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Abstract. Ternary composites of rigid polyurethane foam (RPUF)/glass fiber/silica as well as RPUF/glass fiber have been fabricated from glass fiber, silica, polymeric 4,4'-di-phenylmethane diisocyanate (PMDI) and polyol using HFC 365mfc as blowing agent. Foam formation kinetics, morphology, thermal conductivity, glass transition temperature, decomposition temperatures as well as the mechanical strengths of the foam have been studied. With the addition an increasing amount of glass fiber cream time, rise time, gel time, tack free time, density, compression strength, thermal conductivity (k) monotonically increased while the glass transition temperature showed a maximum at 2%. At constant glass fiber content (2%), addition of silica further increased the process times, density and compression strength while the T^sub g^ and thermal decomposition temperature showed a maximum at 3% silica. The k value of RFUF/glass fiber composite decreased with the addition of silica up to 3%, where it was even lower than the virgin RPUF. However, beyond the content k value increased. Overall, the variation of k value with silica content showed identical tendency with cells size and closed cells content.
Keywords: polymer composites, polyurethane rigid foams, functionalized silica, physical properties, thermal properties
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1. Introduction
Polyurethanes (PU) are typically formed by polyaddition reactions of isocyanates with polyols. Depending on the formulation, a broad property spectrum from elastomer to rigid foams are easily designed and synthesized [1-3]. Consequently a myriad of products such as foams, coatings, adhesives, sealants, elastomers, and thermoplastics are obtained and applied in the area of apparels, furnishings, automotive, building, electronics, marine, medical and others with an annual production over 18 million tons 2015 [4-6]. Among the PU products, rigid polyurethane foams (RPUFs) are excellent thermal insulating materials which are widely applied in refrigerators, freezers, hot water tank, liquid natural gas (LNG) cargo, sandwich and roofing panels, and various spray-in-place foams for insulation and sealing in complex cavities [7-9]. The essential feature of RPUF is that the cells are closed and blowing agents are entrapped within the cells [1]. This requires the use of multifunctional (2.5-3.2) polymeric MDI rather than MDI which is strictly di-functional. Consequently networks are formed in the RPUF.
The blowing agents should dissolve well in the reaction mix and remain in the closed cells as a gas which provides...