ORGANICALLY MODIFIED LAYERED CLAYS

LATEX STAGE MIXINGMELT MIXING

ROSE MARIA

2ND M.Sc BPSCBPST, KOCHI

• In the manufacture of rubber product it is reqirement to add various quantities of fillers,

plasticizers, curatives and other ingredients prior to the vulcanization step. Intimate mixing

of the ingredients call for energy consuming and expensive equipments like two roll mixing

mill.

• Further it is very difficult to disperse the different ingredients and there are chances of fine

powders going into the surrounding air. This lead to health concerns due to inhalation and

environmental pollution.

• Latex stage compounding offers a potential alternative in rubber product manufacture due

to these major concerns of energy consumption, health hazards, increased labor and

environmental problems as the method is easy and simple.

LATEX STAGE MIXING

A Schematic of formation of the nanocomposites through latex

compounding Method.

• Being known that a large number of rubbery polymers that need to be used in blends are available

commercially as natural, synthetic or artificial lattices, there exists the possibility of a simple and

environmental friendly means for production of latex based nanocomposites. By latex stage compounding

there is the possibility of using prevulcanized latex can directly be converted into nanocomposites.

Factors :-

The factors affecting the final dispersion level of clay in nanocomposites prepared

by latex mixing mainly include (1) the size of the rubber latex, (2) the ratio of

rubber latex to clay suspension, (3) the processing approach of co- coagulation,

and (4) the interaction between rubber(latex particles) and clay layers.

Apparently, the smaller the size of the latex particle and the higher the latex

content, the better dispersion would be achieved. Nevertheless, these two factors

could not be adjusted flexibly when the rubber clay nanocomposite were

prepared with LCM.

Latex Stage Blending of Natural Rubber and Poly(Vinyl

Chloride) for Improved Mechanical Properties

Polyvinyl chloride is one of the most widely used polymers because of

its low cost and design advantages. It has the number one position in

overall product volume and number of applications. Modifying

elastomers by blending with PVC is one of the promising methods of

improving the oil, ozone and fire resistance of rubber vulcanizates. Modulus, hardness

and flame resistance of natural rubber can

be significantly improved by blending with PVC , but developing

moderate mechanical properties is a problem due to the immiscible

nature of the two polymers. However, certain additives are capable

of improving the miscibility of these polymers . The incorporation

of plasticizers in the blend was found to promote miscibility. The

mechanical properties of an immiscible blend are strongly dependent

upon the blending method used.

Blending Natural Rubber and PVC in the latex stage is a promising

method for improving the mechanical properties of the blends.

Amine terminated natural rubber is an efficient compatibilizer for the system. The

thermal ageing resistance, oil resistance and the processing behavior of the latex

stage blend are superior to those blends prepared by direct mixing of the solid

polymers.

Carboxylated acrylo nitrile butadiene rubber latex/

kaolin nanocomposites: preparation and properties

Carboxylated nitrile butadiene rubber (XNBR)–based nanocomposites with varying amounts of

nanokaolin were produced by latex stage mixing. Sonication of the

unmodified kaolin and the technique adopted for the preparation of the composite have

helped to get a uniform dispersion of clay in XNBR matrix. Nanokaolin caused enhancement in

the mechanical properties of the composites. Proper dispersion of the clay particles, partial

exfoliation/intercalation of clay, and interaction of clay with the polar rubber latex made

nanokaolin good reinforcing filler in XNBR latex.

Swelling studies conducted in methyl ethyl ketone showed a decrease in the swelling index

and solvent uptake confirming the hindrance exerted by clay and the possible clay–rubber

interaction.

Increase in complex modulus obtained from the strain sweep analysis is a further evidence

for better rubber filler interaction.

The composites were characterized by the scanning electron microscopy,

X-ray diffraction analysis, and atomic force microscopy.

• Melt processing is a common alternative that is particular useful for dealing with

thermoplastics polymers.

• Carbon nanotubes can be mixed into the polymer melt by shear mixing.

• Melt blending is sometimes less effective at dispersing nanotubes in polymers

because nanotubes can effect melt properties such as viscosity.

• The shear force of the melt mixing method was favorable for the homogeneous

dispersion of MWNTs.

MELT MIXING

• Among the many currently available rubber compounding

techniques,the melt compounding method is the most widely

applied method for preparing Rubber – Clay Nanocomposite.

• For successful preparation of RCNs via melt compounding

requires that the clay is first organically modified in order to

(1) reduce its hydrophilicity and

(2) facilitate intercalation of the rubber chains into the gallery of clay

layers.

MECHANISM

Melt mixed compatibilized polypropylene/clay nanocompositesthe effect of compatibilizers on optical transmittance and mechanical properties

Polypropylene (PP)/clay nanocomposites were prepared via a melt mixing technique.

Two types of compatibilizers, polyolefin elastomer grafted maleic anhydride (POE-g-MA),

and polypropylene grafted maleic anhydride (PP-g-MA) were incorporated to improve

the dispersion of commercial organoclay (20A). With the introduction of PP-g-MA, the

optical transmittance of the nanocomposites displayed higher transmittance than those

of the POE-g-MA compatibilized case. However, POE-g-MA greatly increased the

interlayer spacing of the clay compared with PP-g-MA. This interesting observation is

pertinent to the complex morphology of compatibilized nanocomposites.

The PP-g-MA compatibilized system conferred higher tensile strength, Young’s modulus, and cutting

strength than the POE-g-MA compatibilized case. The high cutting strength of the PP/clay

nanocomposites, with or without compatibilizers, signified the importance of crystalline yielding even

in the nano-fracture zone of deformation. This finding has not been published in the literature of this

field. Clay and its dispersion effect that conventionally claimed to enhance the tensile properties were

rather insignificant under this condition of confined deformation of the cutting design. The current

results suggest that a high extent of exfoliation may not guarantee high transparency or strength for

nanocomposites. The matrix properties and interphase whose variations were caused by the

additional compatibilizers to aid the clay dispersion were also crucial factors to the derived properties.

POLYMER MELT INTERCALATION

Polypropylene (pp) is one of the most widely used polyolefin polymers. Therefore, it has been attractive to

synthesize a PP-Montmorillonite nanocomposite.

A PP nanocomposite would be formed by heating a mixture of PP and organophilic montmorillonite above

the melting temperature of PP(about 160º C ). The Nanometer dispersion of silicate layers in a PP matrix was

not realized even by using a montmorillonite treated with a dioctadecyldimethylammonium ion (DSDM- Mt),

in which the polar surfaces of the clay mineral should be covered with one of the most hydrophobic

alkylammonium ions.

How to introduce nanotubes into polymers

• Suspensions of nanotubes in polymer solutions, preparation as thin

films

• In-situ polymerization in presence of nanotubes

• Melt mixing of nanotubes with polymers

MWNT are produced as agglomerates SWNT are produced as bundles

Melt mixed composites where two ways of introducing nanotubes in polymer matrices were

used. In the first case, commercially available masterbatches of nanotube/polymer composites

are used as the starting materials that are diluted by the pure polymer in a subsequent melt

mixing process (masterbatch

dilution method) while in the other case nanotubes are directly incorporated into the polymer

matrix. As an example of the masterbatch dilution method, composites of polycarbonate with

MWNT are presented which are produced using a Brabender PL-19 single screw extruder. In this

system, electrical percolation was found at about 0.5 wt% MWNT.

Melt Mixing as Method to Disperse CarbonNanotubes into Thermoplastic Polymers