Processing of PLA nanocomposites with cellulose nanocrystals extracted from Posidonia oceanica waste: Innovative reuse of coastal plant

https://doi.org/10.1016/j.indcrop.2015.01.075Get rights and content

Highlights

  • Cellulose nanocrystals (CNC) were isolated from Posidonia oceanica waste.

  • The surface of nanocrystals was also modified using a commercial surfactant (s-CNC).

  • Poly(lactic acid) (PLA) nanocomposites reinforced with CNC and s-CNC were developed.

  • The surfactant favours the CNC dispersion in the polymer supporting their effect on PLA properties.

  • PLA/cellulose systems can be used as new bio-nanocomposites in industrial applications.

Abstract

Poly(lactic acid) (PLA) nanocomposite films, reinforced with cellulose nanocrystals (CNC) extracted from Posidonia oceanica plant waste, were produced by solvent casting and their morphological, mechanical, thermal, optical and migration properties were studied. Cellulose nanocrystals were successfully extracted through an optimized chemical treatment, followed by sulphuric acid hydrolysis. The nanocrystals were added to the neat polymer at two different weight percentages (1 and 3%wt) using a commercial surfactant to increase the dispersion of CNC in the biodegradable matrix. All the nanocomposites kept the optical transparency of the PLA matrix, while morphological investigations underlined the rougher fracture surfaces of the CNC based systems and a more porous structure of the PLA matrix, induced by the addition of surfactant modified s-CNC. The surfactant favours the cellulose nanocrystal dispersion in the polymer matrix, remarkably enhancing the nucleation effect for matrix crystallization and producing its plasticization. The migration levels for all the studied nanocomposites were well below the legislative limits required for their use as food packaging materials. The successful production of biodegradable nanocomposites incorporating cellulosic sources from biomass waste suggests the possibility of using these new bio-nanocomposites in industrial applications.

Introduction

In the last few years, biodegradable polymers have been investigated and considered as an alternative to non-degradable matrices, in order to develop new environmental friendly materials able to address the problems generated by plastic waste. Poly(lactic acid) (PLA) is one of the most important organic candidates for food packaging (Averous, 2004); this polymer is a thermoplastic polyester derived from renewable resources, such as the fermentation of starch and other polysaccharides and represents a valid alternative to petrochemical-derived products (Fortunati et al., 2012). Bio-based polymers have a lower negative environmental impact than traditional plastics. Products realised when using a PLA matrix are biodegradable, compostable and may be dumped in ideal conditions since they completely disappear in less than one month (Jonoobi et al., 2010, Oksman et al., 2003). In last few years, PLA is becoming more and more popular due to its superior transparency, high mechanical properties and easy processability with respect to other green polymers (Arrieta et al., 2014a, Arrieta et al., 2014b). PLA is an economically feasible material (Auras et al., 2004) and one of the most interesting biomaterials approved by the US Food and Drug Administration (FDA) as a food contact substance; it is used as packaging for some short shelf-life applications (Arrieta et al., 2013, Hwang et al., 2012) and it is also used in rigid and flexible food packaging applications (Boonyawan et al., 2011). Furthermore, PLA is used to produce disposable cutlery (plates, salad cups, drinking cups, lids and drinking straws), film packaging and bags (Auras et al., 2005). However, when compared to equivalent petroleum based polymers used in food applications, PLA suffers the limitations of lower water permeability (necessary for fresh food packaging), poor oxygen barrier characteristics and relatively poor thermal and mechanical properties (Petersen et al., 2001). Therefore, the development of nanocomposites represents a valid method to increase the physical properties of biodegradable polymers, without affecting their transparency (Fortunati et al., 2012a). Among the many nanoparticles adopted as nano-reinforcements for bio-based polymers, cellulose nanocrystals are gaining more and more interest as they represent a feasible method for increasing the properties of a biomaterial suitable for food packaging (Šturcová et al., 2005). Cellulose nanocrystals (CNC) can be obtained in the form of rigid rod monocrystalline domains with diameters ranging from 1 to 100 nm and from 10 to 100 nm in length (Matos Ruiz et al., 2000). In general, the nanocrystal aspect ratio (diameter/length) can vary from 1:1 to 1:100 and the dimensions of the CNC depend on the raw material utilized for their extraction and the intensity of the chemical process for their production (Cranston and Gray, 2006, Fortunati et al., 2013a, Fortunati et al., 2013b). CNC have a crystalline structure (Fortunati et al., 2012b) and an elastic modulus ranging at around 150 GPa (Cavaille et al., 2000). However, cellulose nanocrystals are very difficult to use in a nanocomposite approach with water insoluble polymers like PLA, because their high ability to produce strong hydrogen bonding. Therefore, CNC have to be transferred from water to an appropriate solvent in order to produce and process composite systems. In this context, physical modification by commercial surfactant was found to be a possible strategy to obtain a better dispersion of CNC in an organic solvent and, consequently, in the used polymer matrix (Petersson et al., 2007).

Posidonia oceanica is a Mediterranean alga that appears as raw material with balls shape (Aegagropili) in many beaches. Some studies have focused on the potential use of the fibrous wastes of P. oceanica, for example, they have been used as a source of fillers for potato starch-based films with interesting results (Khiari et al., 2011). Moreover, fibres from P. oceanica were hot-pressed with wheat gluten protein as a binder-matrix material to obtain polymer composites based on fully renewable resources (Ferrero et al., 2013). The use of these fibres as a reinforcement in a polyethylene/maleic anhydride grafted polyethylene matrix was also reported (Puglia et al., 2014). Other research has focused on the possibility of extracting high-grade cellulose (97% α-cellulose) from P. oceanica using H2O2 and organic peracids, (Coletti et al., 2013) or on the production of carboxymethyl cellulose from bleached cellulose pulp (Aguir and M’Henni, 2006). Few examples are reported in literature regarding the extraction and characterization of cellulose crystallites from algae or marine plant (Hanley et al., 1997, Hua et al., 2014, Revol, 1982, Saritha et al., 2013) while Bettaieb et al. (2014) reported about the preparation and characterization of cellulose nanostructures (both nanocrystals and nanofibrils) from P. oceanica.

Based on this background, the extraction of CNC from P. oceanica by acid hydrolysis was performed and their novel integration in a biodegradable PLA matrix for the production of bio-nanocomposites has been proposed in this work.

P. oceanica is characterized by relatively high amounts of ethanol/toluene extractives (10.7%), ashes (12%) and 40% of cellulose content. Moreover, lignin content is relative high (Khiari et al., 2010). Therefore, the extraction of high crystalline cellulose represents a relevant challenge for P. oceanica waste. As a result, the research reported in this paper focuses on the optimization of the extraction of CNC from P. oceanica and their use for the development of fully compostable and biodegradable PLA matrix films for food packaging applications. The final goal of the research was to assess the production of a polymer film with good mechanical properties whilst at the same time maintaining the optical transparency and thermal stability of the neat polymer. In order to increase the dispersion of cellulose nanocrystals in the PLA matrix, the surface of the nanocrystals was modified using a commercial surfactant, according to previous results obtained by Fortunati et al. (2012). Thereafter, the morphological, thermal, mechanical and migration properties of the PLA based nanocomposites containing surfactant modified s-CNC was compared with the results obtained with the unmodified CNC based PLA formulations.

Section snippets

Materials

Poly(lactic acid) (PLA) in the form of fibres (specific gravity of 1.25 g cm−3) was supplied by MiniFibres, Inc. (USA). P. oceanica waste raw material was collected by Aitex (Alcoy, Alicante, Spain). All the chemical reagents were supplied by Sigma–Aldrich® and used as received.

Fibre chemical pre-treatment

P. oceanica raw material (Fig. 1a) was washed and rinsed several times in distilled water in order to eliminate sand and other soil contaminants, after which, it was dried in an oven at 80 °C for 24 h. Then they were chopped

Characterization of bleached fibres and cellulose nanocrystals from P. oceanica

The dimension and microstructure of unbleached and bleached fibres were investigated by visual observation and FESEM investigation, while the morphological features of cellulose nanocrystals (CNC) extracted by means of the hydrolysis procedure were analysed with AFM. The results are summarized in Fig. 1, Fig. 2. Fig. 1a,c give an indication of the appearance of the unbleached and bleached fibres. The mean diameter of the unbleached fibres obtained from the raw material was 84 ± 26 μm (Fig. 1b).

Conclusions

Poly(lactic acid) (PLA) based nanocomposite films reinforced with cellulose nanocrystals (CNC) and functionalized cellulose (s-CNC), proposed for industrial application for food packaging, were successfully developed and characterized.

Acicular cellulose nanocrystals (CNC) with dimensions ranging around 180 nm in length and 5 nm in diameter on average were isolated by acid hydrolysis from P. oceanica plant wastes with a 14% yield and were added to the neat PLA polymer at two different weight

Acknowledgements

The authors acknowledge the financial support of the SEAMATTER European project: Revalorisation of coastal algae wastes in textile nonwoven industry with applications in building noise isolation, LIFE11 ENV/E/000600, Funding Program: LIFE+. Call 2011. We also wish to acknowledge the “Materials + Technologies” Group from the University of the Basque Country UPV/EHU, Spain and in particular Prof. Aitor Arbelaiz for atomic force microscopy investigations.

References (48)

  • E. Fortunati et al.

    Binary PVA bio-nanocomposites containing cellulose nanocrystals extracted from different natural sources: part I

    Carbohydr. Polym.

    (2013)
  • E. Fortunati et al.

    Nano-biocomposite films with modified cellulose nanocrystals and synthesized silver nanoparticles

    Carbohydr. Polym.

    (2014)
  • M. Jonoobi et al.

    Mechanical properties of cellulose nanofiber (CNF) reinforced polylactic acid (PLA) prepared by twin screw extrusion

    Compos. Sci. Technol.

    (2010)
  • R. Khiari et al.

    New lignocellulosic fibres-reinforced composite materials: a stepforward in the valorisation of the Posidonia oceanica balls

    Compos. Sci. Technol.

    (2011)
  • R. Khiari et al.

    Chemical composition and pulping of date palm rachis and Posidonia oceanica – a comparison with other wood and non-wood fibre sources

    Bioresour. Technol.

    (2010)
  • K. Oksman et al.

    Natural fibres as reinforcement in polylactic acid (PLA) composites

    Compos. Sci. Technol.

    (2003)
  • L. Petersson et al.

    Structure and thermal properties of poly(lactic acid)/cellulose whiskers nanocomposite materials

    Compos. Sci. Technol.

    (2007)
  • J.F. Revol

    On the cross-sectional shape of cellulose crystallites in Valonia ventricosa

    Carbohydr. Polym.

    (1982)
  • N. Wang et al.

    Thermal degradation behaviours of spherical cellulose nanocrystals with sulfate groups

    Polymer

    (2007)
  • C. Aguir et al.

    Experimental study on carboxymethylation of cellulose extracted from Posidonia oceanica

    J. Appl. Polym. Sci.

    (2006)
  • R. Auras et al.

    An overview of polylactides as packaging materials

    Macromol. Biosci.

    (2004)
  • R.A. Auras et al.

    Evaluation of oriented poly(lactide) polymers vs. existing PET and oriented PS for fresh food service containers

    Packag. Technol. Sci.

    (2005)
  • L. Averous

    Biodegradable multiphase systems based on plasticized starch: a review

    J. Macromol. Sci. Polym. Rev.

    (2004)
  • F. Bettaieb et al.

    Preparation and characterization of new cellulose nanocrystals from marine biomass Posidonia oceanica

    Carbohydr. Polym.

    (2014)
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