Sharif Digital Repository

Polypropylene is a commodity thermoplastic with good physical and mechanical properties along with fair recyclability and cost. However, the application of polypropylene is limited in some cases, especially in automotive industry, as a result of inappropriate toughness of this material. Although rubber toughening of polypropylene is a method used to increase the toughness, it reduces scratch resistance. Studies performed in the polymer group of this department reveal that the cavitation resistance of elastomeric phase and its bonding to the matrix are two effective parameters in scratch resistance of this material. In this study, it is tried to alter the cavitation resistance of elastomeric... 

In recent years the rapid rise of polymer consumption especially in the form of packaging materials became a real menace for the environment. Polyolefin are some of the most dominant packaging materials and responsible by part of the problems in the disposal of one-trip packaging. One of the possible ways of solving this problem is the introduction of additives increasing their susceptibility to environmental degradation into non-biodegradable polymers. One such additive is starch- the natural, cheap, and easily biodegradable polymer. Starch was already used as a filler or as a blend with polyolefin. Addition of dry starch granules to polyolefin follows the general trend of filler effects on... 

Polypropylene/clay nanocomposites are considered as a group of widely used nanocomposites in industrial applications due to their desired properties, yet reasonable cost. However, dissimmilar chemical nature of polypropylene and clay do not allow perfect dispersion of silicate layeres in the matrix and thus restricts full advantages of these composites.An earlier investigation in this group considered solving this shortcoming through incorporation of PA6 as an intermediate phase to enhance clay platelets dispersion. The current project follows this route via studing the influence of molecular weight of the PP matrix, compatibilzer and the mixing procedure of the compound. To investigate the... 

Bone scaffolds are combinations of several materials, for achieving suitable properties and usage for replacing with defected bone. In this study, TCP/Agarose scaffolds are fabricated by two different approaches. The first one is using polymer sponge and gel casting technique and the other one is using foaming agent in order to obtain scaffolds with same porosity. The results show that in spite of same structure and porosity, scaffolds have different mechanical properties due to their different morphologies. Compressive strength of the scaffolds which were fabricated using polymer sponge method is 2.25MPa and elastic modulus is 56.8MPa. After coating with Agarose, compressive strength... 

This project aimed to fabricate the bone scaffolds with applying thermoplastic starch-based nano-biocomposites. The starting materials for this scaffold are as follows: thermoplastic starch, ethylene vinyl alcohol as the polymer matrix and nanoforsterite as the ceramic reinforcing phase. Furthermore, vitamin E was used as antioxidant for preserving starch against thermo-mechanical degradations. Likewise, 3D pore structure was developed using azo-dicarbonamide and water in injection moulding process. With blending thermoplastic starch and ethylene vinyl alcohol, some thermoplastic starch’s properties including degradation rate and water absorption were modified. In addition, having... 

Blending different polymers to achieve a compound with modified Physical physical and mechanical properties, has interested researchers for years. Among all, LDPE and HDPE have attracted a great attention for this purpose; specially when a mineral filler like clay is another part of composite. In the related literature, it is proven that small amounts of clay can improve physical and mechanical properties in comparison to virgin blend. Focus of this research is on HDPE/EVA/Clay nanocomposite and its physical and mechanical properties. Having vinyl group, EVA is a compatibilizer that makes clay to disperse better; EVA can also makes the brittle HDPE tougher. At first, HDPE/EVA blend... 

Due to the negative effects of conventional plastics on the environment, especially in the packaging sector, extensive efforts have been put to replace these polymers with biodegradable polymers. Starch is one of the biodegradable polymers which has attracted a lot of attentions because of low cost and good process ability. Native starch has the form of granule and can be processed to a continuous phase after gelatinization in the presence of a plasticizer. The resulting material is a biodegradable plastic-like material called thermoplastic starch (TPS) which is processed using conventional technologies, but suffers from low mechanical properties and high hydrophilicity. Addition of... 

Melt blending of polymers is a rather cheap and easy approach for obtaining new set of properties compared to synthesizing new polymeric materials. For the same reason, binary and ternary polyethylene blends are made to provide added value for different applications. Polyethylene blends are commonly composed of high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE). Although the Mechanical and physical properties of polyethylene binary blends have been studied extensively, microstructure and mechanical properties of polyethylene ternary blends have been the subject of very few studies. In this work, samples with 40-60 Wt. % HDPE and... 

Tissue regeneration by bio-compatible/degradable scaffolds is one of the widely used approaches in the field of tissue engineering. In this study, a thermoplastic starch based nanocomposite scaffold with gradient structure was fabricated by unidirectional freeze drying method. To increase the stability of the scaffold in the aqueous media, PVA was added to starch solution. Then, the PVA and starch molecules were cross-linked by adding citric acid to the mixture. On the one hand, to improve the mechanical properties of the scaffold, and control its bio-degradability on the other, cellulose nano-fibers were employed. Also, the bioactivity of the scaffold was induced by using hydroxyapatite... 

Epoxy resins are relatively brittle and have low resistance to crack propagation. It is common to add rubber particles to improve crack resistance in epoxies, although these particles may deteriorate the strength of the matrix. Different nanomaterials are used to overcome the inherent brittleness of epoxies and to keep the mechanical properties. Among them, carbon nanotubes has been attracted many attentions. Fractue behavior and mechanical properties of two kind of novel nanocomposites, i.e, epoxy/carbon nanotube and epoxy/rubber/carbon nanotube are investigated in current study. Electron microscopy investigations were done to assure the CNTs distribution and fracture mechanisms as well.... 

It is a common method to use some proper materials such as honey, herbal fibers, and minerals for covering the wounds as an effective treatment. Nowadays biopolymers and new methods of nanofiber production to build a structure similar to the natural extracellular matrix (ECM) like electrospinning are used to reduce the time of restoration and prevent from the effects of wounds such as bedsores, diabetic ulcers, and severe burns. For effective design of a wound dressing, wound feature, recovery time, physical, mechanical, and biological properties should be considered in order to best as possible heal the bound. In this research, cellulose nanocrystals with average aspect ratio of 11.8 and... 

Epoxy resins have good mechanical and thermal properties, high chemical resistance and low shrinkage during cure but in spite of these good properties,they are brittle and this limits the usage of them. Adding a second, soft or rigid, phase has been always an effective strategy to improve the toughness of epoxy. Rigid phase used in resins are divided into organic and inorganic. The aim of this study is to increase epoxy toughness, maintaining mechanical properties and study effect of silica and polycarbonate on fracture toughness simultaneously. Mechanical properties including yield strength and elastic modulus are evaluated by pressure test. Additionally fracture toughness and three... 

Strain softening after the yield point is a prevalent phenomenon in the stress-strain response of cellular solids, consisting of porosities in micro/macro-meter scale, as well as polymers, consisting of free volumes in sub-nanometer molecular scale. Although the underlying micromechanisms for softening in cellular solids are already known, the molecular origin for softening in polymers is still unknown. In this thesis, the micromechanisms of the softening in both materials are investigated. Then, a hypothesis is raised and evaluated to connect the nano-mechanics of softening in polymers to the micro-mechanics of softening in cellular solids. Experiments of compression test, positron-based... 

Polypropylene block copolymer is used in different industries like pipe productions. This copolymer has proper mechanical properties, specially it has good impact strength, but in some applications it’s elastic modulus (stiffness) is not enough and that leads to some problemes in servise. Nucleating agents influence crystalline structure and properties and also the mechanical properties by controlling the crystallization process. Nanoparticles also have a beneficial effects on physical and mechanical properties. In this study, the effect of adding two types of α-phase nucleating agents (commercial names NA11 and DMDBS) in the form of masterbatch wt 5% with a carrier of polypropylene block... 

Polymer blending has an important role in preparation of materials with suitable properties without synthesizing new polymers. One of these blends is polypropylene (PP)/ polyethylene (PE). PE is added for improving the impact strength and toughness of PP. For improvementof the properties, a compatibilizer is used due to incompatibility of the PP/PE blend. Improving the impact properties is usually related to the reduction in stiffness. Considering the importance of stiffness in many industrial applications, mineral fillers are employed for increasing the stiffness. In this research, the goal has been to manufacture polypropylene-based ternary composite(Polypropylene/ Polyethylene/Nanometric... 

Polypropylene (PP) is a fast growing polymer, particularly in automotive industry, where PP compounds have replaced many different parts made of conventional materials. In the first step, PP-g-MA, as compatibilizer, was synthesized. Two kinds of polypropylenes including a homo- and a block co-polymer were incorporated for this goal. Characterizations via titration and FTIR tests revealed higher degree of grafting reaction when homo-polymer was used for synthesizing PP-g-MA. In the next step, nanocomposites containing 3 wt% nanoclay with three different PP-g-MA/nanoclay ratios of 1:1, 2:1 and 3:1were made using a co-rotating twin screw extruder. Tensile, impact and XRD tests were performed to... 

Polypropylene (PP) is one of the most widely used commercial plastics in various industrial applications due to its desirable physical and mechanical properties and low cost. Engineering properties of this polymer depend very much on its crystalline structure. It is a common practice in polymer industry to modify crystalline structure by means of nucleating agents. Since nucleating agents are added in a rather low level to polymers, some investigators have tried this task in modifying crystalline structure of polypropylene by incorporating nucleating agent masterbatches. However, none have looked at the possible influence of the carrier resin in such masterbatches on the performance of... 

One of the most popular methods in order to protect foods is to package using various materials. By this act, the shelf life of the packaged foods may range from a few days to more than a year. Multiple types of plastics are being used as materials for packaging food, including polyolefin, polyester, polyvinyl chloride, polyvinylidene chloride, polystyrene, polyamide, and ethylene vinyl alcohol. Although more than 30 types of plastics have been used as packaging materials, polyolefin and polyesters are the most common. Biaxially Oriented Polypropylene (BOPP) is a polypropylene film that has been stretched in both the machine and cross directions. BOPP film has become one of the most popular... 

Polypropylene (PP) has a great market among the commodity thermoplastics. However, its application as an engineering plastic is limited due to the poor toughness and impact strength, especially at low temperatures and high deformation rates. To overcome this shortcoming, elastomeric modifiers have been used in engineering applications and thus rubber-modified PP blends have become a field of growing interest. In this regard, there have been great advances in blending technologies and also catalysts used for polymerization of olefins. Among these advances, the most applicable ones are impact polypropylene copolymers and also the advent of new types of olefinic copolymers that can replace EPR... 

The aim of this study is to investigate the effects of nanoclay and rubber particles morphologies on fracture behavior of a lightly cross-linked epoxy. In addition, the role of cavitation resistance of rubber particles on fracture behavior of the nanoclay-rubber-epoxy hybrids was studied. Two types of organoclay and three kinds of rubber modifiers (in micron and nano-size) were incorporated into the epoxy. The results obtained indicate that addition of either intercalated or exfoliated clay increases fracture toughness of the epoxy resin, although the increases in toughness are modest (a 50% increase). The microscopy examinations and the micromechanical models revealed that the...