Elsevier

Polymer

Volume 45, Issue 19, 3 September 2004, Pages 6665-6673
Polymer

Rheological and mechanical properties of PVC/CaCO3 nanocomposites prepared by in situ polymerization

https://doi.org/10.1016/j.polymer.2004.07.045Get rights and content

Abstract

Poly(vinyl chloride) (PVC)/calcium carbonate (CaCO3) nanocomposites were synthesized by in situ polymerization of vinyl chloride (VC) in the presence of CaCO3 nanoparticles. Their thermal, rheological and mechanical properties were evaluated by dynamic mechanical analysis (DMA), thermogravimetry analysis (TGA), capillary rheometry, tensile and impact fracture tests. The results showed that CaCO3 nanoparticles were uniformly distributed in the PVC matrix during in situ polymerization of VC with 5.0 wt% or less nanoparticles. The glass transition and thermal decomposition temperatures of PVC phase in PVC/CaCO3 nanocomposites are shifted toward higher temperatures by the restriction of CaCO3 nanoparticles on the segmental and long-range chain mobility of the PVC phase. The nanocomposites showed shear thinning and power law behaviors. The ‘ball bearing’ effect of the spherical nanoparticles decreased the apparent viscosity of the PVC/CaCO3 nanocomposite melts, and the viscosity sensitivity on shear rate of the PVC/CaCO3 nanocomposite is higher than that of pristine PVC. Moreover, CaCO3 nanoparticles stiffen and toughen PVC simultaneously, and optimal properties were achieved at 5 wt% of CaCO3 nanoparticles in Young's modulus, tensile yield strength, elongation at break and Charpy notched impact energy. Detailed examinations of micro-failure micromechanisms of impact and tensile specimens showed that the CaCO3 nanoparticles acted as stress raisers leading to debonding/voiding and deformation of the matrix material around the nanoparticles. These mechanisms also lead to impact toughening of the nanocomposites.

Introduction

Poly(vinyl chloride) (PVC) is one of the major thermoplastics used today, and a large amount of PVC is produced worldwide [1]. However, processability and thermal stability of PVC are inferior to those of other commodity plastics, like polyethylene and polystyrene [2]. Much improvement of the inferior properties of PVC has been carried out by the incorporation of additives such as plastizers, heat stabilizers, lubricants, fillers and copolymerization with other monomers [1]. Amongst these methods, compounding PVC with inorganic fillers is a convenient and efficient method. It is well known that the mechanical properties of composites are strongly related to the filler aspect ratio. Hence, polymer/intercalated or exfoliated montmorillonite (MMT) nanocomposites have attracted considerable attention due to their high strength, superior modulus, good heat distortion temperature and enhanced barrier and flame retardant properties [3], [4], [5], [6], [7]. Recently, intercalated PVC/MMT nanocomposites were prepared by melting and solution compounding [8], [9], [10]. Later, exfoliated PVC/MMT nanocomposites were also synthesized by in situ intercalation polymerization of vinyl chloride (VC) and organic MMT [11], [12], [13]. However, their low fracture toughness has greatly limited their applications. The challenge is to find novel methods to enhance the fracture toughness [14]. In contrast, nanosized particles, like silica and calcium carbonate filled-polymer composites possess greatly improved rigidity and toughness if the ultra-fine phase dimensions of nanoparticles are retained after compounding with a given polymer matrix [14], [15], [16], [17], [18], [19], [20], [21], [22].

Nanoparticles have a strong tendency to agglomerate; hence, the homogeneous dispersion of nanoparticles in a polymer matrix is a major problem. The sol–gel process provides a method of preparation of inorganic metal oxides under rather mild conditions starting from organic metal alkoxides [23], [24], [25], [26], [27]. This permits structural variation without compositional alteration. In contrast, in situ polymerization is commonly used to prepare nanoparticle-filled composites with good dispersion, where the nanoparticles are first dispersed in the monomer; then, the mixture is polymerized using a technique similar to bulk polymerization [15], [28]. In this work, we have prepared the PVC/calcium carbonate (CaCO3) nanocomposites by in situ polymerization of vinyl chloride (VC) in the presence of nanosized CaCO3 particles, and their rheological and mechanical properties are studied.

Section snippets

Materials

Calcium carbonate nanoparticles with an average size of 44 nm were supplied by Chengdu Nano Technology Group, China. Vinyl chloride monomer (VC) was provided by Wuhan Gedian Chemical Group Co. Ltd, China. The thermal stabilizer (XP-301) was a mixture of plumb salts. The processing aid (ACR-401) was an acrylate resin. They were provided by Zibo Plastics Chemical Co., China. Paraffin wax and stearic acid were industrial grade products commercially available.

Synthesis of PVC/nanoCaCO3 compounded resins

The PVC/nanoCaCO3 compounded resins were

Micromorphological structure of PVC/CaCO3 nanocomposites

Fig. 1 is a TEM micrograph of PVC/CaCO3 nanocomposites with 5 and 7.5 wt% CaCO3. For the 5 wt% CaCO3 nanocomposite, a good dispersion is achieved. Most CaCO3 are uniformly distributed as nanosized particles in the PVC matrix. It is well known that nanoparticles can be easily dispersed in an adequate solvent under vigorous stirring. During the polymerization reaction, VC monomers may enter the gaps and empty space between the primary particles under a stirring environment. So, polymerization can

Conclusions

Poly(vinyl chloride) (PVC)/calcium carbonate (CaCO3) nanocomposites were synthesized by in situ polymerization of vinyl chloride (VC) in the presence of CaCO3 nanoparticles. The results showed that CaCO3 nanoparticles were uniformly distributed in the PVC matrix. The glass transition temperature (Tg) and 5% weight loss temperature (T5%) of PVC phases in the PVC/CaCO3 nanocomposites were slightly higher compared to pristine PVC due to the restriction of CaCO3 nanoparticles on the segmental and

Acknowledgements

The authors are grateful for the financial support of the Chinese National Natural Science Foundation (20490220 and 50003005) and the Australian Research Council (ARC). YWM wishes to acknowledge the award of an Australian Federation Fellowship by the ARC tenable at the University of Sydney. XLX is Visiting Scholar to the CAMT supported by the ARC.

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