Melt-mixing

Fabrication methods have overwhelmingly focused on improving nanotube dispersion because better nanotube dispersion in polyurethane matrix has been found to improve the properties of the nanocomposites. The dispersion extent of CNTs in the polyurethane matrix plays an important role in the properties of the polymer nanocomposites. Similar to the case of nanotube/solvent suspensions, pristine nanotubes have not yet been shown to be soluble in polymers, illustrating the extreme difficulty of overcoming the inherent thermodynamic drive of nanotubes to bundle. Therefore, CNTs need to be surface modified before the composite fabrication process to improve the load transfer from the polyurethane matrix to the nanotubes. Usually, the polyurethane/CNT nanocomposites can be fabricated by using four techniques melt-mixing (15), solution casting (16-18), in-situ polymerization (19-21), and sol gel process (22). 

Melt processing is a common alternative that is particularly useful for dealing with thermoplastic polymers and holds great interest because of the ease with which the process could be scaled up to industrial standards. Thermoplastic polyurethane nanocomposites can be fabricated by melt compounding of CNTs with polymer resin. Melt processing makes use of the fact that thermoplastic polymers soften when heated. Amorphous polymers like elastomer 

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PVC should not be melt-mixed with acetal polymers. These polymers are chemically incompatible mixing could cause rapid decomposition and gas evolution. 

Table 2. Melt-Mixed PVC Coating Powder Formulation ...

Subsequently, much improved thermoplastic polyolefin rubbers were obtained by invoking a technique known as dynamic vulcanisation. This process has been defined (Coran, 1987) as the process of vulcanizing elastomer during its intimate melt-mixing with a non-vulcanizing thermoplastic polymer. Small elastomer droplets are vulcanized to give a particulate... 

Fig. 3.15. Secondary ion images of blends the mass-resolved images pertaining to the mas-melt-mixed for 20 min (top) and 40 min (bot- ses listed below each image. Also shown are the...

Appendix B General Properties and Data on Elastomers and Plastics 175 Table B.IO True Stress at Break of Selected Melt-Mixed Rubber-Plastic Blends ... 

B.IO True stress at break of selected melt-mixed rubber-... 

Rubber blends with cure rate mismatch is a burning issue for elastomer sandwich products. For example, in a conveyor belt composite structure there is always a combination of two to three special purpose rubbers and, depending on the rubber composition, the curatives are different. Hence, those composite rubber formulations need special processing and formulation to avoid a gross dissimilarity in their cure rate. Recent research in this area indicated that the modification of one or more rubbers with the same cure sites would be a possible solution. Thus, chlorosulfonated polyethylene (CSP) rubber was modified in laboratory scale with 10 wt% of 93% active meta-phenylene bismaleimide (BMI) and 0.5 wt% of dimethyl-di-(/ r/-butyl-peroxy) hexane (catalyst). Mixing was carried out in an oil heated Banbury-type mixer at 150-160°C. The addition of a catalyst was very critical. After 2 min high-shear dispersive melt mix-... 

B. Preparation of Elastomer-Plastic Blend by Melt Mixing Without Vuicanization... 

Elastomer-plastic blends without vulcanization were prepared either in a two roll mill or Banbury mixer. Depending on the nature of plastic and rubber the mixing temperature was changed. Usually the plastic was fed into the two roll mill or an internal mixer after preheating the mixer to a temperature above the melting temperature of the plastic phase. The plastic phase was then added and the required melt viscosity was attained by applying a mechanical shear. The rubber phase was then added and the mixture was then melt mixed for an additional 1 to 3 min when other rubber additives, such as filler, activator, and lubricants or softeners, were added. Mixing was then carried out with controlled shear rate... 

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

In preliminary tests, melt mixed blends of PP and LCP were processed at six different temperatures (Tcyi 230, 240, 250, 260, 270, and 280°C) with a Brabender Plasti-Corder PLE 651 laboratory single-screw extruder. The measured melt temperatures were about 10°C higher than the cylinder temperatures (Tcyi). The objective was to study the influence of temperature on the size and shape of the dispersed LCP phase. Two different polypropylenes were used to ascertain the effect of the viscosity of the matrix on the final morphology. Different draw ratios were obtained by varying the speed of the take-up machine. 

Table 1 Designation and Temperatures of Subsequent Processing Steps for the Two Melt Mixed Blends...

Figure 2 Optical micrographs of melt mixed PP-LCP blends single-screw extruded at melt temperatures of (a) 250°C, and (b) 260°C.

TPEs from blends of rubber and plastics constitute an important category of TPEs. These can be prepared either by the melt mixing of plastics and rubbers in an internal mixer or by solvent casting from a suitable solvent. The commonly used plastics and rubbers include polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, ethylene propylene diene monomer rubber (EPDM), natural rubber (NR), butyl rubber, nitrile rubber, etc. TPEs from blends of rubbers and plastics have certain typical advantages over the other TPEs. In this case, the required properties can easily be achieved by the proper selection of rubbers and plastics and by the proper change in their ratios. The overall performance of the resultant TPEs can be improved by changing the phase structure and crystallinity of plastics and also by the proper incorporation of suitable fillers, crosslinkers, and interfacial agents. 

Greco et al. [50] studied the effect of the reactive compatibilization technique in ethylene propylene rubber-polyamide-6 blends. Binary blends of polyamide-6-ethylene propylene rubber (EPR) and a ternary blend of polyamide-6-EPR-EPR-g-succinic anhydride were prepared by the melt mixing technique, and the influence of the degree of grafting of (EPR-g-SA) on morphology and mechanical properties of the blends was studied. 

Conventional crosslinking agents, such as sulphur, accelerators, and peroxide, etc., used in dynamic vulcanization and melt-mixing of two polymers is the first step in the preparation of an EA. The dynamic vulcanization is done by dynamic shear at a high temperature to activate the process. 

PBAs are generally prepared by three commercial methods [57,124] latex mixing, solution mixing, and melt mixing. 

Compounding and palletizing of the latex blended material is sometimes done by melt mixing. In such cases precautions must be taken to avoid thermal and shear degradation of the blended polymer. 

Baker and Saleem [51] have reported on the reactive compatibilization of oxazoline modified PS and carbox-ylated polyethylene. The coupling reaction results in amide-ester linkages at the time of melt mixing. A schematic representation of the reaction is shown in Scheme 2. 

The graft polymer formed during melt mixing results in good interfacial adhesion between the phases. The... 

The TLCP used was a widely investigated one, Vectra A950, manufactured by Hoechst-Celanese. The PC was produced by Enichem under the tradename Sinvet 303. Table 3 lists the main properties of these materials according to the manufacturers. The materials were dried in a vacuum oven at 120°C for 4 h before processing. Prior to injection molding of the composite samples, two components were melt mixed by a ZSK, W P, Stuttgart, extruder with a constant weight ratio of PC-TLCP = 80 20 [23]. 

As already discussed (Section 2.2.1.3), interchange reactions are also implicated in the formation of random copolyesters exhibiting the most probable molar mass distribution when polyester blends are melt mixed. They are also involved in the randomization of block copolyesters taking place in the melt upon heating.2,m 211... 

A.Y. Coran s research on the melt-mixed blends of elastomer and thermoplastics with dynamic vulcanization... 

Commercial melt-mixed blends of EPDM and PP, dynamically vulcanized, Monsanto (Santroprene) Polyamide TPE, Atochem (Pebax)... 

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