Microstructure and mechanical properties of poly (vinyl chloride) modified by silica fume / acrylic core-shell impact modifier blends

Abstract

This research explored replacing acrylic core-shell impact modifier (AIM) by silica fume to toughen PVC. 100%, 75%, 50% and 25% of AIM (8 phr) were substituted by silica fume in PVC respectively, and then processed by dry blending and twin-screw extrusion. Severe silica fume agglomeration was observed by scanning electron microscope (SEM) in the PVC matrix when 8 phr pure silica fume was used and processed by screw speed of 20 rpm. Its tensile strength was thereby reduced by 38% comparing to unmodified PVC. The silica fume was successfully dispersed while the screw speed was slowed down to 10 rpm to give a stronger screw torque and a longer melt residential time in the extruder. The tensile strength was ‘recovered’ to a level comparable to unmodified PVC. Impact test were performed on all formulations extruded at 10 rpm screw speed and synergetic toughening effect was found with 50% substitution and it had the impact strength that was comparable to 8 phr pure AIM toughened PVC.

Keywords

silica fume / acrylic impact modifier / synergetic effect / poly (vinyl chloride) / tensile strength / impact modification / twin screw extrusion

References

[1] Malhotra V. M., Ramachandran V. S., Feldman R. F. Condensed Silica Fume in Concrete[M], 1987 Florida CRC Press

[2] Siddique R. Utilization of Silica Fume in Concrete: Review of Hardened Properties[J]. Resour. Conserv. Recycl., 2011, 55: 923-932.

[3] Sezer G. I. Compressive Strength and Sulfate Resistance of Limestone and/or Silica Fume Mortars[J]. Constr. Build. Mater., 2012, 26(1): 613-618.

[4] Yajun J., Cahyadi J. H. Effects of Densified Silica Fume on Microstructure and Compressive Strength of Blended Cement Pastes[J]. Cem. Concr. Res., 2003, 33(10): 1 543-1 548.

[5] Zhang O., Zhang C., Wu L. Antiplasticizing Effect of MOCA on Poly(vinyl chloride)[J]. J. Wuhan Univ. of Technol.-Mat. Sci. Ed., 2011, 26(1): 83-87.

[6] Liu Y., Zhang C. The Influence of Additives on Crystallization of Polyvinyl Chloride[J]. J. Wuhan Univ. of Technol.-Mat. Sci. Ed., 2007, 22(2): 271-275.

[7] Kemal I., Whittle A., Burford R. Toughening of Unmodified Polyvinylchloride Through the Addition of Nanoparticulate Calcium Carbonate[J]. Polymer, 2009, 50(16): 4 066-4 079.

[8] Dompas D., Groeninckx G. Cavitation versus Debonding During Deformation of Rubber-modified Poly(vinyl chloride) [J]. Polymer, 1995, 36(2): 437-441.

[9] Gilbert M., Hitt D. J., Schmaucks G. Inorganic Impact Modifier and Processing Aid for PVC[J]. Plast. Rubber Compos., 2005, 34(3): 111-116.

[10] ASTM. Standard Test Method for Tensile Properties of Thin Plastic Sheeting[S]. ASTM D638, USA, 2003

[11] ISO. Plastics. Determination of Charpy Impact Strength[S]. ISO 179-1, Swizerland, 2010

[12] Zhao C. Z., Wu G. F., Zhou C. Independence of the Brittle-ductile Transition from the Rubber Particle Size for Impact-modified Poly(vinyl chloride)[J]. J. Polym. Sci. Pt. B-Poly. Phys., 2005, 44(4): 696-702.

[13] Du P., Yu J., Lin P. F. Effect of Rubber and Inorganic Rigid Particles on Fracture Behaviour of Injection-molded PVC Nanocomposites[J]. Acta Polym. Sin., 2011, 12: 1 395-1 401.