Masaki Shimbo

Mechanical relaxation mechanism of epoxide resins cured with diamines

Abstract The mechanism of mechanical relaxation, which is observed between 50° and 90°C in epoxide resins cured with aromatic and alicyclic diamines, has been investigated by comparing dynamic mechanical properties and chemical structures of these networks. This relaxation is denoted here as the α′ relaxation. The occurrence of the α′ relaxation depends on the existence of p -phenylene groups, and is independent of the degree of cure in the cured epoxide resins. Moreover, the intensity of the α′ relaxation increases linearly with increasing the concentration of p -phenylene groups in the networks. From these results, it is concluded that the α′ relaxation of the cured epoxide resins is attributed to the motion of p -phenylene groups in the network structures.

Internal stress of epoxide resin modified with spiro ortho-ester type resin

Bisphenol-A type epoxide resin modified with various amounts of spiro ortho-ester (SOE) resin was cured with an imidazole. Internal stress of the modified systems decreased with increasing fraction of SOE resin in the cured resins. In particular, a drastic reduction of the internal stress was observed in the systems modified with more than 33 mol% SOE resin. In addition, heterogeneous structure was observed with modifier content over 33 mol%, and the elastic modulus of these systems decreased step-wise with increasing ambient temperature. On the other hand, the systems in which the modifier content was less than 20 mol% had homogeneous structure and thus the modulus was considerably higher than that of the former systems. Consequently, it was concluded that the drastic reduction of the internal stress in the systems modified with more than 33 mol% SOE resin depends on the low elastic modulus caused by the formation of heterogeneous structure.

Frictional behaviour of cured epoxide resins

Abstract The friction mechanisms for sliding between dicarboxylic-acid-cured epoxide resins and stainless steel were investigated by monitoring the changes in the coefficient of friction and the geometry of the sliding surfaces in the glassy, transition and rubbery regions of the cured resins. In the glassy region, a constant value of the friction coefficient was obtained in spite of the variation in contact pressure. A trace of shearing fracture was observed on the sliding surfaces, and a linear relationship existed between the friction coefficient and the shear modulus of the cured resins. In the transition region, the maximum values of the friction coefficient were observed at the glass transition temperatures of the cured resins. The maximum value increased as the magnitude of the damping of these resins increased. In this region it was found that the softened polymer adhered to the metal surface and was also deformed by the movement of the metal specimen. In the rubbery region, the friction coefficient remained constant in spite of the variation in contact pressure. It was shown that a good correlation exists between the friction coefficient and the concentration of network chains.

Effect of the introduction of methoxy branches on low-temperature relaxations and fracture toughness of epoxide resins

Abstract Some epoxide resins with or without methoxy branches were cured with an aromatic diamine. A well defined relaxation was observed near room temperature for all cured resins with methoxy branches, independent of the epoxide-resin structure. The relaxation was denoted here as the β′-relaxation. It is suggested that the β′-relaxation can be attributed to suppression of the motion of the hydroxy ether group due to the interaction between this group and the methoxy branch. The effect of the β′-relaxation on the fracture toughness of cured epoxide resins was studied by comparing the stress intensity factor K c of a spiro-ring type epoxide resin containing a methoxy branch with that of a bisphenol A type resin. The value of K c in the former system is considerably higher above the β′-relaxation temperature than that of the latter system. This is explained by the increase in the plastic deformation region at the crack front with increase in temperature caused by the presence of the β′-relaxation.

Mechanical properties of diallyl phthalate resins co-cured microheterogeneously with vinyl monomers having long-chain alkyl groups

SummaryDiallyl phthalate(DAP) was co-cured with vinyl monomers having long-chain alkyl groups, including vinyl laurate(VL), dioctyl fumarate(DOF), lauryl methacrylate(LMA), and stearyl methacrylate(SMA) with the intention of the improvement in mechanical properties of commercially important DAP resins. Thus the elongation and fracture energy increased with an increase in the mole fraction of comonomers and their extents were enlarged in the order VL < DOF < LMA < SMA, although a reverse tendency was observed for the tensile strength; in particular, LMA and SMA as comonomers showed a remarkable effect. These results are discussed in detail by considering the copolymerizability of DAP with comonomers and, moreover, the formation of microgel in microheterogeneous copolymerization systems.

Mechanical and dielectric relaxations of poly(hydroxy ethers): 1. Low-temperature relaxations

Abstract Mechanisms for the low-temperature relaxations were investigated for poly(hydroxy ethers) prepared by the polyaddition reaction of diglycidyl ethers with diphenols. Two relaxations, denoted β and β′, are observed at −70 and +40°C (for a frequency of ∼ 1 Hz), respectively. It is revealed by comparing the mechanical relaxation with the dielectric relaxation that the β relaxation is a complex relaxation, that is, the overlap of the relaxation of hydroxy ether segment with that of other parts in the polymer chain, and that the β′ relaxation is due to the motion of the phenylene group in the polymer chain. In the acetylated poly(hydroxy ethers), the relaxation of the hydroxy ether segment disappears and a new relaxation due to the motion of the acetylated segment appears near 0°C. This new relaxation is superimposed upon the β′ relaxation.

Mechanical relaxation properties of spiro-type epoxide resins cured with acid anhydrides

Abstract Low-temperature relaxation behaviour has been investigated for a bisphenol-A type and three spiro-type epoxide resins cured with acid anhydrides. In the spiro-type resin systems, one new relaxation, denoted here as the β′ relaxation, is clearly observed near room temperature. It is suggested that the β′ relaxation is related to the motion of p -phenylene group adjacent to the spiro ring. The impact strength of epoxide resin systems that show the β′ relaxation is considerably higher than that of other cured systems and is proportional to the intensity of the β′ relaxation. Consequently, it is concluded that the existence of the room-temperature relaxation such as the β′ relaxation is associated with increased toughness of cured epoxide resins.

Fracture behaviour of toughened epoxy resins cured with N,N′-dimethylethylenediamine

Abstract Two series of toughened epoxy resin systems, which are models of matrix resins for use in carbon fibre reinforced plastics, were prepared. Evaluations of the cured epoxy resins, measuring fracture toughness, impact properties, tensile properties and dynamic mechanical properties were conducted. The correlations between these properties and the apparent concentration of network chains in the resins, v , were investigated and the fracture surfaces were examined with a scanning electron microscope. The superior toughness of these resin systems was obtained without considerable loss in modulus. Unified maximum peak was observed in the plots of Izod impact strength, where the v value of the cured resins was increased.

Internal stresses in UV-cured epoxide resin coatings.

紫外線硬化エポキシ樹脂塗膜の内部応力をレ-ザー変位計を用いて被塗布体の変位を測定することによって求めた. この方法では, 塗膜の硬化及び冷却の両過程における内部応力を精度よく測定することができた. 塗膜の内部応力は, 紫外線照射に伴う塗膜温度の上昇の少ない系ほど低下した. これは, 硬化後の冷却過程における塗膜の冷却収縮の低下に起因することが示された. また, 内部応力は塗膜の膜厚の増加に伴って減少した. この内部応力の膜厚依存性は, 硬化過程では紫外線硬化系に特有な表面層と内部の硬化度の不均一性の面から議論され, 冷却過程では塗膜温度の不均一性の面から議論された. すなわち, 硬化過程では表面層の硬化収縮はまだ硬化していない内部層によって緩和され, 冷却過程では内部層の冷却収縮が先に冷却された弾性率の高い表面層によって抑制されるため, 内部応力が低下するものと考えられた.

Curing Mechanism of the Epoxide Resins

構造を異にする2種類のエポキシ樹脂を, 脂肪族および芳香族アミン, ポリアミドおよび酸無水物を用いて硬化し, その硬化の機作を動力学的性質の面から検討した。エポキシ樹脂のような接着剤の結合強さは, 試験条件を細かく規定した工業的試験法によって測定され, その値は再現性はあるが, 接着強さの比較値を得るにすぎぬものとされていた。本研究ではこのような接着強さのうち, 引張せん断強さは凝集破壊領域では橋かけ間分子量もしくは弾性率の関数となることを明らかにした。この結果から, 接着強さの非破壊試験も可能と考えられる。はく離強さについては, 硬化物のガラス転移温度がはく離の試験温度に一致したときに極大値をとることを示し, しかも凝集破壊領域から界面破壊領域に移行するときにその極大値が現われることを上記樹脂一硬化剤の多くの系について示した。