SYNOPSISEffects of particle size on the mechanical and impact properties of cured epoxy resins are studied. This resin was filled with spherical silica particles prepared by hydrolysis of silicon tetrachloride. Particles were sorted into five kinds of different mean sizes in the range from 6-42 pm. A static flexural and tensile tests and an instrumented Charpy type impact test were carried out. Flexural strength, tensile strength, and impact-absorbed energy increased with a decrease in the particle size. Fractured surfaces were observed using a scanning electron microscope to clarify the initiation point of fracture. INTRODUCTIONThe drawback of epoxy resin is still "low toughness," i.e., cured epoxy resin is a rather brittle polymer that has poor resistance to cracking. This crack is derived from the internal stress generated by shrinkage in the cooling process from cure temperature to room temperature.In a series of investigations, 1-6 we have been able to reduce internal stress. For this purpose, the formation of a two-phase structure in which soft acrylic polymer particles were dispersed as domains (second phase) in the cured epoxy matrix was carried out. As a result, the effects of the domain size' and the domainlmatrix interaction 2-6 on the reduction of the internal stress were clarified.Many researchers 7-18 have reported that the addition of rigid filler particles is useful for toughening cured epoxy resin. Most of these studies were carried out using glass beads, but a few studies were made using irregularly shaped silica particles ranging from 60-300 pm in diameter.15 Recently, cured epoxy resin filled with irregularly shaped and spherical silica partides ranging in size from submicron to about * To whom correspondence should be addressed. CCC 0021-8995/92/071281-09$04.00 100 pm were used as encapsulating materials for integrated circuits.'s~20 In the previous articles, 21-23 the effect of particle size on fracture toughness was studied using such irregularly and spherical silica particles 22723 having different mean sizes in the range from 2 to about 50 pm.Mechanical and impact properties of the particles are also important for application of these materials. Some researchers have reported these properties using glass beads 13,15 or the above-mentioned larger, irregularly shaped silica particle^.'^.'^ In the previous articles, 24-26 effects of particle size on and impact properties26 were studied using the same irregularly shaped silica particles.In this study, subsequently, we report the effects of particle size on the mechanical and impact properties of epoxy resin filled with spherical silica. EXPERIMENTAL MaterialsSpherical silica particles (Excelica ML-801, Tokuyama Soda Co., Ltd.) were prepared as follows. Agglomarated Si02 was produced by hydrolysis of silicon tetrachloride through the following reaction: Subsequently, agglomarated SiOp was fused in a flame of hydrogen and oxygen; as a result, spherical particles were obtained. Particles were sorted into five groups by air separation. The mean ...

The occupied area (Am) of a sodium dodecyl benzene sulfonate molecule adsorbed on particles was measured by the soap titration method. The Am values are 214, 133, and 53 Å2 for poly(methyl acrylate) (I), poly(methyl methacrylate) (II), and polystyrene (III), respectively. For methyl metharylate‐styrene copolymer emulsions the additivity was established between the Am value and copolymer composition. Composite emulsion particles consisting of I/II, I/III, and II/III were prepared by seeded emulsion polymerization. For these emulsions the relationship between polymer composition at the surface layer calculated from the Am value and that in a particle calculated from the polymerization process was investigated. This relationship is remarkably affected by the order of polymerization, the hydrophilicity of polymer, the flexibility of the seed polymer, and the monomer addition method. The models of the morphology of these composite particles explain the results successfully.

SYNOPSISEffect of particle size on the mechanical properties of cured epoxy resins has been studied. Resin was filled with angular-shaped silica particles prepared by crushing fused natural raw quartz. These particles were sorted into six groups having different mean sizes ranging from 2-47 pm. Flexural and compressive moduli of the cured epoxy resin slightly decreased with decrease in the particle size of the silica, whereas tensile modulus slightly increased. Flexural and tensile strengths increased with decrease in particle size. Fractured surfaces were observed using scanning electron microscopy to clarify the initiation point of fracture.

No abstract

No abstract