This study evaluates effects of aging on repair bond strengths of microhybrid, nanohybrid, and nanofilled composite resins and characterizes the interacting surfaces after aging. Disk-shaped ...composite specimens were assigned to one of three aging conditions: (1) thermocycling (5,000×, 5–55°C), (2) storage in water at 37°C for 6 months, or (3) immersion in citric acid at 37°C, pH 3 for 1 week; a non-aged group acted as the control. Two surface conditionings were selected: intermediate adhesive resin application (IAR-application) and chairside silica coating followed by silanization and its specific IAR-application (SC-application). Composite resins, of the same kind as their substrate, were adhered onto the substrates, and repair shear bond strengths were determined, followed by failure type evaluation. Filler particle exposure was determined by X-ray photoelectron spectroscopy and surface roughness analyzed using scanning electron and atomic force microscopy. Surface roughness increased in all composite resins after aging, but filler particle exposure at the surface only increased after thermocycling and citric acid immersion. Composite resin type, surface conditioning, and aging method significantly influenced the repair bond strengths (
p
< 0.05, three-way analysis of variance) with the least severe effects of water storage. Repair bond strengths in aged composite resins after IAR-application were always lower in non-aged ones, while SC-application led to higher bond strengths than IAR-application after thermocycling and water storage. In addition, SC-application led to more cohesive failures than after IAR-application, regardless the aging method.
Epoxy resin will continue to be in the forefront of many thermoset applications due to its versatile properties. However, with advancement in manufacturing, changing societal outlook for the chemical ...industries and emerging technologies that disrupt conventional approaches to thermoset fabrication, there is a need for a multifunctional epoxy resin that is able to adapt to newer and robust requirements. Epoxy resins that behave both like a thermoplastic and a thermoset resin with better properties are now the norm in research and development. In this paper, we viewed multifunctionality in epoxy resins in terms of other desirable properties such as its toughness and flexibility, rapid curing potential, self-healing ability, reprocessability and recyclability, high temperature stability and conductivity, which other authors failed to recognize. These aspects, when considered in the synthesis and formulation of epoxy resins will be a radical advance for thermosetting polymers, with a lot of applications. Therefore, we present an overview of the recent finding as to pave the way for varied approaches towards multifunctional epoxy resins.
A novel DOPO-containing imidazole curing agent (DIB) was successfully synthesized, and served as a co-curing agent of 4,4‘-diaminediphenyl sulfone (DDS) to prepare a reactive flame-retarded epoxy ...thermoset (EP/DDS/DIB). The DSC results showed that the curing temperature of EP/DDS/DIB mixture was much lower than that of EP/DDS mixture due to the catalytic curing effect of imidazole group. Although the Tg values of EP/DDS/DIB thermosets decreased in some degree, they were still obviously higher than that of EP/DDS/DOPO thermoset. The combustion tests indicated that DIB was a high-efficiency flame retardant for epoxy resin. The LOI value and UL94 rating of EP/DDS/DIB-0.75 sample reached 36.8% and V-0, respectively. In addition, the pk-HRR, av-HRR and THR of EP/DDS/DIB-1.0 thermoset were decreased by 57.2%, 37.9% and 36.0%, respectively, compared with those of EP/DDS thermoset. The studies concerning decomposition products in both condensed and gaseous phases revealed that the introduction of DIB brought about the formation of a protective intumescent char layer and the release of phosphorus-containing radicals and noncombustible nitrogen-containing fragments during combustion. DIB exerted bi-phase flame retardant effect on epoxy resin.
•A novel flame retardant imidazole curing agent (DIB) containing phosphaphenanthrene group was successfully synthesized.•The imidazole group in DIB catalyzed the curing reaction of DGEBA.•DIB endowed EP thermoset with excellent flame retardancy due to its bi-phased flame-retardant effect.
Increasingly strict regulations, as well as an increased public awareness, are forcing industry, including the foundry industry, to develop new binders for molding sands, which, while being more ...environmentally friendly, would simultaneously ensure a high quality of castings. Until recently, binders based on synthetic resins were considered to be such binders. However, more accurate investigations indicated that such molding sands subjected to high temperatures of liquid metal generated several harmful, even dangerous substances (carcinogenic and/or mutagenic) from the benzene, toluene, ethylbenzene and xylenes (BTEX) and polycyclic aromatic hydrocarbons groups (PAHs). An assessment of the most widely used molding sands technologies at present with organic binders (synthetic resins) from the no-bake group (furan no-bake and phenolic-ester no-bake) and their harmfulness to the environment and work conditions is presented in this paper. In the first stage of this research, gases (from the BTEX and PAHs groups) emitted when the tested molds were poured with liquid cast iron at 1350 °C were measured (according to the authors’ own method). The second stage consisted of measuring the emission of gases released by binders subjected to pyrolysis (the so-called flash pyrolysis), which simulated the effects occurring on the boundary: liquid metal/molding sand. The gases emitted from the tested binders indicated that, in both cases, the emission of harmful and dangerous substances (e.g., benzene) occurs, but, of the given binder systems, this emission was lower for the phenolic-ester no-bake binder. The obtained emission factors of BTEX substances show higher values for furan resin compared to formaldehyde resin; for example, the concentration of benzene per 1 kg of binder for furan no-bake (FNB) was 40,158 mg, while, for phenol-formaldehyde no-bake (PFNB), it was much lower, 30,911 mg. Thus, this system was more environmentally friendly.
To test the hypothesis that drought predisposes trees to insect attacks, we quantified the effects of water availability on insect attacks, tree resistance mechanisms, and mortality of mature piñon ...pine (Pinus edulis) and one-seed juniper (Juniperus monosperma) using an experimental drought study in New Mexico, USA.
The study had four replicated treatments (40 × 40 m plot/replicate): removal of 45% of ambient annual precipitation (H2O−); irrigation to produce 125% of ambient annual precipitation (H2O+); a drought control (C) to quantify the impact of the drought infrastructure; and ambient precipitation (A).
Piñon began dying 1 yr after drought initiation, with higher mortality in the H2O− treatment relative to other treatments. Beetles (bark/twig) were present in 92% of dead trees. Resin duct density and area were more strongly affected by treatments and more strongly associated with piñon mortality than direct measurements of resin flow. For juniper, treatments had no effect on insect resistance or attacks, but needle browning was highest in the H2O− treatment.
Our results provide strong evidence that ≥ 1 yr of severe drought predisposes piñon to insect attacks and increases mortality, whereas 3 yr of the same drought causes partial canopy loss in juniper.
The present study assessed the effect of sandblasting and silanization on resin cement bond strengths to CAD/CAM resin blocks. Twenty four blocks (KATANA AVENCIA BLOCK) were divided into two resin ...cement groups (PANAVIA V5 PV5 and PANAVIA SA CEMENT HANDMIX PSA), and further divided into four subgroups representing different surface treatment methods: no treatment (Ctl), silanization (Si), sandblasting (Sb), and Sb+Si. After resin application, microtensile bond strengths (μTBSs) were measured immediately, 1, 3 and 6 months after water storage. In addition, surfaces resulting from each of the treatment methods were analyzed by scanning electron microscopy (SEM). Three-way analysis of variance revealed a statistically significant effect for the parameters ‘surface treatment’ (p<0.001, F=370), ‘resin cement’ (p<0.001, F=103, PSA<PV5), and ‘water aging’ (p<0.001, F=18). Control treatment yielded significantly lower μTBS values compared to other treatment subgroups (p<0.001). The highest bond strength was achieved with Sb+Si treatment. SEM revealed that sandblasting roughened surfaces.
In the present work, biophenol and furfural‐based resol resin was synthesized and utilized for the very first time to cure styrene butadiene rubber (SBR). The reaction was studied over a range of ...times, temperatures, pH, and furfural to biophenol ratios to fix the optimum conditions. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy revealed the functional groups and chemical structure of the synthesized resin, respectively. An exothermic peak for the resin curing appeared at 143°C in the differential scanning calorimetry thermogram of the resin. Then, the biophenol‐furfural resin was utilized for the curing of SBR. The synthesized resin increased the tensile strength of the raw rubber from 0.20 ± 0.01 MPa to 1.22 ± 0.10 MPa at 10 phr loading, and the crosslink density was 2.56 × 10−5 mol/mL. The activation energy for curing SBR containing 10 phr resin was 97 kJ/mol. The storage modulus of the resin‐cured compound was improved. The glass transition temperature of the raw SBR was also shifted from −43.8 to −42.3°C when 10 phr resin was used for the curing. Hence, for the first time, this work reported the utilization of biophenol‐biosourced furfural resin to cure rubbers.
The carboxy groups abundantly and densely present on 2,2,6,6-tetramehylpiperidine-1-oxyl radical (TEMPO)-oxidized cellulose nanofibers (TEMPO-CNFs) have been chemically modified to prepare resin ...composites with high thermal dimensional stability. A primary-amine-terminated polyalkylene glycol (PAG) with number-average degree of polymerization of 2222 was reacted with the carboxy groups in the TEMPO-CNFs through amide bonds at PAG amidation degrees of 22%, 44%, and 76% of the carboxy groups in the TEMPO-CNFs by changing the reaction conditions. These surface PAG-amidated TEMPO-CNFs were nanodispersed in methyl ethyl ketone (MEK), mixed with the polyurethane acrylate monomer, and PAG-amidated TEMPO-CNF/polyacrylate resin composites were prepared by ultraviolet-light curing. When PAG-amidated TEMPO-CNFs with amidation degree of 44% were used, the tensile modulus and thermal dimensional stability of the PAG-amidated TEMPO-CNF/polyacrylate resin composite remarkably improved. This was because the TEMPO-CNF elements were homogeneously distributed in the polyacrylate resin matrix, which was confirmed by atomic force microscopy observation and percolation theory. In contrast, when epoxy resin was used as the composite matrix, the above PAG-amidated TEMPO-CNFs did not have high thermal dimensional stability. However, when a dual surface-modified TEMPO-CNF sample containing phenyl amides and PAG-ammonium/carboxylate salt structures at amidation and amine/carboxylate salt formation degrees of 80% and 6% of the carboxy groups in the TEMPO-CNFs, respectively, the thermal dimensional stability of the neat epoxy resin remarkably improved. Thus, the carboxy groups on the TEMPO-CNF surfaces have to be suitably modified, such as by PAG amide or phenyl amide/PAG-ammonium salt dual structures, depending on the matrix resin used.
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•HPE-GO has been prepared as an efficient and all-purpose modifier for epoxy resin.•HER provides strong interfacial bonding between GO and epoxy matrix.•HPE-GO/EP composites exhibit ...superior mechanical and thermal properties.
Despite great efforts have been made on epoxy resins modification, development of additives that can be used to efficiently and universally modify epoxy composites remains a challenging task. Herein, graphene oxide (GO) sheets were covalently linked with hyperbranched epoxy resin (HBPEE-epoxy) to form HBPEE-epoxy functionalized GO (HPE-GO), which was then incorporated into epoxy resin (EP) matrix to achieve efficient and all-purpose enhancement of the properties of EPs. Compared with unmodified GO sheets, the functionalized HPE-GO sheets were better dispersed and exhibited better interfacial compatibility with the epoxy matrix, and consequently, the mechanical and thermal properties of HPE-GO/EP composites improved significantly compared to unmodified GO/EP composites. The tensile strength, flexural strength, impact strength, and fracture toughness (KIC) of EP composites containing 0.5 wt% HPE-GO increased by 65.0%, 36.2%, 259.1%, and 178.9%, respectively, compared with those for the neat EP. The storage modulus (E'), glass transition temperature (Tg), and thermal stability (T5%) also showed modest improvements. Furthermore, the HPE-GO/EP composites exhibited optimal thermal conductivities and thermal expansion properties, while maintaining higher volume resistivities compared with GO/EP composites. The results of this study support that HPE-GO is a promising, all-purpose modifier for EPs.
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