing of BaTiO3 ceramic resins by stereolithography

Stereolithography is a layer-by-layer building fabrication technique enabling production of advanced ceramic 3D shapes that are not achievable by other methods. Critical parameters of stereolithography are associated with the preparation of a ceramic resin exhibiting suitable rheological and optical properties, as well as tunable curing property to achieve the desired level of resolution of complex 3D parts. However, tailoring the cure depth for each layer is challenging for functional ceramics due to their high refractive index giving increased light scattering. Here, the stereolithography 3D printing of BaTiO3 ceramic resins is investigated by employing a desktop 3D printer (λ = 405 nm) and a commercial base resin. The effects of two BaTiO3 powders with different size distributions (one micro-sized powder with grains in the range 1–20 µm, and one agglomerated nano-sized powder in the range 60–100 nm), on the viscosity and curing characteristics of the ceramic resins were investigated. It is shown that the nano-sized powder resulted in increased viscosity, increased scattering, and reduced cure depth compared to the micro-sized BaTiO3 ceramic resin. In general, the cure depth decreased with increasing ceramic loading. Successful prints were obtained for an overcuring of at least 40% between layers to assure good adherence between the layers. The printing properties of the ceramic resins from both powders were suitable for printing green parts with 50 µm layer thickness.

Preparation of semi-interpenetrating networks of phthalonitrile and polyetherimide resin: study of their curing characteristics and thermal properties

Preparation of semi-interpenetrating networks of phthalonitrile and polyetherimide resin: study of their curing characteristics and thermal properties

Synergistic behavior of dual filler system (n‐Si3N4/COOH‐MWCNT) on the mechanical, tribological, curing, and corrosion characteristics of epoxy hybrid nanocomposites

AbstractEpoxy hybrid nanocomposites reinforced with silicon nitride nanoparticles (SiN) and carboxylic acid‐modified multiwalled carbon nanotubes (COOH‐MWCNT) were prepared by hand layup. These hybrid nanocomposites have not undergone thorough investigation in the fields of mechanical, tribological, and corrosion‐resistant characteristics. The 0.25/0.5 SiN/MWCNT hybrid nanocomposite displayed improvement in elongation by 190% and fracture toughness by 360%. The effect of dual filler system on the wear and friction properties of the composite was investigated. The influence of silicon nitride and hybrid fillers the curing characteristics of epoxy was examined using Fourier transform infrared spectroscopy (FTIR). From differential scanning calorimetry (DSC), it was found that the use of dual fillers in the epoxy system reduced the residual heat of reaction and curing time by 15%. In a highly corrosive environment (3.5% NaCl), TAFEL polarization showed that 0.5/0.5 SiN/MWCNT epoxy hybrid coating on mild steel (MS) increased protection against corrosion by 30%. The dispersion of nanofillers and their interactions were verified using high‐resolution transmission electron microscopy (HR‐TEM). The morphology of the fracture, wear, and corroded surfaces were examined by field emission scanning electron microscopy (FE‐SEM). SiN manifested a synergistic effect with MWCNTs making it a superior reinforcement at very low content.

The preparation of anisotropic conductive paste and its application in FOB interconnection

PurposeThe purpose of this study is to investigate the reliability of flex-on-board (FOB) interconnection connected with an anisotropic conductive paste (ACP), which is prepared by dispersing nickel balls in the epoxy-curing system.Design/methodology/approachDifferential scanning calorimetry was used to evaluate the curing characteristics of the paste. And the contact resistances of bonding joints and 90º peel adhesion were tested before and after high temperature and high humidity test (85°C, 85% humidity), thermal cycling (−45°C∼125°C, 30min/cycle) and pressure cooker test (PCT, 121°C, 100% humidity 2 atm) to evaluate the flex on board (FOB) interconnection reliability.FindingsIt is found that FOB test vehicles have been successfully bonded by using ACP for the first time. And the ACP bonding joint of FOB has good reliability and can meet the requirements of FOB interconnection. Compared with conventional anisotropic conductive film (ACF), this ACP interconnection provides higher adhesion strength, higher joint current carrying capability and higher reliability performance and lower cost for FOB interconnection.Originality/valueACP is applied in the interconnection of FOB. It has the higher reliability performance and lower cost for than the conventional ACF.

Automatic dispersion, defect, curing, and thermal characteristics determination of polymer composites using micro-scale infrared thermography and machine learning algorithm

Infrared thermography is a non-destructive technique that can be exploited in many fields including polymer composite investigation. Based on emissivity and thermal diffusivity variation; components, defects, and curing state of the composite can be identified. However, manual processing of thermal images that may contain significant artifacts, is prone to erroneous component and property determination. In this study, thermal images of different graphite/graphene-based polymer composites fabricated by hand, planetary, and batch mixing techniques were analyzed through an automatic machine learning model. Filler size, shape, and location can be identified in polymer composites and thus, the dispersion of different samples was quantified with a resolution of ~ 20 µm despite having artifacts in the thermal image. Thermal diffusivity comparison of three mixing techniques was performed for 40% graphite in the elastomer. Batch mixing demonstrated superior dispersion than planetary and hand mixing as the dispersion index (DI) for batch mixing was 0.07 while planetary and hand mixing showed 0.0865 and 0.163 respectively. Curing was investigated for a polymer with different fillers (PDMS took 500 s while PDMS-Graphene and PDMS Graphite Powder took 800 s to cure), and a thermal characteristic curve was generated to compare the composite quality. Therefore, the above-mentioned methods with machine learning algorithms can be a great tool to analyze composite both quantitatively and qualitatively.

Studies on thermoset blend of bismaleimide having multiple swivel groups and biscyanate ester

The materials 2,2-bis [4-(4-maleimidophenoxy phenyl)] propane (BMIX) and bisphenol-A based cyanate ester (BCY) were synthesized. The monomers BMIX and BCY were physically blended (BMCY) in 1:1 mol ratio. The materials BMIX, BCY and BMCY were thermally polymerized and the structural characterisation of the materials was done using Fourier transform infrared spectrophotometer (FTIR). The curing characteristics of BMIX, BCY and its blend (BMCY) were investigated using differential scanning calorimeter (DSC). The blend BMCY shows considerable differences in the thermal curing behaviour as evidenced by the DSC studies. Blending BCY with BMIX drastically reduces the melting temperature, curing onset temperature and the amount of heat liberated during thermal curing. The thermal stabilities of the crosslinked network polymers (PBMIX, PBCY and PBMCY) were investigated using thermogravimetric analyser (TGA). Detailed TGA studies indicated that the PBMCY shows better thermal stability than the PBMIX and PBCY. The DSC and TG curves indirectly hint about the possible reaction between BMIX and BCY during thermal curing. Woven glass fibre reinforced laminates were prepared using BMIX, BCY and BMCY by solution impregnation followed by drying and compression moulding. The glass laminate having BMCY as the matrix resin showed much better mechanical property (tensile strength) compared to the laminate made using BMIX as the matrix resin.

Sustainable plasticizer from agroindustrial waste for natural rubber compounds: Influence on the curing system and compound properties

The industry has pursued efforts to minimize the use of fossil fuel-based processing oils in favor of naturally occurring nontoxic oils from renewable sources, such as vegetable oils. In this study, the feasibility of replacing naphthenic oil (NAPH)-based plasticizers in natural rubber (NR) compounds with oil originating from cashew nut shells was evaluated. Cardanol oil (Cdn), which is derived from decarboxylated cashew nut shell liquid, a byproduct of cashew nut production, was chemically modified by acetylation and named Cdn-A. The successful acetylation of Cdn with acetic anhydride was confirmed. The effects of Cdn and Cdn-A as plasticizers on the curing characteristics, thermal aging, and physical, mechanical, and dynamic properties of carbon black-filled NR compounds were then evaluated. Cdn acted as a co-activator for rubber vulcanization; by contrast, Cdn-A showed negligible effects on this process. Vulcanized Cdn- and Cdn-A-containing NR compounds exhibited improved abrasion and tear resistance compared with the reference compound containing NAPH, as well as antioxidant activity. The Cdn-added NR compound also demonstrated high elongation at break and toughness. The results collectively suggest that NR compounds containing Cdn exhibit properties suitable for tire tread applications requiring high grip characteristics.

Evaluation of suitability of sesame oil as an alternative for aromatic processing oil in natural rubber composites

Polycyclic aromatic oils, high in aromatic content are used in tyre compounds as processing aids and these have been found to be carcinogenic. Therefore, it is necessary to find processing aids consisting of a low content of aromatics which would help to overcome the problem associated with the use of petroleum-based aromatic oils. The main aim of this research was to develop carbon black filled natural rubber (NR) composites using environmentally friendly sesame oil as the processing aid. Initially sesame oil was characterized using Fourier Transform Infra-Red analysis. Thereafter, a series of NR based tyre tread compounds was prepared by varying the sesame oil loading from 3-9 phr at 2 phr intervals. Cure characteristics, physico-mechanical and swelling properties of these composites were evaluated and compared with those of the composite prepared with the aromatic processing oil, Dutrex-R (control). Dispersibility of carbon black in all the NR composites was assessed. Viscosity, processing safety and cure rate of the composite produced with 5 phr sesame oil were higher compared to the control and indicated that the oil behaves as a co-activator in rubber compounds. Hardness, modulus at 100% elongation and abrasion volume loss of the vulcanizates prepared with more than 5 phr sesame oil were lower, whereas tensile strength, elongation at break and resilience were higher than those of the control. Tear strength and compression set of the vulcanizates prepared with 5 phr sesame oil were comparable to those of the control. Further, the former vulcanizate showed a higher and lower swelling indices in toluene and water, respectively compared to the control. Furthermore, the vulcanizates prepared with sesame oil showed better ageing resistance in comparison to the control. Hence, sesame oil could be a suitable alternative for Dutrex-R in tyre tread compounds at 5 phr level.

Technological properties of a branched polyethyleneimine derivative as a cross-linker for low molar ratio urea-formaldehyde resins

To address formaldehyde release problem, low-molar-ratio UF resin has become the industry's major adhesive for bonding wood-based panels. Unfortunately, its drawbacks of poor water resistance, low bonding strength and slow curing rate lead to low production efficiency and inferior dimensional stability of wood-based products. In this work, a branched polymer-based functional agent (BPG) as a crosslinker was synthesized from branched polyethyleneimine (BPEI), urea and glyoxal via two steps with deamination and Mannich reaction for promoting the performance of low-molar-ratio UF resin in wood bonding. The FTIR confirmed the successful synthesis of the long-branched BPG-bearing active aldehyde group (-CHO) as expected. The effects of BPG on curing characteristics, bonding strength and water resistance of UF resin were evaluated using DSC and tensile shearing strength measurement, respectively. Results showed that UF resin cured by BPG displayed a lower curing temperature, faster curing rate and exhibited superior wet bonding strength, 1.37 MPa, nearly two times higher than that cured by a traditional curing agent (NH4Cl). In addition, TG, XRD, FT-IR and SEM analysis confirmed that UF/BPG mixture showed excellent thermostability, compact and continuous microstructure, and decreased crystal structure due to the dense network structures in cured UF/BPG resin. These results demonstrated that BPG was an efficient crosslinker for improving the bonding strength and water resistance of low-molar-ratio UF polymer.