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Foam Biodegradable Foams

Foam Biodegradable Foams Containing Recycled Cellulose Article contributed by M. Avella M. Cocca M. E. Errico G. Gentile Istituto di Chimica e Tecnologia dei Polimeri Pozzuoli (Na), Italy Figure 1. PVOH based foams. Polymer foams are found virtually everywhere and are used in a wide variety of applications such as thermal and acoustic insulation, energy dissipation, shock protection, packaging, etc. due to their specific properties [1]. The growing use of foams, particularly in the packaging sector, is causing serious problems concerning their disposal. In this respect numerous attempts have been focused on the development of biodegradable materials. Interest in environmentally friendly materials has stimulated development of foams from biodegradable and renewable resources, such as polyvinyl alcohol (PVOH), poly ε- caprolactone (PCL), polylactic acid (PLA) and starch, to replace expanded polystyrene (EPS) [2]. With this aim, composites based on eco-friendly polymers filled with natural fibres are emerging materials, attracting the attention of many industrial sectors [3]. Natural fibres are widely used as reinforcements in thermoplastic and thermosetting polymers due to their wide availability, low cost and high specific properties [4]. Moreover, it is worth mentioning the positive environmental benefit gained by the use of such materials [5]. Furthermore, in recent years the recycling of cellulose-based materials has attracted great interest because it represents one of the most promising waste disposal strategies [6]. In this paper, results of tests on foams consisting of biodegradable polymers and recycled cellulose-based materials, derived from industrial scrap, are briefly presented. In particular, two families of materials were developed. In the first, recycled multilayer cartons (MC), produced from cellulose and low density polyethylene (80/20 wt/wt), were used as a direct source of cellulose reinforcement in PVOH based foams. These foams (Fig. 1) were produced by an innovative and eco-friendly methodology based on a modified overrun process. This process was able to generate a pore structure, without the need for chemical agents or chemical reactions, by entrapping air into the polymer/filler aqueous dispersion during the high speed mixing. The resulting foams were characterized by a dual-pore structure consisting of large pores due to the air entrapped into the polymer matrix and small pores due to the water removal during freezedrying, as can be seen in the SEM micrographs of foam 34 bioplastics MAGAZINE [01/11] Vol. 6

Foam PVOH PVOH-MC 70-30 PVOH-MC 60-40 PVOH-MC 40-60 samples (Fig. 2). Swelling tests revealed a progressive decrease in the swelling ratio with the increase of MC content. This behaviour was ascribed to interactions occurring between PVOH and MC phases which involve the formation of hydrogen bonds between the free hydroxyl groups of PVOH and those on cellulose chains. Improvements of the compression properties and thermal stability were recorded in all PVOH/MC foams. These findings can be also considered as a result of a good interaction between filler and polymer. Figure 2 Scanning electron micrographs of PVOH based foams In the second system chestnut shell (CS) was used as cellulose reinforcement in Starch/PCL foams. Starch/ PCL (80/20 wt/wt) based foams were prepared by a baking process which involves heating of starch, water, and additives into a mould. During heating the water vaporizes, acting as a foaming agent. Pictures of the resulting foams are shown in Fig. 3. The starch/PCL based foams were characterized by a thin surface ‘skin’ of approximately 150 µm in thickness, and an internal region characterized by a cellular structure with large pores up to 1 mm in size. Morphological analysis (Fig. 4) revealed that the cellular structure was almost preserved up to 20 wt% content of chestnut shell. Chestnut shell was able to decrease the rate of water absorption of starch/PCL foams while its possible reinforcement effect is still under investigation. References [1] S.Cotugno, E. Di Maio, G. Mensitieri, L. Nicolais, S. Iannace, Biodegradable foams - Handbook of Biodegradable Polymeric Materials and Their Applications, American Scientific Publishers, (2006). [2] P. D. Tatarka, R. L: Cunningham, J Appl Polym Sci 67 (1998), 1157. [3] R. M. Rowell, A. R. Sanadi, D. F. Caulfield, R. E. Jacobson, Utilization of natural fibers in plastic composites: problems and opportunities - Lignocelluloisc-plastic composites. Leao AL, Carvalho FX, Frollini E, editors, (1997). [4] M. Avella, L. Casale, R. Dell’Erba, B. Focher, E. Martuscelli, A Marzetti, J Appl Polym Sci 68(7), (1997) 1077. [5] A. K. Mohanty, M. Misra And G. Hinrichsen, Macromol. Mater. Eng. 276/277 (2000), 1. [6] C. A. Ambrose, R. Hooper, A. K. Potter, M. M. Singh, Resour Conserv Recycling 36 (2002) 309. Figure 3 Starch/PCL based foams Starch/PCL Starch/PCL-CS 95-5 Starch/PCL-CS 90-10 Starch/PCL-CS 80-20 Figure 4 Scanning electron micrographs of Starch/PCL based foams. bioplastics MAGAZINE [01/11] Vol. 6 35

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