Research On In-situ Polymerization Of PMMA/phosphogypsum Composite Microspheres And Their Application

Phosphogypsum(PG)is a solid waste residue in the wet process of phosphoric acid,and a large number of deposits pollute the environment.However,after treatment and surface modification design,PG can be used as filler of polymer materials to toughen and strengthen,and improve the comprehensive performance of composite materials.Silane coupling agent,titanate,stearic acid(calcium)as small molecular modifier,organic chain is short,resulting in phosphogypsum and polymer matrix van der Waals effect is small,and small molecular coupling agent will migrate from the composite interface to the surface,resulting in the improvement of mechanical properties is not high.However,long-chain polymers penetrate deeper in polymer matrix.Therefore,in this paper,long-chain polymethyl methacrylate(PMMA)grafted coated modified phosphogypsum was designed to prepare composite microspheres and used for polypropylene(PP)blending to prepare composites.The effects of surface structure and state of modified phosphogypsum on the comprehensive mechanical properties of PP composites were investigated.Details and results are as follows:(1)Anhydrous phosphogypsum(APG)was prepared by PG pretreatment.The surface of APG was hydroxylated by Na OH solution.The surface hydrophobic modification of APG was carried out by γ-methacryloyloxypropyltrimethoxysilane(KH570),new alkoxytri(dioctyl pyrophosphate acyloxy)titanate(TCA-L38)and stearic acid(SA),respectively.The surface modification effect,surface chemical structure and state of modified APG(M-APG)were characterized and analyzed,and the functional mechanism of surface hydroxylation and modification of APG was clarified.The optimal experimental conditions obtained by response surface optimization were as follows: Na OH concentration of 2.6 mol/L,KH570 dosage of 3.1g,and reaction time of 150 min.After hydroxylation,APG significantly increased the surface hydroxyl content,thereby significantly increasing the grafting rates of KH570,TCA-L38 and SA on APG surface,which were 3.21 wt%,4.25 wt% and 9.91 wt%,respectively.The water contact angles of APG-OH-KH570,APG-OH-SA and APGOH-TCA were 80.52°,124.99° and 123.77°,respectively,which significantly increased the hydrophobicity of APG.The siloxane group of KH570,the carboxylic group of SA,the monoalkyloxy group of TCA-L38 and the pyrophosphate ester group reacted with the hydroxyl groups on the surface of APG,respectively,and they were tightly adsorbed on the surface of APG through chemical adsorption.(2)PMMA grafted M-APG composite microspheres were successfully prepared by in-situ suspension polymerization.Under the conditions of 200 g water,40 g MMA,4 g APG-OH-KH570,70 ℃ reaction temperature,0.8 g PVA,7 h reaction time,and 0.6g LPO,the grafting rate of PMMA/APG-OH-KH570 composite microspheres reached23.04 wt%,and the particle size of the composite microspheres was between 100 μm and 150 μm.The microspheres were regular and smooth.The water contact angle of PMMA/APG-OH-KH570 composite microspheres was 106.74°.The water contact angle of PMMA/APG-OH-KH570 composite microspheres with acetone extraction was 94.29°,which was significantly higher than 80.52° of APG-OH-KH570.PMMA/APG-OH-SA showed regular spherical shape.The average diameter of composite microspheres was about 100-160 μm,and the water contact angle was105.65°.PMMA/APG-OH-TCA showed irregular granular shape,rough surface,and the water contact angle was 104.87°.(3)M-APG and composite microspheres were used as PP fillers to prepare PP composites by melt blending.The effects of surface structure of APG modified by KH570,SA,TCA-L38 and long chain PMMA on mechanical properties of PP composites were investigated.The flexural strength,tensile strength and impact strength of APG-OH-KH570/PP,APG-OH-TCA/PP and APG-OH-SA/PP composites are better than those of pure PP.When 7.5% PMMA/APG-OH-KH570 composite microspheres were added,a large number of cracks existed in the cross section of PP composite.The presence of composite microspheres made the crack deflection of the composite at fracture.The tensile,bending and impact properties of PP composite were significantly improved,which were 18.52%,4.50% and 25.43% higher than those of pure PP,respectively.Compared with small molecular modifiers,PMMA long-chain coated APG is more conducive to improving the mechanical properties of PP/APG composites.