Optimizing the Production of Thermoplastic Starch using Cellulose Filler

Background: Plastic contamination, especially in packaging application, has been the main issue for universities and industry. Bio-composite of biodegradable Starch is considered as an appropriate replacement for starch due to low price, availability and biodegradability.
The film or coating is placed on the food as an integrated and thin layer of different polymer compounds. Today, contaminants from synthetic polymers have drawn attention to the use of biodegradable materials, and over the past two decades, the study of biodegradable materials derived from proteins and carbohydrates has expanded. These macromolecules could potentially be a viable alternative to synthetic polymers derived from petroleum products.
Goal: In the present study, different starch films have been produced by corn starch and natural cellulose booster from 0% to 20% applying melt mixing with twin extruder. The aim of this study is to obtain a suitable combination of starch with cellulose (natural and degradable) that makes starch similar to synthetic polymers with low water permeability and high mechanical strength and can be a good alternative for them. In addition, food additives such as citric acid and stearic acid are used in a constant amount to facilitate the process and improve the properties of the film
Methodology: The current study aims at investigating the effect of cellulose, as an intensifier, and different ratio of glycerol/sorbitol, as an emollient, on the improvement of starch bio-composite. The optimum point for starch bio-composite is obtained by Design Expert Software and structural tests, TGA and XRD, were conducted on this point.
For this study, corn starch was purchased from Qazvin Glucose Company, microcrystalline cellulose (Avisel) from Chengdu (China) and glycerol, citric acid and stearic acid from Merck (Germany). Other materials used were prepared using laboratory grade. First, a suspension of cellulose and a certain amount of water were homogenized or subjected to ultrasound so that the starch could be well dispersed in the matrix. Raw material for the production of starch biocomposites, including corn starch (as a matrix), glycerol and sorbitol (as a softener and each from 10 to 20% by weight of starch), different amounts of cellulose fiber (from 0 to 20% by weight of starch), citric acid 1% by weight To improve the biocomposite, starch and stearic acid were physically mixed as a process aid (to prevent starch from adhering to equipment and 1% by weight of starch) (Landavi et al. 2015). The main mixing was done uniformly in the two-screw face extruder. The produced starch biocomposite or sheet was exposed to 50% relative humidity and 30°C for one week and then the necessary tests were performed on them. In the next step, the mold was used under pressure, until a starch sheet with a thickness of 1 mm was produced. The sheets were produced at a temperature of 160°C and a pressure of 25 MPa for 2 minutes. The temperature reached 50-40°C by the flow of cold water flowing around the mold and the pressure was removed. Then each sheet was qualified separately at 58% RH and 30°C and entered the test stage. The thickness of the film was measured randomly in 5 positions with the micrometer of incision (model W-3275-A, USA) with a resolution of 0.01 mm and their average was used for calculations.
In order to investigate the mechanical properties of nanocomposite films, mechanical properties including tensile stress, elongation at break (strain) and Young's modulus were calculated. Mechanical properties were determined at each rupture. Fracture stress and strain (σ, ε) were calculated for each sample. The film strips were cut to a length of 100 mm and a width of 20 mm and adjusted for 48 hours at a temperature of 23°C and a relative humidity of 53%. Tissue analysis performed by TA.XT plus histometer device made by Stable Microsystem of England and with Texture Expose 32 software was used to measure the mechanical properties of the film. Separation initial velocity and shear rate were 50 and 30 mm/ min, respectively. The elongation and tensile strength at the point of rupture were calculated from the deformation and the force of the data recorded by the software. 8 replicates of each sample were evaluated
Findings: optimum point was 5% cellulose and 17.5% of each emollient which has Water Vapor Permeability (WVP) as 7.81*10-10 gs-1m-1Pa-1, tensile strength of 0.85 MPa, Young module 277.56 MPa and elongation at break point 7.08%. The optimum glass transition temperature of bio-composite starch increases to 130o C. Although optimum bio-composite XRD show high picks demonstrating crystals, the findings from thermal weighting reveal that optimum bio-composite will be decomposed about 300. According to decomposition of natural starch at 220oC, this thermal resistance can be ascribed to the cellulose in its structure.
Final Findings: It is concluded that the composition of microcrystal cellulose and equal glycerol/sorbitol ratio lead to the development of starch bio-composite properties.
The aim of this study was to obtain a suitable combination of starch with cellulose (natural and degradable) and glycerol and sorbitol softeners that make starch similar to synthetic polymers with low water permeability and high mechanical strength. Be a good substitute for them. In this study, optimization of starch biocomposite formulation was performed by epithelial mixing method. The main purpose of optimization was to place the parameters of tensile strength, elongation and elastic modulus in the desired range and to minimize water vapor permeability. According to the modeling, the optimal treatment in the production of starch biocomposite was 5% cellulose, 17.5% glycerol and 17.5% sorbitol. The validation results of the answers showed that the results of the model have an acceptable similarity with the practical results. X-ray diffraction test to investigate the distribution of particles in the polymer matrix showed that the components of the composites are well dispersed. Behavioral patterns related to heat-weight changes of starch biocomposite showed that three main stages of degradation and weight loss were observed in starch biocomposites. The results of this study can open a new window towards the use of biodegradable packaging in the food industry to improve food quality and safety and reduce food waste. More research is needed to replace conventional plastics with green composites to at least protect human health and the environment.