Elsevier

European Polymer Journal

Volume 42, Issue 8, August 2006, Pages 1811-1818
European Polymer Journal

The influence of arrangement of St in MBS on the properties of PVC/MBS blends

https://doi.org/10.1016/j.eurpolymj.2006.03.017Get rights and content

Abstract

Three series of MBS core–shell impact modifiers were prepared by grafting styrene and methyl methacrylate onto PB or SBR seed latex in emulsion polymerization. All the MBS modifiers were designed to have the same total chemical composition, and MMA/Bd/St equals 30/42/28, which is a prerequisite for producing transparent blends with PVC. Under this composition, there were three different ways of arrangement for styrene in MBS, which led to the different structure of MBS modifier. The concentration of MBS in PVC/MBS blends was kept at a constant value of 20 wt.%. The effects of arrangement of St in MBS on the mechanical and optical properties of PVC/MBS blends were studied. The notched Izod impact test results showed that the MBS with a PB homopolymer core grafted with St had a lowest brittle–ductile transition (BDT) temperature and BDT temperature increased with the amount of St copolymerized with Bd in the core of MBS. The transparency of blends also increased with the amount of St copolymerized with Bd in the core. TEM results showed that the arrangement of St in MBS influenced the deformation behavior. Two deformation modes were observed in the blends: cavitation and shear yielding. When all St was grafted onto the PB rubber, both cavitation and debonding were observed, which relieve the triaxial tension and promote the shear yielding of the PVC matrix. When all St was copolymerized with Bd in MBS, no cavitation could be observed and only the shear yielding of the PVC matrix took place.

Introduction

Mechanical properties of polymeric materials are decisive in applications. Improvement of toughness is of particular interest, since the toughness of material is an important selection criterion for many applications. Substantial enhancement of the toughness of brittle or notch sensitive polymers can be achieved by dispersing rubber particles in the polymer matrix. At the most basic level, rubber particles act as stress concentrators, which accelerate shear yielding in the matrix under a wide range of loading conditions [1]. In pseudoductile thermoplastic matrices, which deform preferentially by shear yielding, the major toughening mechanisms are thought to be cavitation of rubbery particles and shear yielding of matrix [2], [3]. Rubber cavitation occurs first, and this relieves the hydrostatic tension in the material and thereby promotes ductile matrix shear yielding.

Core–shell modifiers were commercially introduced as PVC impact modifies in 1958 [4]. The particle size of the core–shell modifier, which is set during the synthesis process, can remain after they are dispersed in a host matrix. The shell of modifier functions as the layer that physically binds the matrix to the rubber core. Core–shell modifiers are widely used in variety of polymers, such as PC [5], PMMA [6], PBT [7] and PVC [8]. Modern polymerization methods have led to the possibility of preparing core–shell modifiers with a range of different particle size and internal morphologies: they may contain several alternating layers of rubber and glassy polymer, the properties of the rubber itself can be altered, for instance, by crosslinking. The changing of the internal structure of the modifier may affect the subsequent deformation mechanism of its host matrix.

MBS is a typical core–shell rubber modifier, in which styrene and methyl methacrylate is graft polymerized onto polybutadiene (PB) or styrene–butadiene rubber (SBR) particles. The addition of MBS can improve the impact resistance of PVC without sacrifice its transparency. Much effort has been made to investigate the characteristic of MBS on the toughness of PVC. Takaki et al. [9] have studied the effect of rubber particle size on the fracture behavior of PVC/MBS blends. They pointed out that MBS with particle size of 200 nm could obtain maximum impact strength. They also studied the crosslinking degree of MBS on the impact strength of blends [10]. When the crosslinking degree of rubber was reduced, cavitations were liable to be formed in rubber during an impact test, and the Izod impact strength of PVC/MBS blend was improved.

This paper aims at studying the relation between the internal structure of the impact modifier and the mechanical and optical properties of PVC/MBS blends. Different internal structures of MBS with the same chemical composition are used, keeping the particle size constant (about 200 nm) and the MBS content in the blend constant (20%) and taking into account the effect of arrangement of St in MBS. The samples studied here cover three type of arrangement of St in MBS.

Section snippets

Materials

The MBS modifier consists of an elastomeric core and a glass shell. The elastomeric core is polybutadiene (PB) or styrene–butadiene rubber (SBR), and the shell is poly (methyl methacrylate) and polystyrene. The MBS copolymers were achieved by emulsion polymerization method. In the preparation process PB polymer and SBR have to be synthesized first and then St and MMA were polymerized on rubber particles. And the characteristics of the PB and SBR used in this paper were shown in Table 1. An

Characteristic of MBS

In order to investigate the influence of arrangement of St in MBS on the properties of blends, five MBS samples were synthesized. PS is a glassy polymer, so the difference of arrangement of St in core must lead to a different property of core in MBS. And the rubber would lose elastic when more St copolymerized with Bd in the core of MBS.

It is well known that MBS gives two tan δ peaks: one, in the low temperature, belongs to the rubber phase; the other, in the region of about 100 °C, belongs to

Conclusion

The influence of the arrangement of St in MBS on the properties of PVC/MBS blends was investigated in this study. The results of DMTA analysis illustrated that the arrangement of St in core of MBS had significant effect on the glass transition temperature of rubber phase. The results of Izod impact tests showed that the brittle–ductile transition temperature of blends shifted to higher temperature with the increase of the amount of St copolymerized with Bd in the core of MBS. The results of

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