Effect of cellulose nanocrystals and gelatin in corn starch plasticized films

Published Date

doi:10.1016/j.carbpol.2014.08.057

Open Access, Elsevier user license

Author 

J.S. Alves ^a,,

K.C. dos Reis ^b,

E.G.T. Menezes ^a,

F.V. Pereira ^c,

J. Pereira ^a,

• aDepartamento de Ciência dos Alimentos, Universidade Federal de Lavras, Caixa Postal 3037, CEP 37200-000 Lavras, MG, Brazil
• bDepartamento de Ciências Exatas, Universidade Federal de Lavras, Caixa Postal 3037, CEP 37200-000 Lavras, MG, Brazil
• cInstituto de Ciência Exatas, Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, Pampulha, Caixa Postal 702, CEP 31270-901 Belo Horizonte, MG, Brazil

Received 22 April 2014. Revised 19 July 2014. Accepted 13 August 2014. Available online 3 September 2014.

Highlights

• •
  Cellulose nanocrystals were added in the corn starch/gelatin films.
• •
  Physical, mechanical and microstructural properties were investigated.
• •
  Higher concentrations of gelatin and CNC resulted in better mechanical properties.
• •
  The films were homogeneous indicating the interaction between filler and matrix.
• •
  Low content of gelatin and CNC increases the degradation temperature.

Abstract

Cellulose at the nanoparticle scale has been studied as a reinforcement for biodegradable matrices to improve film properties. The goal has been to investigate the properties of starch/gelatin/cellulose nanocrystals (CNC) films. Eleven treatments were considered using RCCD (rotatable central composite design), in addition to four control treatments. For each assay, the following dependent variables were measured: water vapor permeability (WVP), thickness, opacity and mechanical properties. The microstructure and thermal properties of the films were also assessed. Increases in gelatin and CNC concentrations lead to increases in film thickness, strength and elongation at break. The films containing only gelatin in their matrix displayed better results than the starch films, and the addition of CNC had a positive effect on the assessed response variables. The films exhibited homogeneous and cohesive structures, indicating strong interactions between the filler and matrix. Films with low levels of gelatin and CNC presented the maximum degradation temperature.

Chemical compounds studied in this article

• Glycerol (PubChem CID: 753)
• Sulfuric acid (PubChem CID: 1118)
• Water (PubChem CID: 962)

Abbreviations

• CNWs, cellulose nanowhiskers
• CNCs, cellulose nanocrystals

Keywords

• Biopolymers
• Nanobiocomposite
• Mechanical properties
• Packaging
• Barrier properties
• RCCD

---

1 Introduction

Starch is widely used in the form of biodegradable films in varied applications because it is a renewable, abundant and inexpensive material. According to (Fakhouri et al., 2007), films produced from polysaccharides or proteins have excellent mechanical, optical and sensory properties but are sensitive to humidity and have a high water-vapor permeability coefficient. Nevertheless, this problem can be mitigated by adding plasticizers (polyols, such as glycerol, sorbitol and polyethylene glycol) or reinforcements.

Another edible and renewable raw material used in the production of biodegradable films is gelatin. Gelatin is a protein of animal origin obtained from collagen through acid or alkaline hydrolysis that is widely used in both food and pharmaceutical industries. Gelatin preparation may or may not involve alkaline pretreatment, which converts asparagine and glutamine into their respective acids, resulting in greater viscosity. The acid pretreatment (type A gelatin) uses pig skin, whereas the alkaline pretreatment (type B gelatin) uses cattle hides and bones. All types of gelatin have similar composition, containing water, a small amount of minerals and pure connective tissue protein (Almeida & Santanta, 2010). Gelatin is primarily used as gelling agent to create transparent, elastic gels that are thermo-reversible under cooling below 35 °C (Teixeira, 2011). According to Bertan (2003), as cited by (Fakhoury et al., 2012), gelatin-based bioplastics are resistant, transparent and easy to handle.

One of the most promising technical advances in the material industry has been the development of nanobiocomposites, namely, the dispersion of nanosized filler reinforcements into a starch biopolymer matrix (Xie, Pollet, Hallet, & Averous, 2013). Cellulose is the most abundant organic compound on earth and is found in plant cell wall in association with hemicellulose and lignine. From cellulose, the natural nano-reinforcements, called cellulose nanowhiskers (CNWs) or cellulose nanocrystals (CNCs) can be obtained using a controlled sulfuric acid hydrolysis, producing highly crystalline rod-like nanostructures (Mesquita, Donnici, & Pereira, 2010).

CNCs (cellulose nanocrystals) act as reinforcement in biodegradable polymers, interacting with the matrix mainly to favor mechanical and barrier properties (Cao et al., 2008a, Cao et al., 2008b, Kaushik et al., 2010, Lu et al., 2006, Mathew et al., 2008and Svagan et al., 2009). This change allows a broader range of usage for these materials, especially in the packaging industry. In the present experiment, a film made from corn starch and glycerol and supplemented with gelatin was developed to obtain a more cohesive matrix. CNCs were also incorporated to this film to improve mechanical, thermal and barrier properties.

2 Materials and methods

2.1 Materials

Corn starch (Amidex^® 3001) was supplied by Corn Products Brazil S/A, glycerol was purchased from Vetec Quimica Fina Ltda. (São Paulo, Brazil) and bovine gelatin, of 180 Bloom and 30 mesh, was obtained from Gelita do Brazil Ltda. (São Paulo, Brazil).

2.2 CNC preparation

CNC was obtained according to Beck-Candanedo, Roman, and Gray (2005) with modifications according to Mesquita et al. (2010). Sulfuric acid hydrolysis of eucalyptus wood pulp was performed. Briefly, the wood pulp was ground until a fine particulate was obtained using a Willey mill. Then, 10.0 g of cellulose was added to 80.0 mL of 64 wt% sulfuric acid under strong mechanical stirring.

Hydrolysis was performed at 50 °C for approximately 50 min. After hydrolysis, the dispersion was diluted twice in water, and the suspensions were then washed using three repeated centrifuge cycles. The last washing was conducted using dialysis against deionized water until the dispersion reached pH 6.0. Afterward, the dispersions were ultrasonicated with a Cole Parmer Sonifier cell disruptor equipped with a microtip for 8 min and finally filtered using a 20 mm pore size filter.

2.3 Film preparation

The films were prepared using a casting process, which consisted of dehydrating a filmogenic solution applied on a support (Henrique, Cereda, & Sarmento, 2008). The filmogenic solutions were prepared from 3% corn starch, 20% glycerol and gelatin solution and cellulose nanocrystals (CNC) according to the experimental range as shown in Table 1.

Table 1. Experimental range and levels of independent variables.

Variables	Coded variables	Variables Levels
		− 1.41	− 1	0	+ 1	+ 1.41
Gelatin (g 100 g−1)	X1	6	7.16	10	12.84	14
CNCa (%)	X2	0	0.44	1.5	2.56	3

• a
  CNC = cellulose nanocrystals.

To improve the barrier properties of the films, in each of the 11 treatment trials (T1–T11) (Table 2), two suspensions were prepared, one with corn starch and the other with gelatin. Then these two solutions were combined. The gelatin solution was prepared by hydrating gelatin with distilled water for an hour, heating in a water bath until complete solubilization and then adding glycerol from solution. The solutions with CNC were prepared by addition of CNC to glycerol at ambient temperature, and there was occurrence of the birefringence phenomenon as observed through crossed polarizers. The solution (CNC and glycerol) was mixed with corn starch and distilled water under stirring and heating until 75.0 °C. The two suspensions, corn starch and gelatin, were mixed to create a single suspension. The mixture was cooled to room temperature and poured onto polystyrene plates, which were dried in a controlled temperature chamber at 25 °C at 50% RH in circulated air (chamber model 435314, Hotpack, Philadelphia, USA). The dried films were peeled off the casting surface and stored in polyethylene bags at 25 ± 1 °C until evaluation.

Table 2. Experimental design for corn starch/gelatin/CNC films treatment and observed data values of water vapor permeability (WVP), thickness measurements (TM), opacity (Op), puncture force (PF), tensile strength (TS) and elongation at break (EB).

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S0144861714008339