ABSTRACT
The concern in environmental waste management and toxicity of petroleum derived plastics has led to the search for renewable, nontoxic and biodegradable materials for packaging. Starch is the most studied and promising biopolymer for the production of biodegradable films, but this starch films have poor properties which can be improved by blending with other materials and plasticizers. Borassus aethiopum shoot starch locally known as “Muruci” is a promising film forming biopolymer with high amylose content. Completely randomized design was used in this research with four factors; Borassus aethiopum shoot starch (BS), chitosan (CHI), glycerol (GLY) and shea butter (SB).This study presents the evaluation of the effect of plasticizer types (GLY) and (SB) singularly and in combination with varying concentration over the range of 0 to 50 % w/w on Borassus aethiopum shoots starch/Chitosan films (BSCF). Solution casting technique was employed for the film preparation at 800C. Starch from African Palmyra Palm (Borassus aethiopum) shoot has 20 % dry weight with amylose content of about 75.4 %. After series of different ratio combinations, the best films were formed from 2 %w/v of chitosan and starch composites in the presence of 30 %w/w GLY and 1 %w/w SB which were smooth and less transparent. Thickness, solubility in water, tensile strength (TS) and elongation at break (EAB) of BSCF were analyzed. Significant (p<0.05) increase in the films TS and thickness was observed with the increase in solute concentration of starch and CHI, while the Solubility in water and EAB decreases. Plasticizers incorporation significantly (p<0.05) increases the films thickness but lowered the film’s TS. Presence of GLY increased the films solubility and EAB significantly (p<0.05), but the introduction of SB significantly reduced the films thickness and solubility in water, singularly and in combination with GLY. Biodegradability test shows that the films with high chitosan concentration in the presence of SB had the longest degradation time (33 days). The transparency of BSCF is generally low and increase in the film opacity was observed with increase in solute concentrations of the starch. This study demonstrated that the BSCF in the presence of glycerol and low concentration of shear butter as plasticizers is a biodegradable film with the strength and barrier property needed for several applications such as in packaging.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
The desire to protect the environment has led to the research in developing environmental friendly materials. Since the discovery of crude oil, there have been high rate of production of petroleum products with desired properties for both domestic and industrial uses, but with negative consequences to the environment and human life. Petroleum products are non-renewable, difficult to recycle and are not biodegradable; therefore the need to develop environmental friendly materials becomes paramount. The already known chemistry of biomaterials has helped the growing demand for the development of a range of biodegradable polymers in the emerging technologies such as tissue engineering, regenerative medicine, novel drug delivery systems, nanotechnology and implantable devices (Heller et al., 2003).
Polymeric materials are either made from natural or synthetic polymers. Natural polymers are those from proteins, lipids and carbohydrate sources (Pascall et al., 2013), while the synthetic ones are those from petrochemical sources such as polyolefins, polyvinyl chloride, polyamides, polyvinylidene chloride, polystyrene, polyethylene and polyimides. Due to the drawbacks in synthetic polymers such as toxicity and non- biodegradability, the use of biopolymers which can be degraded by enzymes could be implored to ameliorate these limitations (Shanta et al., 2015). The world is driving towards the use of renewable natural materials with the sole aim of facing out toxic polymers in packaging. Polymers from carbohydrate source (polysaccharides) such as starch alginate, cellulose ethers, chitosan, carageenan, or pectins are renewable biopolymers which can be used for the manufacture of films with potential to improve food shelf life and quality (Sothornvit and Krochta, 2001). They can also impart hardness, adhesiveness compactness, thickening quality, viscosity, and gel forming ability to a variety of films.
Films in the area of biosciences refer to materials made from polymers with the thickness generally not more than 0.3 mm (Sentrurk et al., 2018). The thicker layers of polymeric materials are called sheets. Films made from renewable biopolymers have not yet found wide use in food packaging. Reasons behind this are that such biopolymers present problems when processed with traditional technologies as well as show inferior performances in terms of functional and structural properties (Mensitieri et al., 2011). However, base formulations are widely being studied to improve their performance and processing (Verbeek, 2011). Amongst natural polymers, starch is one of the most promising of all on the basis of biodegradability, availability, renewability, non-toxic and affordability (Dang & Yoksan, 2015).
Starch and its major components, amylose and amylopectin are biopolymers, which are attractive raw materials for use as barrier in packaging materials. Starch is primarily derived from cereal grains. It is the major carbohydrate reserve in plant tubers and seed endosperm where it is found as granules, each generally containing several million amylopectin molecules in composition with much larger number of smaller amylose molecules (Stephen et al., 2016). Amylose is responsible for the film forming properties of starch to replace plastic polymers either to used alone because of its low cost and renewability or in combination with other polysaccharides such as chitosan (Claudia, 2005). Starch often used in industrial foods. They have been used to produce biodegradable films to partially or entirely replace plastic polymers because of its low cost and renewability, and it has good mechanical properties (Xu et al., 2005).
However, wide application of starch film is limited by its mechanical properties and efficient barrier against low polarity compounds (Azeredo et al., 2000). In order to overcome its shortcoming, Bourtoom and Chinnan (2008) blend rice starch with different chitosan to increase the tensile strength. A major component of biodegradable films is the plasticizer, as well as the film-forming polymer. Addition of a plasticizer agent as well as other polymeric materials such as chitosan is required to overcome some of the drawbacks with starch films (Bourtoom, 2008).
Chitosan is the deacetylated derivative of chitin; it is a natural polycationic linear polysaccharide (Zvezdova, 2010). It is composed of β-(1-4) linked D-glucosamine and N-acetyl-D-glucosamine randomly distributed within the polymer (Chandy et al., 1990). The interesting characteristics of chitosan such as biocompatibility, low toxicity, low allergenicity and biodegradability allow it to be used in various applications (Kumar et al., 2004). The reaction of chitosan is more versatile compared to that of cellulose due to the presence of -NH2 groups (Dutta et al., 2004). Other naturally occurring polysaccharides such as cellulose, dextran, pectin, alginic acid are variably acidic or neutral, but chitosan is highly basic in nature. Due to this unique property, chitosan has several functional properties such as the ability to form films, chelate metal ion and optical structural characteristics (Kumar, 2010). Findings show that films produced from chitosan are brittle and not suitable for use in the dry state (Chang et al., 2019). These properties of chitosan films can be overcome by incorporating other polysaccharides and plasticizers.
Plasticizer is a substance or material incorporated into another material (usually a plastic or an elastomer) to increase its flexibility, workability, or distensibility as defined by International Union of Pure and Applied Chemistry (IUPAC). A plasticizer may reduce the viscosity, lower the temperature of a second-order transition, or lower the elastic modulus of the product (Sobral et al., 2001). Plasticizers like glycerol, sorbitol and mannitol are polyols commonly used in preparation of edible films from hydrophilic materials like those from starch source. But the choice of plasticizer depends on the compatibility between plasticizer and polymer for effective plasticization. Carefully plasticized African palmyra palm (Borassus aethiopum) shoots starch blended with chitosan can form a desired film.
African Palmyra palm (B. aethiopum) is a palm tree having huge fan shaped leaves (Balami et al., 2016). It is called Giginya in Hausa, Agbonoloduin Yoruba and Ubiri in Igbo (Umar et al., 2015). The shoot of B. aethiopum is a well-known source of dietary carbohydrate in some parts of Northern Nigeria. It is obtained by burying the matured seeds of the plant in a pit and allowing it to germinate. The young germinating shoot or hypocotyls locally known as “Muruchior Gazari”, is usually harvested after 7 to 8 weeks of planting (Ali et al., 2010). The study of plasticizer effect on the blend of chitosan and African palmyra palm (Borassus aethiopum) shoots starch will provide us with better understanding on how to control and improve the processing of films from this carbohydrate. It can further lead to commercialization of these polysaccharides based films for packaging.
1.2 Statement of the Research Problem
As the plastic industry continuously grows, there are concerns in the area of environmental pollution, renewability and toxicity from the use of synthetic polymers in packaging. These petroleum based polymers are nonrenewable, non-biodegradable and also not easily recycled. Phthalates are the most used plasticizers in production of these synthetic plastics which is toxic and have higher tendency to migrate into food (Sunny et al., 2004), thus, the need for eco-friendly materials and safe plasticizers.
The search for renewable and eco-friendly material had led to the discovery of starch polymers which has excellent film forming ability with good chance of replacing synthetic polymers, but starches from common sources (cassava, rice, yam, potatoes and corn) are scarce and expensive due to their high demand for food and industrial use, therefore the need for cheaper and underutilized starch sources (Zhu, 2020).
Films from starch polymers have poor properties such as high water sensitivity and low mechanical properties which are not suitable for many applications (Han et al., 2006, Shen et al., 2010, Kuorwel et al., 2013). Several researchers have experimented on the use of chitosan and plasticizers such as polyols (glycerol, sorbitol and manitol) and oils (peanut oil and soybean lecitin) to improve the low mechanical properties and high water solubility of starch films, but the high cost of some of these plasticizers (oils) due to high demand for consumption and other industrial uses is big hurdle to overcome, therefore the need for cheaper and under-utilized source of oils as plasticizers.
The use of this oil (shea butter) as plasticizer singularly and in combination with glycerol on starch films is yet to be established and the information on effects of shea butter and glycerol as plasticizers for the preparation of films from blends of chitosan and starch from Borassus aethiopum shoot composites is presently not readily available. Therefore, this investigation was designed to make a comparative study of the effects of glycerol and shear butter as plasticizers and their concentrations on films from blends of Borassus aethiopum shoot starch and chitosan, which could lead to low cost-effective films with excellent tensile strength and good water resistivity for commercial use.
1.3 Aim and Objectives
1.3.1 Aim
The aim of this study was to investigate the effects of different concentrations of glycerol and shea butter as plasticizers on the properties of films produced from blends of chitosan and Borassus aethiopum shoot starch composites.
1.3.2 Objectives
The specific objectives are to;
i. Determine starch yield of Borassus aethiopum shoot and amylose/amylopectin ratio.
ii. Determine the properties of films produced from blends of chitosan and Borassus aethiopum shoot starch composites.
iii. Determine the effect of glycerol and shear butter on the properties of films from blends of chitosan and Borassus aethiopum shoot starch composites.
iv. Optimize the production of glycerol and shear butter plasticized films from blends of chitosan and Borassus aethiopum shoot starch composites.
v. Determine the biodegradability of glycerol and shear butter plasticized films produced from blends of chitosan and Borassus aethiopum shoot starch composites.
1.4 Justification for the Study
Abundance, renewability and eco-friendliness are the major factors that have led to the increased interest in starch-based films. Starch from Borassus aethiopum shoot is easily processed and preliminary examination of this starch shows that it has high amylose content, which is the prerequisite for excellent film forming ability. Currently, the starch from Borassus aethiopum shoot is not being deployed for any known industrial uses, therefore making the starch affordable. The utilization of this starch would encourage its cultivation and subsequently improves farmer’s income.
The low mechanical properties of starch-based films led to the Introduction of chitosan which is compatible and provide necessary toughness and barrier properties to starch films. But the films from starch and chitosan blends are still brittle, therefore the need for plasticizers (glycerol and shea butter). Glycerol has often been used as a plasticizer since it is also compatible with amylose and as such, it improves the stiffness of starch films by decreasing intermolecular forces between amylose molecules. The introduction of glycerol to starch-based films is often accompanied with high film solubility which is a drawback and this drawback could be ameliorated by introducing oils such as shea butter. Shea butter is less expensive and presently used in cosmetic industries. Therefore its use as plasticizer in starch-based films could lead to increased cultivation of shea tree and oil production, which in turn could improve farmer’s income generation.
This study was designed to promote the use of cost effective materials in the production of active biodegradable films for commercialization.
This material content is developed to serve as a GUIDE for students to conduct academic research
EFFECT OF GLYCEROL AND SHEA BUTTER ON THE PROPERTIES OF FILMS PRODUCED FROM CHITOSAN AND Borassus aethiopum STARCH COMPOSITES
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