| Polyurethane rigid foam(RPUF)can be used as pipe insulation material,has the advantages of aging resistance,corrosion resistance,cold resistance,and other advantages.Compared with other insulation materials such as polystyrene,it can be used for a long time and does not need to be replaced regularly.But at present the most popular or expanded polystyrene,extrusion polystyrene and mineral cotton fabrics.EPS dominates all other thermal insulation materials,controlling more than 45-50%share in the thermal insulation materials market,featuring low prices,excellent product performance and ease of processing.It is because of the shortcomings of high production cost,high foaming temperature and poor dimensional stability of RPUF that the development and market of RPUF as insulation materials are inhibited.In this paper,a kind of polyurethane rigid porous foam material was prepared by one step foaming method with RPUF as the substrate,unfoamed polystyrene microbeads(EPS)as the reinforcing material,HCFC-141 b as the physical foaming agent and silicone oil as the foaming agent.Monitoring foaming temperatures in different areas of unfoamed EPS modified RPUF with different contents,and drawing3 D temperature maps;The optimum scheme was determined by the index of aperture distribution,density,thermal conductivity,compressive strength and dimensional stability,and was characterized and analyzed.The density,thermal conductivity,compressive strength and water absorption of composite foam materials were compared.After the aging test,its performance changes,compression strength,dimensional stability,water absorption,thermal conductivity and so on,and its life prediction.The specific research is as follows:1.Multiple ordinary differential equations in the foaming process model of rigid polyurethane were used to solve the problem,and the change of foaming temperature over time was predicted.The maximum temperature range of RPUF with foaming thickness of 30 mm and 50 mm was determined to be 160 ℃-180 ℃.Then,PT100 probe temperature sensor was used to observe the changes of internal foaming temperature of RPUF modified by unfoamed EPS with different contents over time.The results of 3D temperature distribution diagram showed that: EPS content is 30%,mixed into 2.5g silicone oil 8805,1.8g deionized water,0.65 g TMR-2,1.9gdmcha,0.15 g PMDETA,18 g HCFC-141 B and then added into the isocyanate number 1.05 black and white mixture.After stirring at 1400 RPM for 30 s,cure at room temperature for 24 h.The central foaming temperature of the composite material decreased by 27%from 155 ℃ to 113 ℃.It was found that the higher the EPS content was,the temperature in the inner core region showed a linear downward trend,and the faster the temperature decline rate.Through SEM analysis,it is found that the foaming degree of EPS in RPUF depends on the foaming temperature of composite materials,and the optimal content is 30% EPS particle foaming diameter is 1.6mm.The relationship between foam rising speed and time showed that the maximum rising speed was 1.5 mm/s at 100 s,which was 50% lower than that of pure RPUF,indicating that the content of the admixture hindered the molecular mobility,also reduced the reaction between hydroxyl group and isocyanate,increased the gel time and slowed down the foaming process.Therefore,the foaming temperature of RPUF can be regulated by controlling different contents of unfoamed EPS.2.The effect of adding 0~50% unfoamed EPS on the performance of polyurethane rigid foam was studied,and the optimal unfoamed EPS content was determined by the optimization variable method.The heat flow curve of unfoamed EPS was analyzed by DSC,and the absorption peak obtained proved that the phase transition of pentane isomer and EPS had a beneficial effect on the reduction of foaming temperature.Its compressive strength increases 130% at room temperature,elastic modulus increases 55.8% at-30 ℃,and compressive strength increases 66.6%.The specific plug-ins developed for measurement using Image J also provided quantitative information on other parameter characteristics,including the bubble size distribution in foaming direction,the average bubble size,and the bubble structure.It was determined that the surface of the packing provided many nucleation points for bubble formation.The optimal content foam size was reduced by 19.8% compared to the pure RPUF,and the average bubble size was reduced by 9.3%.It was found that the increase of density by 50% was the main reason for the decrease of thermal conductivity and insulation capacity.Other reasons included the decrease of pore diameter,the thinning of pore wall,the acceleration of diffusion of gas with low thermal conductivity and the high thermal conductivity of EPS itself.The dimensional stability of EPS modified RPUF composites was tested: the length size change rate increased by 0.25%,width size change rate increased by 3.93% and foam thickness size change rate increased by 13.1%,which solved the problem of poor dimensional stability of polyurethane rigid foam made by the factory.Overall consideration,30%EPS modified polyurethane rigid foam not only gives consideration to light density,but also maintains good thermal conductivity,good obturator rate and water absorption,and reduces the production cost.3.A 10-week aging experiment was conducted on EPS modified RPUF foam,and it was found that the percentage of mass samples increased from 9.84% to 21.86%when the temperature of 140 ℃ or above was aged for 10 weeks.As RPUF composite foam mainly suffered from thermal degradation reaction,The main reason is that the C-N bond in carbamate and the C-O bond connected with carbamate and methylene in foam are broken.The weight loss is only 2.39 % after aging at 80 ℃ for 10 weeks.After 10 weeks of aging,the thickness decreased by 4.85% at 140 °C,8.314% at 150°C and 10.7% at 160°C.After 10 weeks of aging,the compressive strength decreases at40 ℃ to 150 ℃,with the fastest decreasing rate at 150 ℃.The compressive strength increased slightly to 0.331 MPa and 0.353 MPa in the first 4 weeks at 40 ℃ and 80 ℃.After the freeze-thaw cycle for 1 week,the thermal conductivity increases significantly,and then the thermal conductivity increases slowly and has little change,reaching0.027 W /(m · K)and 0.034 W /(m · K).Pore size and wall thickness are the main factors affecting the thermal conductivity,resulting in serious leakage of low thermal conductivity gas.Compared with the compression strength of pure RPUF in acid and alkali environment,the compression strength of pure RPUF increases by 11.6% and9%.Due to the corrosion of pure RPUF,the volume and mass will be reduced to different degrees.The destruction of foam leads to the increase of pore connectivity,which leads to the water in soil entering the bubble more easily. |
