فصلنامه بسپارش
سال نهم شماره 3 (پیاپی 32، پاییز 1398)

Due to the low weight and chemical resistance of polymers, compared to metals,the use of these materials in various industries has increased. On the other hand,due to the low strength in polymers, their reinforcement with micron/nanoparticles isnecessary. In recent years, one of the advances in plastics and composite industries hasbeen the development and commodification of polymer-based nanocomposites. The use ofpolymer blend nanocomposites based on thermoplastic polyolefin have been developed inengineering application such as automotive, airplane, household appliances and medicalapparatus. There are different processes such as extruder and internal mixer to fabricatenanocomposites. The limitation of these processes is the high cost, the multi-stage processfor sheet production and the amount of nano-sized reinforcement particles (at most 5 wt%).Recently, investigations have been done on friction stir processing for the fabrication ofcomposites and nanocomposites. To produce polymer composites and nanocomposites withfriction stir process, a groove with defined dimensions is machined in the base polymersheet and nanoparticles are improvised into this groove. Subsequently, a rotating tool isplunged into the sheet and traversed along the groove to disperse particles to the basematerial.

The carbon nanotubes (CNTs) including the single-walled carbon nanotubes (SWCNTs)and multi-walled carbon nanotubes (MWCNTs) have the desirable properties andhigh capacity for application in tissue engineering and scaffolding. However, the scopeof their efficiency and quality enhancement in the CNT-polymer composites is wide open.The inherent capability of CNTs in facilitating the cellular growth could reflect the threedimensionalscaffolds with the polymer surfaces, affecting the ultimate cultivation for thetissue regeneration of electroactive cells. The polymers make the CNTs more efficient andmodify the scaffolds' characteristics. In the current paper, the features of CNT, involved inscaffolds performance, which have been modified through natural polymers and synthesizedpolymers including conductive, dielectric, and manipulated polymers and the polymercomposites are reviewed. The combination of CNTs and different types of polymersimproved the scaffolds' characteristics such as mechanical and electrical properties,biodegradability, structure, porosity, toxicity, etc. Each polymer type in influencing thecharacteristics of CNT-incorporated scaffolds and the preparation method of respectivescaffolds improved some features and enhanced the quality of polymer-based scaffolds.

Stimuli-responsive materials based on thermochromic are a new class of smart materialsthat has received a great deal of attention in the recent decades. The importance ofsmart polymers or stimuli-responsive polymers is growing due to having properties suchas toughness, simple processability, flexibility, elasticity, biocompatibility as well as beingcapable of reversible chemical and physical changes in response to variable environmentalconditions relative to inorganic materials. The most important characteristics of thesepolymers are their microscopic response to small environmental changes and they canreturn to their initial state under further stimulus. These polymers may respond to severaltriggers such as light, temperature, mechanical factors, electrical and magnetic fields,polarity, enzyme, and biomolecules. Recently, the rapid advancements on smart materialswith thermochromic properties have become a promising field. A thermochromic materialcan be in the form of monomer or polymer, organic or inorganic compound, and a singleor a multi-component system. The color of these compounds can change spontaneously orcontinuously in response to changes in temperature in a reversible way which is as the resultof changes in light reflection, absorption or scattering properties. These materials could beused in several fields such as thermochromic papers, inks, sensors and thermometers.

Nowadays, due to the development of automated composite manufacturing processeson prepregs, it is necessary to recognize the main properties and factors affectingprepregs. After the precuring stage, the tack is one of the main characteristics of theprepregs, and this parameter is the viscoelastic properties of the prepreg bulk. The tackis the ability of prepreg to stick to itself or to other surfaces. Factors affecting prematuretack can be divided into two general categories of structural and process factors. Themost important structural factors is the type of resin, resin formulation, molecular weight,viscosity, degree of cure, fabric type, fabric architecture, temperature, volume of cavitiesand volatile content are mentioned. Also, the most important process factors are humiditycontent, aging, contact time, contact force, separation force, lay-up speed and angle. Thecohesive failure and interfacial failure of two mechanisms of failure have been proven intack of prepreg and these two mechanisms are capable of interchanging under differentconditions. Also, due to the lack of a standard test, several different methods, such asfloating roller, probe, rolling ball, peel, lap shear and loop tack test, are used to measurethe amount of tack. In this paper, the factors affecting the prepreg tack, different measuringmethods and different failure modes have been investigated.

A great amount of polyethylene terephthalate-based disposable products and theirdischarge in nature as waste plastics create serious environmental concerns. Themechanical recycling of these materials to some polyester-based products accounts onlya small fraction of the waste materials. As a suitable alternative, the chemical recyclingprovides methods to remove PET from environment, produces high-value-added materials,by returning them to the production process in accordance with the principles of sustainabledevelopment of ecosystems, and creates job and research opportunities. Several chemicalrecycling methods such as alcoholysis, aminolysis, glycolysis have been explored andnumerous research works have been carried out to find suitable degradable materials,produce applicable materials, find ecofriendly catalysts under economically operatingconditions. Despite a remarkable number of research attempts on different methods inchemical recycling studies, there are still a few industrial or even semi-industrial chemicalrecovery plants and very little information available on them. This current article brieflyreviews the different chemical recycling methods applied in PET recycling production, therelative importance and economical issues of each method, materials and products, and theoperational conditions.

Nowadays, the use of non-oil materials with desirable properties, and at the same timereducing the adverse environmental impacts, has become one of the most importantissues in industry. Chitosan, as one of the most abundant biopolymers in nature, hasunique properties, including high biocompatibility, non-toxicity, acceptable antimicrobialproperties, and excellent performance in terms of film formation. These propertieshave potentially made this biopolymer very useful in packaging industries, textile,pharmaceutical, and papermaking. In this regard, the purpose of this study is to investigatethe effective parameters on the mechanical properties of chitosan biocomposites. Theparameters such as type, concentration, pH, and functional groups of solvents are takeninto consideration in making composites that are used as polymer phase fasteners. Also,the effect of plasticizers on weight percentages to reduce the fragility of chitosan films isdiscussed in this study. It was observed that the addition of each of these materials, due totheir structure and molecular weight, weight percentage, distribution pattern at the matrixlevel, functional groups on their molecules affect the structure of chitosan polymeric chainsand can change the mechanical properties of a biocomposite.