It is common knowledge that the hard segment in polyurethane extensively influences the physical properties, therefore the aim of this study is to clarify the improvement effect of fracture toughness of cured epoxy resins added polyurethanes having hard segment.Polyurethaneprepoymors having hard segment were synthesized with two kinds of macroglycols (Mn=2000, Polyoxypropylene glycol: PPG, Polycarbonate glycol: PCG), diisocyanate (MDI) and 1,4-Butanediol (1,4-BD), and at the final step the respective polyurethaneprepolymers were reacted with bisphenol-A type epoxy resin with monofunctional hydroxyl group.The epoxy resin terminated polyurethenes (ETPU-Btype) were added to typical bisphenol-A type epoxy resin and cured by adipic acid dihydrazide (ADH).The relationship between properties of cured epoxy resins and hard segment was investigated by comparing with the properties of non-hard segment type (ETPU-N type).All ETPU-B type showed higher improvement effect than ETPU-N type.Regarding bending modulus PPG-B system (P2B system) and PCG-B system (C2B system) showed the higher modulus at over 30phr than the corresponding ETPU-N types.It was observed that C2B system showed the higher fracture toughness than C2N system and kept the relative high value even at 50phr.Similarly P2B system was superior to P2N system, but the fracture toughness at 50phr was observed a significant decrease.The results of scanning electron microscopy (SEM) indicated micro phase separation structure in all ETPU.ETPU-B type presented the uniform distribution of finer particles than ETPU-N type.It can be concluded from the results that the systems which showed high fracture toughness indicated micro phase separation with the finer particles.This suggested that hard segment in polyurethane contributed to the formation of valuable morphology.

View full abstract

A new form of dismantlable adhesisve technology has been developed.This is a revolutionary development in the construction industry, which makes it possible for the bonded compound of building materials to be separated by the simple application of heat after use and therefore to boad apted to recycling.Heating over 100℃ causes the adhesive polymer to soften, and at the same time the thermally expansive particles expand, resulting in loss of bond strength and thus enabling their easy separation.This article describes the dismantlement behavior of joints having the adherends of steel plate and these materials (cement board, plaster board, and plastic board).At the elastomer type dismantlable adhesive, the weight fraction of thermally expansive particles from 5 to 15% is suitable for both bond strength and dismantlement.The bond strength of joints could not decrease after durability test at 60℃ for 30days, and then it was separated easily by infrared rays heating at 150～180℃ or 2 minutes.At this technology, manufacturing is equal to conventional adhesives, and time of heating for dismantlement is quite short, so that it is efficient for not only performance (adhesive and dismantlement), but also manufacturing and cost.

View full abstract

The aim of this study is to characterize the adhesive properties of the toughened epoxy resins blended with pre-formed polyamide-12 particles in comparison with conventional approach using core-shell rubber particles.Dicyandiamide (DICY) cured diglycidyl ether of bisphenol-A was used as the base epoxy resin.T-peel adhesive strength of the toughened resin including 20phr polyamide-12 particles was about 3-times as strong as that of the non-modified resin.In the case of rubber toughening, however, the improvement in adhesive strength tended to saturate to a certain level, even with improving in the resin toughness.Polyamide particles embedded in epoxy resin matrix were fractured after the large plastic deformation during the peel process, which suggested the crack bridging mechanism by the particles worked behind the crack tip.The crack-wake toughening mechanism using the thermoplastic polymer particles would avoid the constraint on the plastic deformation by the existence of aluminum adherends and be promising to utilize the bulk resin toughness even the case of thin bond thickness of resin layer.This would not be the case of rubber toughening which works in front of the crack tip.

View full abstract