Mechanical characterization and morphology of carboxyl randomized poly(2-ethyl hexyl acrylate) liquid rubber toughened epoxy resins

Rubber-Composite-Nanoparticle-Modified Epoxy Powder Coatings with Low Curing Temperature and High Toughness

In this study, a rubber-composite-nanoparticle-modified epoxy powder composite coating with low curing temperature and high toughness was successfully fabricated. The effects of N,N-dimethylhexadecylamine (DMA) carboxy-terminated nitrile rubber (CNBR) composite nanoparticles on the microstructure, curing behavior, and mechanical properties of epoxy-powder coating were systematically investigated. SEM and TEM analysis revealed a uniform dispersion of DMA-CNBR in the epoxy-powder coating, with average diameter of 100 nm. The curing temperature of the epoxy-composite coatings had reduced almost 19.1% with the addition of 1phr DMA-4CNBR into the coating. Impact strength tests confirmed that DMA-CNBR-modified epoxy-composite coatings showed significant improvements compared with the neat EP coating, which was potentially attributed to the nanoscale dispersion of DMA-CNBR particles in epoxy coatings and their role in triggering microcracks. Other mechanical properties, including adhesion and cupping values, were improved in the same manner. In addition, thermal and surface properties were also studied. The prepared epoxy composite powder coating with the combination of low curing temperature and high toughness broadened the application range of the epoxy coatings.

Mechanical properties of epoxy resin toughened with cornstarch

We investigated the effect of starch modification on the mechanical properties of phenolic epoxy resin (EP). Corn starch admixture of 2.5, 5, 7.5, and 10 wt% were added into the EP. The tensile strength, elongation at break, and elastic modulus of different corn starch contents were compared. The containing of corn starch showed a positive effect on the toughness of the epoxy but showed little effect on strength when the additive content was less than 10 wt%. The strength and elastic modulus increased first and then decreased with the increase in starch content and reached their maximum values at a content of 2.5 wt%. The enhancement effect might be due to corn starch’s mechanical properties, dispersibility, and interfacial interaction. With the increase in starch content, starch granules quickly contact each other, causing self-aggregation sedimentation and a decrease in strength and elastic modulus. The scanning electron micrographs of the toughened EP specimens showed ductile failure because of the starch particles. The surface morphology of the blend resin specimens was full of staggered and stepped cracks caused by the shearing damage, which is shown by obvious plastic fracture characteristics with plastic deformation ability. The initiation of micro-cracks in the EP matrix was induced by the incorporation of starch particles, which caused localized stepped shear damage in the matrix. More energy would be absorbed during this process, and the toughness of the EP would be enhanced. It is recommended that the best corn starch content should be 2.5 wt% to obtain excellent strength and good toughness.

Synthetic Light-Curable Polymeric Materials Provide a Supportive Niche for Dental Pulp Stem Cells

Dental disease annually affects billions of patients, and while regenerative dentistry aims to heal dental tissue after injury, existing polymeric restorative materials, or fillings, do not directly participate in the healing process in a bioinstructive manner. There is a need for restorative materials that can support native functions of dental pulp stem cells (DPSCs), which are capable of regenerating dentin. A polymer microarray formed from commercially available monomers to rapidly identify materials that support DPSC adhesion is used. Based on these findings, thiol-ene chemistry is employed to achieve rapid light-curing and minimize residual monomer of the lead materials. Several triacrylate bulk polymers support DPSC adhesion, proliferation, and differentiation in vitro, and exhibit stiffness and tensile strength similar to existing dental materials. Conversely, materials composed of a trimethacrylate monomer or bisphenol A glycidyl methacrylate, which is a monomer standard in dental materials, do not support stem cell adhesion and negatively impact matrix and signaling pathways. Furthermore, thiol-ene polymerized triacrylates are used as permanent filling materials at the dentin-pulp interface in direct contact with irreversibly injured pulp tissue. These novel triacrylate-based biomaterials have potential to enable novel regenerative dental therapies in the clinic by both restoring teeth and providing a supportive niche for DPSCs.

Bio-based silica-reinforced caprolactam-toughened epoxy nanocomposites

In this work, industrially valuable and versatile nylon 6 precursor material caprolactam has been used as a toughener for diglycidyl ether of bisphenol A epoxy resin (caprolactam epoxy (CPE)) along with glycidyl-functionalized bio silica (GRS) derived from rice husk, which was used as a reinforcement to obtain hybrid nanocomposites with improved properties. Caprolactam (20 wt%) and epoxy (80 wt%) have been reinforced with varying weight percentages (0.5, 1.0 and 1.5 wt%) of GRS cured with diaminodiphenylmethane and characterized using different analytical techniques. Data obtained from mechanical studies indicate that the value of tensile strength, flexural strength and impact strength of 1.5 wt% GRS-reinforced caprolactam-toughened epoxy blend composites were enhanced to 135, 77 and 162%, respectively, compared with those of neat epoxy matrix. Similarly, the values of glass transition temperature and char yield were enhanced to 21 and 22%, respectively, whilst retaining inherent surface and insulating behaviour. Data from morphological studies infer the homogenous and uniform distribution of GRS in the CPE hybrid nanocomposites. From the data obtained from different studies, it is suggested that the hybrid composite materials developed in this work have potential use as coatings, adhesives, sealants, matrices and composites for different industrial and engineering applications in the place of conventional epoxy composites for improved performance and enhanced longevity.

Toughening epoxy resins by modification with in situ polymerized acrylate copolymer composed of butyl acrylate and glycidyl methacrylate

Poly(butyl acrylate–glycidyl methacrylate) (PBG) was prepared by in situ polymerization of butyl acrylate (BA) and glycidyl methacrylate (GMA) and further used as a modifier to improve the comprehensive properties of the epoxy resin curing system. The modified resin system was based on diglycidyl ether of bisphenol, methyl tetrahydrophthalic anhydride, and tris(dimethylaminomethyl)phenol. The influence of copolymer composition on the mechanical properties, thermal performance, and phase behavior of the system was carefully examined. Results showed that the addition of PBG greatly improved the impact strength of the modified epoxy resin. When 15 wt% of the BA/GMA with a weight ratio composition of 7.5/7.5 was added to the epoxy, high-performance-modified epoxy resin was obtained.

Separação de fases induzida por meio de reação química no sistema éter diglicidílico do bisfenol A e piperidina com poli(metacrilato de metila)

O comportamento da separação de fases e da gelificação do sistema epoxídico, constituído pelo éter diglicidílico do bisfenol A (DGEBA) e a piperidina, modificado com poli(metacrilato de metila) (PMMA), foi estudado na faixa de temperatura de 60 °C - 120 °C. A concentração de PMMA e a temperatura de cura causam mudanças significativas na morfologia gerada. A massa molecular de PMMA provoca ligeiras mudanças para a observação da separação de fases e não afeta a velocidade da reação. O sistema modificado com PMMA mostra o efeito de retardação cinético e a velocidade de separação de fases é maior que a velocidade de polimerização.