Preparation Of High Melt Strength Polystyrene And Its Foaming Behavior Study

As the most common moisture-proof insulation and packaging cushioning material on the market currently, the consumption of polystyrene(PS) foams is increasing year by year. If we can use a simple method to further improve the foaming properties of PS foam and increase the expansion ratio of PS, we can further reduce the foam density and save the cost of production.This experiment selects the styrene (St) as polymerization monomer, isobutyronitrile (AIBN) as initiator, divinyl benzene (DVB) crosslinking agent, toluene as solvent to crosslinking modify the PS resin. In order to improve the foaming properties, we improved the melt strength of modified samples by an appropriate degree of cross-linking. The experimental data showed that the regulation of St monomer concentration is the most effective means to control the gel content. Set the dosage of initiator (AIBN) as 2% of the amount of monomer (St), the amount of crosslinking agent (DVB) 3% of the amount of both PS and St is more appropriate. Solvent toluene has very little effect on the gel content, the dosage should be just enough to make the liquid soak the solid particles.The reaction temperature is set as 65℃, swelling time is three hours. Comparison of foaming ratios of the modified samples with diverse gel contents at different foaming temperatures shows that under the temperature of 175℃, foaming ratio of modified sample whose monomer additive amount was 5 share, the gel content was 4.9% reached maximum, maximum ratio is about 10% larger than pure PS foam samples.Study on foaming properties shows that with the increase of gel content, the average pore size of the foamed samples becomes smaller and the pore size distribution becomes narrower and pore morphology becomes more regular. The melt strength test data showed that:with the increase of the gel content, the melt strength increases. Compared with the unmodified pure PS foam sample, the melt strength of the sample who has the highest expansion ratio increased by 43.7%. Analysis of rheological behavior of modified samples shows that in low frequency shear the modified sample’s storage modulus G’increased significantly, the complex viscosity was also significantly increased, loss factor tanδ decreased obviously, indicating the modified sample’s elasticity and viscosity increased, internal friction reduced.This modified method can be used in the application of wasted PS recycling. The modified sample experienced extrusion for only once had the largest foaming ratio which is a little greater than pure PS foam and the average pore size becomes smaller, the pore size distribution becomes narrower and pore morphology becomes more regular than unmodified waste PS foams.Melt strength test showed that the melt strength of modified samples are improved obviously. The melt strength of optimal sample is about 5% higher than pure PS. Under low frequency shear the modified waste polystyrene’s storage modulus G’and the complex viscosity was improved, the loss factor tanδ reduced. The rheological properties of the optimal sample is better than the pure PS samples.