Literature survey on polymer nanocomposite ravinaraian pandey
LITERATURE SURVEY ON POLYMER NANOCOMPOSITE. RAVI NARAIAN PANDEY M Tech.-2 nd year. DTU—DELHI.
INTRODUCTION The particles with small size in the range from a few to several tens of nanometers are called quasi zero-dimensional mesoscopic system, quantum dots, quantized or Q particles, etc. According Jordan et. al (2004) the nano-sized inclusions are defined as those that have at least one dimension in the range 1 to 100 nm.
NANOCOMPOSITE STRUCTURE In general, the structure of polymer/clay nanocomposites are classified according to the level of intercalation and exfoliation of polymer chains into the clay galleries. Various parameters including clay nature, organic modifier, polymer matrix and method of preparation are effective.
PHASE SEPARATED STRUCTURE. When the organic polymer is interacted with inorganic clay(unmodified),the polymer is unable to intercalate within the clay layers and the clay is dispersed as aggregates or particles with layers stacked together within the polymer matrix. The obtained composite structure is considered as “Phase separated”.
INTERCALATED STRUCTURE. When one or more polymer chains are inserted into the inter layer space and cause to the increasing of the inter layer spacing , but the periodic array of the clay layer is still exist ,the intercalated nanocomposite is formed.
EXFOLATED STRUCTURE. Exfoliated or delaminated structure is obtained when the insertion of polymer chains into the clay galleries causes to the separation of the layers one another's and individual layers are dispersed within the polymer matrix.
PREPARATION OF POLYMER/CLAY NANOCOMOPOSITES. Many efforts have been made for the preparation of intercalated and exfoliated polymer/clay nanocomposites with improved properties. A wide variety of polymer characteristics including polarity, mol. Wt, hydrophobicity, reactive groups as well as clay characteristics such as charge density and its modified structure and polarity are effective on the intercalation of polymer chains within the clay galleries.
SOLUTION INTERCALATION. This is based on a solvent system in which the polymer is soluble and the silicate layers are swellable. The silicate layers is first swollen in a solvent ,such as chloroform. When the polymers and layered silicate solutions are mixed ,the polymer chain intercalate and displace the solvent within the remains ,resulting in nanocomposite.
INSITU INTERCALATIVE POLYMERIZATION. In this method ,the layered silicate is swollen within the liquid monomer ,or a monomer solution, so the polymer formation can occur between the inter calated sheets. polymerization can be initiated by heat or radiation, by the diffusion of suitable initiator or by organic initiator.
TEMPLATE SYNTHESIS . This method is particularly adapted to water soluble polymers and some attempts have been achieved with polymers such as poly(vinyl pyrrolidine),HPMC,PANI,and PAN etc. The method for in situ hydrothermal crystallization of a polymer hectorite nanocomposite consist in refluxing for 2 days a 2 wt ℅gel of silica sol, MGOH sol , LIF and desired polymer in water.
MELT INTERCALATION. Clay is mixed within the polymer matrix in molten temperature .The conventional methods such as extrusion and injection molding are used for dispersion of clay layers within the polymers matrix.
THERMOPLASTICS NANOCOMPOSITE. Thermoplastics such as Polypropylene, Polyethylene ,Ethyl vinyl acetate, Ethylene propylene diene monomer ,Polyamide ,Poly ethylene terpthalate and polystyrene have been used as polymer matrices for the preparation of nanocomposites.
ELASTOMERIC NANOCOMPOSITES. Burnside and giannelis have described the two step preparation of silicone rubber based nanocomposites .first, silanol-terminated poly(dimethyl siloxane) (Mw=18000) was melt blended at room temperature with dimethyl –ditallow ammonium –exchanged MMt, followed by cross linking of the silanol end groups with tetra ethyl ortho silicate.
THERMOSET NANOCOMPOSITES. In situ polymerization has also been used for the preparation of different of different thermosets nanocomposites. The studies of epoxy system considered the ring opening polymerization of epoxides to form polyether nanocoposites.
BIO DEGRADEBLE NANOCOMPOSITES. Natural and biodegradable polymers are a new generation of polymers that are relatively friendly to the environments with little or no impact when disposed.e.g. PLA, Starch,Cellulose etc.
KEY FACTORS DURING SURVEING. (1) XRD and TEM are used routinely to measures basal spacing of organ clays, and by inference to determine the conformation of the surfactants hydrocarbons chains. No one has attempts to study the relationship between the spatial distributions of charge within the clay lattice and surfactants structure.
(2)Wetting of organ clay is essential conditions ,but not a single study exists in the literature in which attempts has been made to measure the critical surface energy of the organoclay surface.
(3)Lack of recognition within the nanocomposite community that the organoclay structure is in fact a lamellar liquid crystal.
CONCLUSION. Polymer reinforced with as little as 2-5wt ℅ of nano-particles via polymerization exhibits dramatic improvements in thermo-mechanical properties, barrier properties and flame retardency.
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