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The effect of the chemical structure of low‐profile additives on the curing behavior and chemorheology of unsaturated polyester resin
Author(s) -
Lee DaiSoo,
Dae Han Chang
Publication year - 1987
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760271307
Subject(s) - materials science , curing (chemistry) , styrene , polyester resin , isobutylene , differential scanning calorimetry , composite material , monomer , natural rubber , polyester , gelcoat , polymer chemistry , copolymer , polymer , synthetic resin , physics , thermodynamics
An experimental study was conducted to investigate the effect of the chemical structure of low‐profile additives on the curing behavior and chemorheology of unsaturated polyester resin during isothermal cure. For the study a general‐purpose unsaturated polyester resin was cured in the presence of t‐butyl perbenzoate as Initiator. The curing behavior of the resin was investigated using differential scanning calorimetry (DSC). Three different thermoplastic low‐profile additives were used, namely poly(vinyl acetate) (PVAc), poly(styrene‐co‐butadiene), which is also known as KRATON DX‐1300, and dehydrochlorinated Isobutylene/isoprene copolymer, often referred to as conjugated diene butyl (CDB) rubber. Each of the these additives, about 30 weight percent, was first dissolved in styrene. The solution was then mixed with unsaturated polyester resin and CaCO 3 . The CaCO 3 particles helped stabilize the emulsions consisting of resin and KRATCN, and of resin and CDB. For each resin formulation, a series of isothermal DSC runs were made at various levels of cure pressure. It was found that for all three low‐profile resins investigated, the final degree of cure went through a maximum as cure pressure was increased from atmospheric to 6.21 MPa (900 psi). We have observed evidence that in the presence of an initiator generating free radicals, the unsaturated double bonds in the KRATON and CDB undergo grafting reactions with the styrene monomers and unsaturated polyester resin, increasing the glass transition temperature of KRATON and CDB, to an extent which varies with the cure conditions employed. Both steady and oscillatory shearing flow properties were determined using a cone‐and‐plate rheometer. The rheological measurements indicate that the resin/CaCO 3 /KRATON and resin/CaCO 3 /CDB systems give rise to gel times shorter than the resin/CaCO 3 /PVAc system. It is concluded that both KRATON and CDB are more effective, both for enhancing the rate of cure of unsaturated polyester resin and imparting impact properties to the cured composites, than those thermoplastic low‐profile additives that contain neither unsaturated double bonds nor a chemical structure that has rubber‐like properties in the solid state.