Elsevier

Waste Management

Volume 33, Issue 3, March 2013, Pages 598-604
Waste Management

Review
Recent progress on preparation and properties of nanocomposites from recycled polymers: A review

https://doi.org/10.1016/j.wasman.2012.07.031Get rights and content

Abstract

Currently, the growing consumption of polymer products creates the large quantities of waste materials resulting in public concern in the environment and people life. Nanotechnology is assumed the important technology in the current century. Recently, many researchers have tried to develop this new science for polymer recycling. In this article, the application of different nanofillers in the recycled polymers such as PET, PP, HDPE, PVC, etc. and the attributed composites and blends is studied. The morphological, mechanical, rheological and thermal properties of prepared nanocomposites as well as the future challenges are extensively discussed. The present article determines the current status of nanotechnology in the polymer recycling which guide the future studies in this attractive field.

Highlights

► The article determines the current status of nanotechnology in polymer recycling. ► The addition of nanofillers to waste polymers, composites and blends is discussed. ► The future challenges in polymer recycling using nanoparticles are explained.

Introduction

Polymers are the most widely used materials in various fields due to their valuable properties such as good mechanical properties, low density, rather low cost, and also ease of processing (Ansari and Alikhani, 2009, Rahimi and Shokrolahi, 2001). The total production of plastics is more than 230 million tonnes per year which will reach to 400 million tonnes in 2020 based on a more conservatively annual growth rate of about 5% (Braun, 2004, Simoneit et al., 2005).

Every year, large quantities of waste polymers are produced from industrial, agricultural and household activities. It has been reported that plastics make up more than 12% of municipal solid waste stream, a dramatic growth from 1960, when plastics were only 1% of the waste stream (http://www.epa.gov/osw/conserve/materials/plastics.htm). The new environmental, economic, and petroleum considerations have induced the scientific communities to increasingly deal with polymer recycling (Fall et al., 2010, Salmiaton and Garforth, 2007, Salmiaton and Garforth, 2011, Taurino et al., 2010).

The efficient treatment of waste polymers is still a difficult challenge. The traditional methods such as combustion or burying underground show a negative effect on the environment like formation of dust, fumes and toxic gases in the air, and the pollution of underground water and other resources. The recycling process is the best way to manage the waste polymers. There are various techniques for recycling of waste polymers including primary recycling, mechanical recycling, chemical or feedstock recycling and energy recovery (García et al., 2009, Sadat-Shojai and Bakhshandeh, 2010, Zhang et al., 2009b). The recycling rate for different types of plastic significantly varies, leading to an overall recycling rate of only 8% or 2.4 million tons in 2010 (http://www.epa.gov/osw/conserve/materials-/plastics.htm).

However, there are some main problems for polymer recycling such as separation (Burat et al., 2009). For example, PVC bottles are difficultly identified from PET ones, but one stray PVC bottle in a melt of 10,000 PET bottles can ruin the whole batch. For ease of separation, most manufacturers determine the type of plastics by the numerical coding system created by Society of Plastics Industry in 1980s (http://www.epa.gov/osw/conserve/materials/-plastics.htm). The identification codes can be found at the bottom of most plastic packaging. Table 1 shows the identification codes and some household applications of commonly used polymers. However, plastic tarps, pipes, toys, household coverage, and a multitude of other products do not fit into the numbering system. So, there are not usually collected as well as the thousands of different polymers. Moreover, after several processing cycles, the structure of polymer is degraded introducing the poorer mechanical properties than those of a virgin one (Goto et al., 2006, Oromiehie and Mamizadeh, 2004). To overcome these limitations, it seems that the easiest way to recycle the waste plastics is development of blends and composites.

Nanotechnology is assumed as one of the key technologies in the recent century (Shabani et al., 2012, Shabani et al., 2011a, Shabani et al., 2011b, Shabani et al., 2009). We can obtain the substantial enhancements of mechanical, thermal, optical and barrier properties using the nanofillers (Frounchi et al., 2006, Shahabadi and Garmabi, 0000, Zare and Garmabi, 2012a, Zare et al., 2011). The nano-additives increase the interphase surface of components and superficial area/volume ratio leading to improvement of overall performances. In comparison to traditional micro-fillers, very low loading of nanoclay is sufficient to achieve the excellent development of properties without substantially increasing the density and cost or reducing the light transmission properties of base polymer (Jafari et al., 2012, Ramezani-Dakhel and Garmabi, 2010, Zare and Garmabi, 2012b).

Further, the reduced melt strength of recycled polymers in extrusion process causes the inconsistency of material after leaving the die which makes the production of sheets or profiles impossible (Hamzehlou and Katbab, 2007, Kráčalík et al., 2007b). Also, reprocessing of waste PET with very small intrinsic viscosity is not feasible (Kráčalík et al., 2007c). Nanofillers can increase the melt strength and viscosity of recycled polymers in addition to improvement of various properties. The recent studies on polymer recycling by nanofillers are presented in Table 2.

In this review paper, a comprehensive study on the application of nanofillers in the recycling process of polymers, composites and blends is carried out. Moreover, the future challenges in this area are discussed which can help the researchers in the potential works.

Section snippets

Nanoclay content

Hamzehlou et al. have found the optimal nanoclay (DK2) content of 3 wt.% for tensile strength of both recycled and virgin PET nanocomposites (Hamzehlou and Katbab, 2007). However, it was clearly observed that all samples prepared from rPET showed the higher tensile properties, compared to virgin PET (vPET). Also, the onset of thermal degradation has been delayed for rPET nanocomposites composed of 3 and 5 wt.% of nanoclay. It exhibited the enhanced melt elastic modulus and pseudo solid-like

Conclusion and future trends

The current study shows that the application of much low content of nanofillers can be an efficient technique for recycling of polymers, composites and blends. Various nanoparticles such as nanoclay, CaCO3, CNTs, SiO2, mica and graphene have been used for recycling which should be developed for all waste polymers. Also, it is indicated that the application of a compatibilizer for recycling of polymers, particularly blends and composites are more useful.

However, with the objective to a

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