Polyurethane Foam Bubble Pore Structure And Mechanical Properties Of Relations

Polyurethane foam is a kind of polymer foam materials. Its mechanical performances are functions of its chemical structure, density, etc, and its cellular structure. Mean cell diameter and its distribution, fraction of close cells and film thickness are three main parameters describing the characteristics of cellular structure. In this thesis, molded foaming and free foaming processes were employed to prepare rigid polyurethane foam with different cellular structure by varying formulations and processing conditions. 2D image analysis methods and some devices were employed to determine mean cell diameter and its distribution, fraction of close cells and film thickness of these materials. Quasi-static compression tests and impact tests were performed to determine compressive strength, compressive modulus and impactive strength of these materials.Effects of silicone surfactant types and concentrations, components of catalysts, and rotation speed of blender on cellular structure of rigid polyurethane foams were studied. It is indicated that, increasing concentration of silicone surfactant generally leads to decreased average cell diameter, except that its concentration is beyond its solubility in polyol ingredient resulting in surfactant aggregating or foam collapse. Triethanolamine solely acting as catalyst of polyurethane foam system generally leads to lower fraction of close cells due to lower gelling speed, while triethanolamine-caprylic tin composite catalyst always leads to fraction of close cells up to 100 percents. Varying catalyst component leads to different average cell diameter of foam. Effect of rotation speed of blender is more remarkable in physical foaming system than in chemical foaming system, and mean cell diameter of foam decreases with increasing rotation speed of blender.A method based on 2D image of cellular structure obtained by scanning electron microscope was established to get mean cell diameter of foam. We derived mean cell diameter from mean section area of cells on one SEM image of cellular structure. This method contains three primary parts: pretreatment of image, computerized measuring of cell section area, and conversion from 2D measuring results to real 3D cellular structure parameter.Relationships between cellular structure and mechanical performance of high density (180 kg/m~3) RPUF were researched. It is indicated that RPUF's compressive strength and Young's modulus increase with increasing mean cell diameter or fraction of close cells, and impactive strength decreases with increasing mean cell diameter or fraction of close cells. Mechanisms by which RPUF's compressive performance is dominated proposed by Smits, and Gibson-Ashby formula were used to reasonably interpret and predict the relationshipsbetween high density(180 kg/m3) RPUF's cellular structure(such as mean cell diameter, fraction of close cells and film thickness) and mechanical performance(including compressive strength, Young's modulus, and impactive strength).