Foaming Technology And Performance Of Silica Aerogel/polystyrene Composite Materials

Polystyrenecystosepiment is widely used in many fileds such as building,packaging,etc.due to its good heat insulation,low density and low price,which ranked No.2 in heat insulation materials.In order to reduce the thermal conductivity coefficient of polystyrene cystosepiment,introducing silica aerogel into the material can realize the aim by designing distribution of micro and nano pore in the microstructure.Silica aerogel has three-dimensional porous network porosity as high as 80-99.8%,coefficient of thermal conductivity 0.019W·m-1·K-1at room temperature,which is the best thermal insulation materials up to now.According to the heat conduction principle of thermal insulation composite,it was a feasiable method by analysing the structure of raw materials and designingof the cell structure.Tocombine the advantages of silica aerogel with nano pores and polystyrene cystosepiment with cell pores,controlled composite must be prepared firstly.Suspension polymerizationwas used to prepare the special composit,which included two liquid phases,one phase had deionized water,anhydrous sodium sulfate,4% polyvinyl alcohol,sodium dodecyl benzene sulfonic acid,hydroxy calcium phosphate solution the other phase was styrene,benzoyl peroxide,SiO₂ aerogel.Scanning electron microscopy showed that the polystyrene bead was dense and flat.With increasing of inorganic particles,interface of composite became more and more looser and appeared more pores accordingly.Externalzone of bead had loosened structure and higher porosity than internal zone.Gel permeation chromatography result show that with increasing of initiator number-average molecular mass increased firstly from 21591 g/mol to 30945 g/mol and laterdecreased to 17819 g/mol,and weight-average molecular weight increased firstly from 46118g/mol to 65317g/mol and later decreased to 38753g/mol.Composite was characterized by ultraviolet spectrophotometer.The results show that with increasingof particles the suspension polymerization reaction conversion rate decreased.The composites byintroducing of10vol%,15vol%,20vol% SiO₂ aerogel had corresponding to 89.12%,86.07% and 89.12% reaction conversion rate of composites respectively.The composites by Introducing 10vol%,40vol%,70vol% nano SiO₂ had corresponding to 92.93%,89.88% and 92.93%reaction conversion rate ofcomposites respectively.Energy spectrum analysis shows that the composite beads had silicon,which suggested polystyrene coated silica aerogel successfully.Pentane has infiltrated into composite bead by high pressure in a reaction kettle for foaming the beads.In order to reduce the test timesand at the same time identify the key factors in the test,an orthogonal experiment was a must including three factors about reaction temperature,pressure,pentane content and each factor with three levels.Deviation decomposition method shows that pentane content was most important,then the temperature,the last pressure.The optimized result was 100℃,1.1 MPa,10vol% pentane content.The result of the verification experiment agreed with the optimized result.Scanning electron microscopy show expandable beads had higher porosity and more crack than those of beads without pentane.The more nanoparticles in composites,the more pores and cracks.Steam foaming was utilizedto achieve the expandable composite bead.Scanning electron microscopy showed thatunder the same steam pressure prolonging foaming time could decreaseapparent density.Composite with 40 s steam time and 20vol% SiO₂ aerogel had22.5% apparent density.Under same foaming time introducing more particles could reduceits apparent density.Ultimately the best foaming processwas 0.5 MPa steam pressure and 40 s foaming time.With improving particles,cell density increased.As increasing SiO₂ aerogel,the bubble density increased from 3.12×107cell/cm3 to 4.59×109 cell/cm3,and the thermal conductivity coefficient decreased from 0.02699 W·m-1·K-1 to 0.02493W·m-1·K-1.With increasing NanoSiO₂,bubble density increased from 3.29×107cell/cm3 to 7.39×109cell/cm3,and the thermal conductivity coefficient decreased from 0.03308W·m-1·K-1to 0.02637 W·m-1·K-1.Introducting silica aerogel had better effect on decreasing thermal conductivity coefficient of polystyrene composite cystosepiment than that of introducing nano silica perhaps because of the special nano pore of silica aerogel and the interface between aerogel and ploystreyene.