جستجوی مقالات مرتبط با کلیدواژه « biodegradable » در نشریات گروه « مکانیک »

Expanded Styrene is an inexpensive, readily available polymer used in packaging foams. With this, foams created on polystyrene cause environmental problems because they are non-degradable and have little recycling. Therefore, foams with energy sources are necessary for degradable production packaging and to deal with plastic issues. This review emphasizes different strategies of starch-based manufacturing, modification of starch-based foams to improve mechanical  properties and durability concerning humidity, biodegradable foams based on cellulose in anno to improve mechanical and thermal properties and related challenges in the development of bioplastic aimed at using them as alternatives to polystyrene in packaging. Starch source, process conditions, type of fiber and addition of other polymers, compatibility between composite components affect foam porosity, mechanical properties and morphology. In addition, these materials have positive environmental benefits and are desirable to be recycled. If these materials are to be increasingly sustainable and the challenges in their production and application due to the reduction of the effects of auxiliary plastic materials, performance characteristics such as durability, strength and low price can be considered for the use of these products. Therefore, study and investigation in the field of foams based on degradable biological materials with suitable properties.

Eggs are an inexpensive food with various nutrients and high biological value. The decline in egg quality starts immediately after laying and progresses rapidly depending on the storage conditions. To aim of preventing the penetration of microorganisms and gas and mass exchanges, various approaches were studied based on inactivating microorganisms and coating the pores on the eggshell, in order to maintain the quality and extension of the egg shelf life. As an alternative to the traditional packaging of eggs and other food products, using biodegradable wrappers based on agricultural and food industries waste was associated with successful results. Polysaccharide packaging materials are low-cost and available, but they are not considered suitable wrappers against the penetration of water vapor, so this problem can be solved by applying physical and chemical modification methods and creating composite and active wrappers. Using food wrappers in the form of biodegradable packaging, in addition to preventing food wastage and longer protecting food, is an effective approach to overcoming the problems of waste disposal. At the same time, proper design and appearance, economic justification, using devices and practical methods in preparation, and appropriate, compatible, efficient and competitive formulation should also be considered.

Ordinary plastics have been produced and used for many years for packaging applications in various sectors. With the growth of the food industry, the demand for food packaging has also grown. However, the plastics made from petroleum are non-degradable, which has created severe bio environmental problems for the environment. Biodegradable polymers are an alternative approach to many industrial applications including food packaging, as well as risk control for non-biodegradable plastics. According to the type of the raw material, they are classified in one of the following categories: polymers extracted from biomass compounds, polymers synthesized from monomers and polymers produced from microorganisms. The quality of biopolymers depends on their physical, mechanical and thermal properties. The present study is an overview of the properties of different biopolymers and their compounds, comparing the properties of biodegradable polymers and biopolymers. The recent research works and innovative methods for the use of these plastics for food packaging and biomass plastic poisoning have also been studied and presented, concluding that biodegradable polymers help reduce the environmental impacts of plastics. It is worth mentioning that as the plastics from agricultural waste are used as raw materials for making this kind of packaging, there is a great opportunity to increase added value.

In this study, the compression behavior of cardboard egg box cores with various stacking sequences used in sandwich structures is investigated both experimentally and numerically. A critical requirement of the design is that the structure is compatible with the environment (biodegradable), and its properties have been investigated through compression and tension testing. Egg boxes were chosen as the core material for sandwich structures due to their mechanical properties, excellent insulation properties, and strength. Also, the core shape in various stacking sequences were modeled in ABAQUS Finite Element code to simulate the behavior of the egg box core in compression. The results showed that the surrounding edges of the core were crushed and the truncated top region compressed. The increase in thickness of the egg boxes directly affected the compression properties. By doubling the thickness of the layers, the amount of energy absorbed by the core increased by more than 100%. By comparison of various stacking sequences of the cores, the one with double layers of the egg boxes overlapped showed an increase of 49% in stiffness, 108% in energy absorption, and 128% in strength. According to the results, the tangled arrangement of the second type of the core exhibits the highest load bearing, the greatest energy absorption, and less damage as compared to other core stacking sequences.

The importance of environmental issues has increased the use of biodegradable polymers which nowadays have become among main components in medical and biological applications. In the present study, a new combined method of fused filament fabrication (FFF) and batch foaming was introduced to improve the properties of poly lactic acid. For this purpose, FFF samples were produced with infill percentages of 100, 80 and 60 and then, foamed in batch process. Due to the importance and effect of the void fraction on structural and mechanical performance as well as the biodegradability of materials with porous structure, especially for medical purposes, void fraction and impact strength were evaluated. The results showed that the void fractions of FFF samples were 3%, 13% and 25% in infill percentages of 100, 80 and 60, respectively while after the foaming they reached to 14%, 19% and 30%. The findings revealed that the impact strength of FFF foamed samples was improved compared to FFF solid samples. For samples with 100 infill percentage, the impact strength improved from 207 to 506 J/m2 due to the foaming procedure with nano-sized cells created by the batch foaming.

In this study, the mechanical properties of poly lactic acid samples produced by FDM 3D printing technique were investigated. The 3D printing process parameters were optimized using design of experiment (DOE) Taguchi approach for achieving the optimum mechanical performance. In this regard, infill percentage (at three levels of 30, 50, and 70%), raster angle (at three states of 0/90, -30/30, and -45/45 degree), and layer thickness (at three levels of 200, 250, and 300 µm) were considered as process parameters for optimization procedure. Their effects on density (as porosity degree), impact strength (as mechanical property), and specific impact strength (the impact strength to density ratio) were investigated. Analysis of variance (ANOVA) was utilized to find the most effective processing parameters. The findings revealed that the infill percentage was the most effective parameter on the density and the impact strength. The density and the impact strength were reduced with the decrease of the infill percentage. These decrements were in a way that their ratio, specific impact strength, was almost constant. The layer thickness had the most influence on the specific impact strength. The specific impact strength was improved by reducing the layer thickness due to the raster entanglement. The optimum conditions to achieve the highest mechanical performance were the raster angle of 30/-30 degree and the layer thickness of 200 µ. The optimum infill percentage depended on the application.

Foam packaging involves long-term storage and protection of a variety of foods against physical, chemical and biological agents. Polymer foams are safe and recommended for many applications due to their very light weight, high versatility, durability, mold resistance and good appearance. This has led to high production and consumption of these materials, and due to the non-biodegradability of these materials, they have caused a lot of environmental concerns. Therefore, significant efforts have been made to develop environmentally friendly alternatives, especially in the case of starch foams. Because starch is a cheap, available, abundant, renewable and biodegradable biopolymer. These properties make starch the most important biopolymer for the development of biodegradable films, but the starch itself is relatively weak and water-sensitive. To improve the thermal and mechanical properties, moldability, water impermeability and other properties of starch-based foams, many approaches such as chemical modification of starch, combination with various biodegradable polymers, combination with natural fibers and the addition of nano-fillers are proposed.

In this study, biodegradable starch-based films were made as biodegradable packaging by solution molding method. The effect of addition of titanium dioxide nanoparticles (at three levels of 1, 3 and 5 wt. %) on the films prepared from starch biopolymer was evaluated. Surface properties, physical properties, water vapor permeability, mechanical properties and microstructure characteristics of the samples were investigated. The results showed that the addition of titanium dioxide nanoparticles reduced the water-dependent properties (water vapor permeability, solubility and water absorption) of the starch film. Titanium dioxide nanoparticles reduce the tensile strength and increase the elongation of the films. Scanning electron microscope observations showed that most of the physical properties of the films were related to their microstructure.

The use of edible films and coatings derived from natural biopolymers in the food industry has gained great deals of attraction due to environmental reasons.These films and food coatings, by reducing the exchange of moisture and gases between the environment and food, can reduce the oil absorption during frying and improve the quality and durability of the food. In the present research, an edible, biodegradable film containing carboxymethyl cellulose (CMC) and guar gum containing zinc oxide nanoparticles was synthesized through casting method and the effect of the presence of zinc oxide nanoparticles on the coated product was investigated to investigate the physical and mechanical properties of the films. CMC and guar gum were mixed at different ratios, namely 0:100, 30:70, 50:50, 70:30, and 100:0. In the synthesis of the coatings, glycerol was used as a plasticizer. The effect of each of these percentages on mechanical properties, roughness, gas transmissibility, moisture content, the amount of oil absorption andantibacterial characteristics were studied. The mechanical properties test showed that, by adding the nanoparticles, the elongation percentage, increase of modulus value and tensile strength decreased. In atomic force microscopy (AFM) images captured from the film containing zinc oxide nanoparticles, roughness and bumps were observed to increase, and the accumulation of nanoparticles in the biopolymer film has increased. The results of the study of the antimicrobial characteristics of the edible film indicate that the absence of the nanoparticles in the edible coating positively contributes to bacterial growth. Considering the disadvantages of high oil content in fried products and the effect of edible coating on reducing oil absorption, results of applying the edible coating on potato and eggplant showed that there is a direct correlation between oil absorption and moisture loss in potatoes and eggplants. There is a marked decrease in oil absorption during frying.The highest moisture content and the lowest amount of oil absorption were observed in the sample coated with 70% CMC and 30% guar. Furthermore, trying to apply the coating on strawberry, the film containing CMC and guar at 70:30 ratio had the best durability up to day 5. As a result, the coating developed a suitable barrier to passage of gases and moisture.

Today, an important part of the materials used in the food packaging industry is oil derivatives. This has caused much environmental pollution in the world. One of the proposed solutions to tackle this problem is the use of edible and biodegradable films as a good alternative to nondegradable polymers. Starch is being studied for its ability to form film, availability, renewability and low cost as a bio-polymer, but disadvantages such as high hydrophilic properties and poor mechanical properties limit the industrial use of this highly valued material. The presence of hydroxyl groups in the starch chains creates a hydrogen bond between the polysaccharide and water. Also, there is a lot of free space in the starch chains, so that molecules of water can easily pass through this space. Today, many researches has been done to reduce hydrophilic properties of starch using genetically modification, enzymatic, chemical (esterification, acetylation, phosphorylation) the use of nanoparticles in the polymer matrix, starch composition with lipids, and other biopolymers. Most of the methods are based on inhibition of starch hydroxyl groups in various ways. One of the methods for inhibiting the starch hydrophilic groups is the esterification of starch chains with hydrophobic agents, the formation of emulsions by fatty acids, and the filling of pores in the polysaccharide network by nanoparticles.

In recent years, Mg alloys have received much attention as a promising candidate for raw material in biodegradable vascular stent. Forming of Mg alloys is difficult because of poor workability of them at room temperature. Hence this presents a technological barrier to the fabrication of initial micro-tube for a biodegradable stent. With regard to high biodegradability of the magnesium alloy WE43 to manufacture biodegradable stent, it has been selected as initial with casted structure. In this study, for enhancing mechanical properties and attaining micro tube a combination of equal channel angular pressing (ECAP) with extrusion and micro extrusion was used and Mg bars were fabricated to high-quality micro-tubes with refined microstructure. Fine-grained size billets of the WE43 alloy were obtained by one-pass of ECAP. The processed Mg bar was extruded into a bar with 5 mm in diameter. Finally, a UFG and high strength micro tubes with an outside diameter of 3.4mm and a wall thickness of 0.25mm were successfully produced by micro extrusion process. Mentioned processes were simulated using finite element (FE) simulations. The result shows the grain size of Mg incredibly reduced after this combined method and mechanical properties were significantly improved.

Protein based films used for food packaging despite having numerous benefits like biodegradability and renewability suffer from essential drawbacks of weak mechanical and water vapour barrier properties. In recent years efforts for improving functional properties of such films from various resources, through modifying formulation, molecular crosslinking and promote proteins based composite films have been increased. In this paper some early researches on improving functional properties of protein films obtained from different resources via preparing composite protein films have been reviewed.

It seems that today whole world seems to be wrapped in plastics. Almost every product we buy, most of the food we eat and many of the liquids we drink, come encased in plastics. The environmental impact of persistent plastic wastes is evoking more global concern as alternative disposal methods are limited. Incineration may generate toxic air pollution, and satisfactory landfill sites are limited. Also, the petroleum resources are finite and are becoming limited. Global working on biopolymers was initiated from 1970 in the petroleum crisis time. Those days, developed countries were interested in using special materials for packing purposes which were free from petroleum and its derivatives, so biopolymers has been tested. Starch is an inexpensive hydrocarbon and can be found abundantly in plants. It possess weak polymer properties and can be attained the properties of petroleum polymers by modification. The shape of starch-based utensil is the same as plastic utensil except for being biodegradable. In recent years, there has been a marked increase in interest in biodegradable materials for use in packaging, agriculture, medicine, and other areas.