جستجوی مقالات مرتبط با کلیدواژه « زیست تخریب پذیری » در نشریات گروه « فنی و مهندسی »

Cellulose is the main constituent of most plants. The renewability of this material has made it a natural raw material which is abundantly available and there is no need to worry about running out of its resources. However, the industrial application of cellulose as a thermoplastic polymer is associated with some problems and difficulties. Due to the presence of strong hydrogen bonds between its chains, cellulose is destroyed before melting. In order to eliminate such difficulties, researchers have developed celluloses derivatives. Ethyl cellulose is one of the most widely used polymers derived from cellulose. Today, cellulose derivative polymers, such as ethyl cellulose in particular, are widely used in numerous industries like ceramic manufacturing, cosmetics, pharmaceuticals, tobacco, paint, paper, food, textile, various molding parts and printing ink. Renewability, biocompatibility, and in some cases the biodegradability of this polymer along with its high tensile strength and appropriate toughness, make this polymer play a prominent role in polymer science and technology in the future. In this article, along with the introduction of ethyl cellulose, its various properties and characteristics, the different applications of this polymer's mixtures have also been reviewed.

Polyurethanes, mainly synthesized by addition reactions of polyols with diisocyanates, have been considered as the most widely used polymers in various industries due to the variety of raw materials, synthetic methods and properties. The high demand, the significant share of the world market and the abundant use of this category of polymers have involved the major consumption of petroleum-based polyols and diisocyanates. Nonetheless, environmental challenges and the crude oil crisis have led to greater interest in renewable resources and systems based on green chemistry. Today, with the synthesis of waterborne polyurethanes) WPUs) and the use of water as a safe solvent, the release of volatile organic compounds and the production of solvent-based systems have been prevented to a considerable extent. The non-toxicity, non-flammability, environmentally friendly, and the wide applications of WPUs in plastics, paints, adhesives, printing ink and biomaterials are among the reasons for further development of these water-based systems. Because there are only a few commercially available diisocyanates in the synthesis of WPUs, it is the choice of polyol which may determine the WPUs properties. The most convenient renewable raw materials are natural oils, polysaccharides, wood and proteins, and vegetable oils which are the most beneficial options and have been widely studied. Today bio-polyols obtained from different vegetable oils have become vital in the synthesis of WPUs. However, castor oil has attracted special attention, as an excellent substitute for petroleum-based polyols and has been used in polyurethane compounds due to its availability, biodegradability and inherent hydroxyl groups. Considering the importance of bio-polyols and their role in the development of vegetable oil-based WPUs, in this article, while briefly introducing WPUs and their synthetic methods, the properties of WPUs based on castor oil, as the only natural polyol, are reviewed. Some green approaches to acquire a clear picture of the current and potential future applications of WPUs based bio-polyols in various fields are introduced.

One of the most important problems of using magnesium alloys is their high corrosion rate. In order to solve this problem, the method of surface modification and coating has been considered. The main purpose of this research is to apply polycaprolactone/chitosan-1% Baghdadite polymer membrane by immersion method on anodized magnesium-aluminum AZ91 alloy in order to improve the corrosion resistance, biodegradability and biocompatibility of this alloy. The results of the electrochemical test show the improvement of the electrochemical resistance and the reduction of the electrochemical current density (10^3 times reduction) of the anodized magnesium-aluminum alloy AZ91 due to the application of the polymer-ceramic membrane. Also, the application of polymer-ceramic membrane has led to an increase in the surface roughness from 0.329 ± 0.02 (magnesium-aluminum AZ91) to 7.792 ± 0.34 micrometers. In order to evaluate the ability of apatite formation on the samples, the body simulating liquid test (phosphate buffer) was used. The results show that the formation of apatite layer on the surface of the sample can be considered as a measure of biodegradability

Every year, an enormous amount of 2.5 million tons of plastic enter the oceans. On land, plastic also accumulates in landfills, beaches and other sensitive ecosystems around the world which has been a huge concern through the years. Recent research has been conducted to show us that one type of worm may help us solve the huge problem of plastic waste. Scientists have discovered that the larvae of a type of worm, Mealworm called Tenebrio Molitor, can include styrofoam and other polystyrenes as well as polyethylene in their diet. Not only do worms go on a styrofoam diet, they say, but the microorganisms in their gut can break down plastics during their digestive process, turning it into carbon dioxide and eventually use it as the nutrients that their bodies need. Biodegradable materials disposed by worms also seem to be used as fertilizer to fertilize and impregnate agricultural soil. We are looking for solutions to implement this discovery in a way that eliminates plastic waste therefore can be a solution to clearer oceans, rivers and the entire environment from the inevitable consequences of plastic accumulation. In this review study, narrations from articles related to the biodegradation of polyethylene, polystyrene and polypropylene have been reviewed.

The feld of drug delivery is a very hot research area as it afects the life of millions of patients every year. Although pharmaceutical agents can be adminisrated in diferent ways, the efectiveness of certain drug delivery sysem (DDS) is directly related to the method of their adminisration. Polyurethanes are one of the mos important classes of polymers, that play an essential role in the development of many diferent biomedical devices due to their exceptional compatibility, mechanical properties and fexibility. Polyurethanes are formed by the reaction reviewed of isocyanates and diols to produce urethane-bonded polymers (-NH-COO-) in their main chain, which is similar to the peptide bonds in the sructure of proteins. Because of this similarity, they have also been used as part of the human body, such as dialysis membranes, intra-aortic balloons, heart valves, temporary scafolds and breas implants. There are many types of polyurethane sructural blocks available that allow the chemical and physical properties of polyurethane to be tailored to their intended applications, especially in the medical and pharmaceutical felds. In this paper, the synthesis and properties of polyurethane, sructure, thermal sability, hardness, solvent resisance, drug delivery, mechanical properties as well as biodegradability and biocompatibility with special emphasis on the application of the polymer in controlled release of drugs and delivery to the target tissue were.

Conventional plastics has a large impact in increasing the environment’s pollution. That’s why the interest has turned towards novel partially and completely biodegradable polymers. In this work, composites of polystyrene and starch with glycerol as plasticizer and compatibilizer were prepared in different ratios of starch and glycerol by melt mixing in twin screw extruder. To study the biodegradation properties, samples were buried in soil for 12 weeks and their weight changes were measured during two-week periods. Besides, the structure of prepared composites was studied using SEM analysis. To evaluate the impact strength and thermal properties of composites, we used Izod impact strength test, MFI (Melt Flow Index) and Vicat softening temperature tests. To examine the interaction between composite elements, thermal stability and degradation process, the samples were subjected to analysis using TGA. Biodegradation results and SEM analysis showed that the rate of biodegradation not only starch present in composites but also depends on the quality of starch particles dispersion. Notched Izod test showed the independence of samples impact strength to starch present. Due to the reduction of stress accumulation points, homogeneous dispersion of starch in the matrix leads to increase impact strength in unnotched Izod test. MFI test showed that addition of starch and glycerol leads to respectively increase and decrease in composites’ viscosity. Study of starch/glycerol ratio in obtained results showed that in an optimal amount of plasticizer, interaction between the composite components is in conditions that the best mode of starch particles dispersion is achieved in polystyrene matrix.

Research subject:

 The need to increase agricultural production in proportion to population growth and water crisis management requires initiatives that can increase the quantity and quality of crops by using soil moisture storage methods while preserving the environment. In this study, the effect of different wt. % of Thermoplastic starch (TPS) with maleic anhydride (MA) as compatibilizer and nanoclay (15A) on gel content and mechanical properties of Polylactic acid (PLA) and blends of  Linear low-density polyethylene/ Low-density polyethylene (LLDPE / LDPE) was evaluated.

Research approach: 

Here, 0, 10, 20 and 30 wt. % TPS were added to the blends of LLDPE/LDPE (20/80) and also PLA. Independent parameters in the experimental design were wt. % of TPS, basic polymer type that was PLA or TPS and aging test. For dependent parameters were considered gel content, tensile strength, elongation at break and elastic modulus. Experiments were designed in General Full Factorial Design and performed in three replications.

Gel content in LLDPE/LDPE blends increased with the addition of TPS and decreased for PLA blends. The gel content change range for experimental samples before and after the aging test was between 10 to 21 and 2 to 5 percent, respectively. Tensile strength and elongation at break were reduced by adding TPS in both series of compounds before aging test. But this reducing rate was less in the 20 wt. % of TPS. The values ​​of tensile strength and elongation at break were: 12 to 19 MPa and 50 to 350 percent, respectively. These values changed after the aging test between 7 and 11 MPa and from zero to 5 percent, respectively.
Keywords: biodegradability, low density polyethylene, poly lactic acid, thermoplastic starch.

Consumers now have stronger affinity towards eco-friendly products instead of plastics. Eco-friendly packaging is made of recyclable or renewable materials which are sustainable and safe for not only individuals but also the environment. Mushroom- based packaging is one of the eco-friendly materials that have received considerable attention, recently. Mycelium is a fast growing vegetative part of a fungus which latches onto whatever around it like any low value organic matter to create a super-dense network of threads. Once growing in the mold to reach the desired density and shape, the material is dehydrated and heat treated, to stop further growth. Supplementary processes such as compression and laser cutting may also be used to achieve the required shape and structure. The result is a heat and fire-resistant, biodegradable and low cost material that has similar properties like synthetic foam plastics. There is no spore or allergen concern as the mycelium is not fully grown to produce fertile bodies. This paper reviews the current status of technology for production of mycelium based material and its applications as a sustainable alternative for polystyrene.

Biodegradable packaging is a good alternative to synthetic film in the packaging industry because of its environmental-friendly. In this study, zinc oxide nanoparticles and thyme oil were used to enhance the structural properties of chitosan, which were produced for the purpose of chitosan - zinc oxide (0.01- 0.03%)  - thyme essential oil (0.25- 0.5%) nanocomposite. The differences between the synthesized samples with control film (blank) are for production of antibacterial and biodegradable packaging, the structural properties were investigated by infrared spectroscopy and X-ray diffraction, also the morphology of the synthesized particles was investigated by scanning electron microscopy. The results of the structural properties showed that the zinc oxide synthesized in the chitosan polymer matrix were nanoparticles. Based on the results, the water solubility and water vapor permeability of films decreased by 70% with increasing zinc oxide concentration and thyme essential oil. The interaction between chitosan, zinc oxide nanoparticles and thyme essential oil was confirmed by infrared spectroscopy and X-ray diffraction pattern. The findings of this study are an important factor for expanding the use of biodegradation films by improving their functional properties by nanoparticles.

Hydrogel is a three dimensional water insoluble polymeric network that can absorb body fluids in a biological environment. Its polymer network structure can be formed by chemical cross-linking such as photo-polymerization, enzyme-catalyzed reactions, and physical cross-linking induced by temperature, pH, and ionic interaction. Physical hydrogel is formed by weak secondary interaction. Covalent bonds are normally formed among polymer chains in a chemically crosslinked hydrogel. To synthesize hydrogels, natural and synthetic polymers were applied. Swelling, mechanical and biological properties of the hydrogels are the most important parameters that can be affected on its structure and morphology. The large volume of water that they can absorb and an ability to mimic the extracellular matrix environment are the main reasons for use the hydrogels for many biomedical applications such as tissue engineering, contact lenses, wound healing, and the controlled delivery of therapeutic agents. This review covers the various mechanisms of hydrogel formation, types of hydrogels, their properties and applications in the medicine.

The raising of global warming and environmental pollution has increased the use of biodegradable polymers. On of the most important polymers in this kind are poly (lactic acid) (PLA), which has can be produced by the melting process which is the most efficient method for the fiber production. Poly (lactic acid) is a biodegradable alternative to poly (ethylene terephethalate) (PET) , in many technical textiles and clothing products. Although PLA is similar to PET in various aspects, PLA has different dyeing conditions from it. The results of researches show that PLA absorption isotherm with natural and synthetic dyes follow from nernst and langmuir isotherms. This paper reviews the recent developments in the dyeing of PLA fibers and textiles with disperse, vat, cationic and natural dyes.

Hypothesis: Biodegradable polymer blends in comparison to petroleum-based polymers consume less energy in the production process, and do not produce environmental pollution due to their renewable sources. One of these biodegradable blends is polyolefin elastomer/starch (POE/S) blend. In this study, the effect of composition ratio of polyolefin elastomer/starch on properties such as mechanical, morphology, rheology and biodegradability properties of the blend were investigated. Because of non-polar microstructures of POE and polar starch, a polyolefin elastomer/maleic anhydride copolymer (POE-g-MAH) was used to improve their compatibility.
Blends of polyolefin elastomer and starch were prepared in presence of POE-g-MAH as synthetic compatibilizer with a Brabender internal mixer. The concentration of POE-g-MAH was fixed at 10 wt% and the content of starch in both binary and ternary blends was varied between 0 wt% and 55 wt%.
Findings: The results showed changes in the tensile, hardness, SEM micrographs, and void increasing after exposing the blends to fungi for three months at room temperature. To examine the compatibility of the blends, Fourier transform infrared spectroscopy (FTIR) was used. The observations of the scanning electron micrographs of polymer blends showed that by increasing the amount of starch from 15 to 55 wt%, the size of the dispersion phase increased; though it was reduced by adding 10 wt% of POE-g-MAH in the polymer blends. The rheology tests were carried out using rheometrics mechanical spectrometry (RMS) and the results indicated an increase in the complex viscosity, loss modulus and storage modulus after the addition of the compatibilizer into the blend. By adding starch to POE in the blend, the tensile strength and elongation-at-break decreased. The comparison between the blends with and without compatibilizer showed higher tensile strength and elongation-at-break for the blends with compatibilizer. The biodegradation experiments for the blend with 15 wt% of starch showed that the degradation of blend composition was negligible, but with higher starch content, the degradation rate increased and the blend with compatibilizer showed less degradation than the blend without compatibilizer.

The fabrication and characterization of bone scaffold which was produced from hydroxyapatite and polyurethane foam were investigated. Thermal and mechanical properties of the scaffolds were studied via X-ray diffraction, scanning electron microscopy, and compression test and thermogravimetry technique. Also, hardness test, three-point bending and investigation of biological behavior were employed. The fabricated scaffolds showed high compressive strength with favorable percentage of porosity. Thus, it might be concluded that the polymer foam fabrication technique can be appropriate for producing bone scaffolds. By increasing the weight percentage of hydroxyapatite from 45 to 65, the density of the scaffold increased from 1.37 to 1.57 g/cm3 and compressive strength increased from 0.82 to 1.7 MPa while the porosity decreased from 57.8 to 34.39.

Shape memory polymers been developed in the past years as a valid alternative to more traditional shape-memory materials. Shape memory polymers belong to a class of very smart materials that have the ability to remember their original shape. This advanced functionality makes shape memory polymer suitable and promising materials for diverse technological applications, including sensors and actuators particularly including the fabrication of smart biomedical devices. The polymers deform into a temporary shape and returns to its original shape by external environmental stimuli such as chemicals, temperature or pH. Therefore, a temperature-sensitive shape memory polymer is one that undergoes a structural change at a certain temperature called the transition temperature. A change in shape caused by a change in temperature is called a thermally-induced shape memory effect. Shape-memory research was initially founded on the thermally-induced dual-shape effect. This concept has been extended to other stimuli by either indirect thermal actuation or direct actuation by addressing stimuli-sensitive groups on the molecular level. This paper is intended to serve as a brief review of key concepts associated with shape memory material. This review describes the fundamental aspects of molecular design of suitable polymer architectures, tailored programming and recovery processes, with the focus being on the structure of thermally sensitive shape memory polymers.

The effect of modified starch on the properties of poly(styrene-ethylenepropylene- styrene) tri-block copolymer was studied. Chemical treatment of starch with maleic anhydride was accomplished in an internal mixer in the presence of glycerol. The reaction was confirmed using Fourier infrared spectroscopy (FTIR) and titration. The blend samples containing 10, 20, 30 and 50 wt% were obtained by melt blending and their mechanical, morphological and dynamic-mechanical properties were studied. Scanning electron microscopy (SEM) images displayed droplet-matrix morphology and with increases in modified starch up to 50 wt% some partial co-continuous morphology was also observed. With increase of modified starch in the compound, the size of dispersed phase increased. DMTA results revealed that the partial compatibility was obtained because of slight difference between glass transition temperatures of two phases in the presence of modified starch. The peak of modified starch shifted to higher values and the differences between the two peaks decreased, indicating partial compatibility. Mechanical properties including tensile, elongation-at-break and modulus were also determined and the results showed that the mechanical properties of the sample were higher than those of neat TPS because of the higher compatibility. Tensile strength was decreased with increase in modified starch content due to the absence of strong interfacial adhesion. Moduli of the samples were increased with increase in modified starch content due to higher stiffness of starch. Biodegradability of the samples was evaluated by weight loss percentage using compost test. A rapid degradation was observed in the first 45 days and with increase of the modified starch content the degree of degradation was increased.

Production of Biodegradeable composites manufacturing in recent years has caused extensive studies in the field of optimization and more applications. Production of multi-component composites with biopolymer materials can resolve Problems caused by non-return of polymeric materials on the natural cycle. Biopolymer materials, reduces mechanical and rheological properties of the nanoparticles helps to improve these properties. In this study, nanoparticles of titanium dioxide to the composite polyethylene / starch percentages of 30, 40 and 50 of the biopolymer starch were added and mixed in a twin-screw extruder. Mechanical, rheological and biodegradability Properties of the composite were studied. The results show that the elongation at rupture in nano-composite polyethylene / starch, containing 30% and 50% starch, by 92/74% and 37/91%, while the amount of the polyethylene net is 122%. Titanium dioxide nanoparticles in the polymer matrix of the composite polyethylene / starches such suppliers are compatible.
Environmental degradation properties of nanocomposites also increased by increasing the percentage of starch.

One of the major concerns of using a non-biodegradable polymer product is its disposal at the end of its life cycle. Development of biodegradable plastics promises an alternative solution to combat this problem. Blending of poly(lactic acid) with non-biodegradable polymers is a practical and economical method for modifying the biodegradability properties of non-biodegradable polymers. In this study, soil biodegradability of the blends of high density polyethylene (HDPE) and variable amounts of recycled poly(lactic acid) (r-PLA) plastic flakes at 0, 5, 10, 20, 30, 40 and 50 wt% was studied. The behavior of the force-elongation profile of the blends having r-PLA content of lower than 30 wt% was approximately the same as that of pure HDPE while, it was completely different for the other blends. Tearing force and elongation-at-yield-point of the blends films with the 20 to 50 wt% r-PLA were decreased significantly after 60 days of soil biodegradability test. Morphological study showed that biodegradability of the blend films at surface of the samples (deep pores and grooves) was increased with extended biodegradability time and higher r-PLA content, while, this variation was significant for the blend films of more than 20 wt% r-PLA content. Thermal properties evaluation by differential scanning calorimetry (DSC) curves indicated that the glass transition temperature and enthalpy peaks during the heating stage were eliminated with increasing the biodegradability testing time. Also, reduction in the crystallinity degree of the r-PLA component with increasing the biodegradability testing time coincided with the earlier results.