APPLICATION OF LAYERED AND NON-LAYERED NANO/MICRO PARTICLES IN

POLYMER MODIFICATION

ARJUN K GOPI2ND M.Sc BPSCBPST, KOCHI

POLYMER MODIFICATION

The modification of polymers is interdisciplinary in nature cutting across traditional boundaries of chemistry, biochemistry, medicine, physics, biology and materials science and engineering.

Because of this interdisciplinary nature, persons involved with polymer modification should be broadly trained to permit the best application of revealed information.

Polymer modifications are intended to impute different, typically desired properties to the new modified material--properties such as enhanced thermal stability; multiphase physical responses; biological resistance, compatibility or degradability; impact response; flexibility; rigidity; etc.

Advantages of polymer modification:-1. The application of experimental design, statistical design to allow rapid experimental testing of polymers.

2. Advances in the thermodynamics of polymers and the thermodynamics of miscibility.

3. The development of predictive capacity of polymer properties and behaviour based on field models of molecular interactions.

4. Development of the theory controlling the processing of polymers.

5. Modeling of the polymeric solid.

6. New methods to form polymers including coextrusion, pultrusion, and production with internal reinforcement.

APPLICATION OF NON-LAYERED NANO-PARTICLES IN POLYMER MODIFICATION

INTRODUCTION

Polymer nano composite can be considered as an important category of organic-inorganic hybrid materials, in which inorganic nanoscale building blocks(e.g., nanoparticles, nanotubes, or nanometer thick sheets) are dispersed in an organic polymer matrix.

When compered to conventional composite based on micrometer-sixed fillers, the interfase between the filler particles and matrix in a polymer nanocompositeconstitutes a much greater area within the bulk material, and hence influence the composites’s properties to a much greater extent, even at a rather low filler loading.

Currently numerous producers for the preparation of polymer nanocomposite have been proposed, using the following approaches:-

1. Direct incorporation of nanoscale building blocks into a polymer melt or solution.2. In-situ generation of nanoscale building blocks in polymer matrix.3. Polymerization of monomers in he presence of nanoscale building blocks.4. A combination of polymerization and formation of nanoscale building blocks.

The key issue of these techniques is that the geometry , spatial distribution, and volume content of nano fillers must be effectively controlled through adjusting the preparation conditions so as to ensure the structural requirements of nanocomposites stated above.• Its noteworthy that the problem with dispersive mixing is that the nano particles commercially

available usually exist in the form of agglomerates, which are difficult to disconnect by limited shear force during mixing.The latter will maintain their friable structure in the composite and can hardly provide property improvements at all.

• Nanoparticles can be pretreated by irradiation to introduce grafting polymers onto their surface not only outside but also inside the particle agglomerates.

• The surface of the nanoparticles will also become “hydrocarbonated” due to an increased hydrophobicity resulting from the grafting polymer.

• This is beneficial for the filler/matrix miscibility and hence for the ultimate properties.• In case of a thermosetting matrix polymer, the grafted nanoparticles will keep their more

stationary suspended state due to the interaction between the grafting polymer and matrix.• After curing such a miture , the filler/matrix adhesion would also be substantially enhanced by

chain entanglement and/or chemical bonding between the grafting polymer and the matrix material.

• Lets discuss about Application of silica nanoparticles in the modification of polypropylene and epoxy resin.

Application of silica nanoparticles in the modification of polypropylene

and epoxy resin.

Preparation of PP-Based nanocomposites and their characterization

• PP-based nanocomposites were reoared by tumble mixing the preweighed quantities of PP and grafted fillers, followed by compounding this mixture on lab scale single screw extruder.

• Temperature : 200⁰C And screw RPM 25• The specimens for mechanical tests were machined from compression molded

plates(65X45X3 mm3) of extrudates.• The filler volume fractions could be computed from the known weights of the polymer matrix,

The fillers and the polymer introduced by irradiation.• The reinforcing efficiency of the nanoparticles agglomerates was assessed by measuring of the

Young’s modulus , tensile yield strength and impact strength.• Tensile test is carried out on dumbbell shaped specimens by UTM at a crosshead speed of

10mm/min.• The fractured surfaces were observed by SEM.• And XJJ-5 Tester was used for unnotched charpy impact strength measurements.

Preparation of epoxy-Based nanoparticles and their characterization

• Epoxy-based nanoparticles were prepared by mixing the preweighed quantities of epoxy and grafted fillers at 80⁰C with stirring for 2h and sonication for 1h.

• Then the mixture was heated to 130⁰C and the curing agent DDS was added under stirring for 10min.(for curing the composites, the following procedures was carried out step by step: 3h at 100⁰C, 2h at 140⁰C,2h at 180⁰C, and 2h at 200⁰C.

• The curing behaviour of the epoxy and its composites was examined by DSC at a heating rate of 2⁰C/min.

• Unlubricated sliding wear tests were carried out on a block on ring apparatus under a pressure of 3MPA and a constant velocity of 0.4m/s.

• The specific wear rates were calculated from weight measurements of the specimens before and after the actual steady test period.

• The morphologies of the worn surfaces were observed with SEM.

Effect of Irradiation grafting polymerization on the nanoparticles

• In order to establish the effect of modified nano-silica on the mechanical behaviour of PP composites, the variation in the chemical structure of the particles should be known at the very beginning of the discussion.

• FTIR spectra of untreated and treated nano-silica are shown Below:-

• To eliminate the influence of homopolymers, both polystyrene-grafted nano-Sio₂(Sio₂-g-PS) and poly(ethyl acrylate)-grafted nano-Sio₂(Sio₂-g-PEA) used for the FTIR examinations were separated from the homopolymers in advance.

• Compared to the spectrum of Sio₂ as-received, the adsorptions at 690, 1460, 2960 cm⁻ⁱ appearing in the spectrum of Sio₂-g-PS represent the bending mode of C-H in benzene rings and the stretching ,odes of C-C and C-H , respectively.

• In addition the band at 1725 cm⁻ⁱ in the spectrum of Sio₂-g-PEA indicates the existence of carbonyl groups.

• These bands prove that PS and PEA have been chemically bonded to the nano-silica during the irradiation polymerization.

Tensile Properties

Typical tensile stress strain curves of neat PP and its filled versions are Shown Below:-

• As Expected both a reinforcing and a toughening effect of the nanoparticles on the polymeric matrix were fully brought into play.

• That is a structural weakness, that would have been expected from the agglomerating behaviour of the nanoparticles, could be fully eliminate by the grafting of macro molecular chains onto the individual particles.

CONCLUSION

• The modification of nanosilica by means of grafting polymerization helps to impart a balanced performance of the composites.

• The addition of grafted silica nanoparticles into PP can bring in both reinforcing and toughening effects at rather low filler contents.

• Such a simultaneous improvement in modulus, strength, and elongation to break is hard to observe in conventional micron sixed particulate composites.

• Grafting polymerization onto nanosilica can also increase the interfacial interaction between the particles and epoxy matrix through chemical bonding.

APPLICATION OF LAYERED NANO-PARTICLES IN POLYMER MODIFICATION

INTRODUCTION

Manufacturers fill polymers with particles in order to improve the stiffness and the toughness of the materials, to enhance their barrier properties, to enhance their resistance to fire and ignition or simply to reduce cost. Addition of particulate fillers sometimes imparts drawbacks to the resulting composites such as brittleness or opacity.

Nanocomposites are a new class of composites, that are particle-filled polymers for which at least one dimension of the dispersed particles is in the nanometer range.One can distinguish three types of nanocomposites, depending on how many dimensions of the dispersed particles are in the nanometer range. When the three dimensions are in the order of nanometers, we are dealing with isodimensional nanoparticles, such as spherical silica nanoparticles obtained by in situ sol-gel methods or by polymerization promoted directly from their surface

Nanocomposite preparation

• In situ intercalative polymerization: In this technique, the layered silicate is swollen within theliquid monomer (or a monomer solution) so as the polymer formation can occur in between theintercalated sheets. Polymerization can be initiated either by heat or radiation, by the diffusion of a suitable initiator or by an organic initiator or catalyst fixed through cationic exchange inside the interlayer before the swelling step by the monomer.

• . In a typical synthesis, the modified montmorillonite (12-Mont) was mixed with the monomer in a mortar. A small amount of 6-aminocaproic acid was added as a polymerization accelerator when the relative amount of 12-Mont used was smaller than 8 wt.% (relative to 12-Mont). The mixture was heated first at 100⁰C for 30 min then at 2508C for 6 h. The cooled and solidified product was crushed, washed with water at 80⁰C, and then dried.

PROPERTIES

Layered silicate nanofillers have proved to trigger a tremendous properties improvement of thepolymers in which they are dispersed. Amongst those properties, unexpected large increase inmoduli (tensile or Young's modulus and flexural modulus) of nanocomposites at filler contentssometimes as low as 1 wt.% has drawn a lot of attention.

Thermal stability and fire retardancy through char formation are other interesting and widely searched properties displayed by nanocomposites. Those new materials have also been studied and applied for their superior barrier properties against gas and vapor transmission. Finally, depending on the type of polymeric materials, they can also display interesting properties in the frame of ionic conductivity or thermal expansion control.

CONCLUSION

The large array of improved thermo-mechanical properties attained at very filler content(5 wt.% or less) together with the ease of production through simple processes such as meltintercalation, directly applicable by extrusion or injection molding make layered silicate-basednanocomposites a very promising new class of materials.

They are already commercially available and applied in car and food packaging industries. Undoubtedly, the unique combination of their key properties and potentially low production costs paves the way to much broader range of applications.

Furthermore, the quite low filler level required to display sizeable properties enhancement makes them competitive with other materials.