Preparation Of Rigid Polyurethane Foam With High Performance And Investigation On Its Flame Retardancy

Rigid polyurethane(PU) foams have a remarkably broad range of applications in kinds of industries due to their desirable properties such as low density, fine diffuse barrier properties, excellent shock absorption, high tear strength, good cellular stability and flexible processing methods as well as convenient molding to construction.Compressive strength and tensile strength are key physical properties of materials to withstand strain in application. However, as for structural and semi-structural applications, rigid PU foams still present some disadvantages, such as low stability and low mechanical strength. It needs adding reforcing fillers into PU matrix in order to solve the above problems. On one hand, the reforcing filler can enhance the abrasion resistance, physical mechnical propeties and strength of PU composites. On the other hand, adding reforcing filler into PU matrix can reduce the cost and save the energy as well. With many advantages such as nano-structure, abundant resource, low price and easy application as well, montmorillonite can remarkably improve tensile strength of composites, but slightly affect the compressive modulus of composites, thus attracted many interests of researchers.It is well known that water easily reacts with isocyanate group to generate polyurea and carbon dioxide with the release of exothermic reaction heat. In this thesis, it is found for the first time that organoclay itself can act as blowing agent of PU foams due to its boundwater intercalated between the internal layers of organoclay. So we developed a novel method to prepare PU foams/organoclay nanocomposites with greatly simultaneously improved compressive and tensile strengths. Analysis indicates that mechanical properties of composites are closely relative to the chemical structure and cell structure of materials.Because of the poor compatibility between montmorillonite and polymer matrix, the resultant polymer composites have low performance. So a great number of researches have been done to surface-modify montmorillonite. Meanwhile, PU releases a lot of toxic gas such as carbon monoxide and hydrocyanic acid etc., greatlythreating the public safety. The improvement of flame retardancy of rigid PU foams has become a key factor to its continuous application in the future. In order to prepare PU composites with higher performance and investigate the effect of surface-modifiers of clay on the mechanical properties, thermal stability and flame retardancy of PU composites, we choose three different organoclays ODTMA-MMT, ODPA-MMT and DDA-MMT to prepare PU composites respectively. It is found DDA-MMT can be partially exfoliated in the PU matrix due to the reaction between free NH2- functional groups in DDA-MMT and isocyanate groups of the PU matrix, and the corresponding nanocomposite has the smallest cell size.Adding organoclys into PU matrix can enhance the thermal stability and flame retardancy of PU composites among which PU/DDA-MMT composite has highest mechanical properties, thermal stability and flame retardancy. The morphology (including the dispersion state of organoclay in the PU matrix and the cell structure of rigid PU foams/organoclay composites) of rigid PU foams/organoclay composites is greatly depended on the nature of organoclays, and the nature of organoclays is lied on their surface modifiers.