Roll mixing

The compounding of CR with fillers and vulcanization ingredients was done by a laboratory size open two-roll mixing mill. All the weights are given in parts per hundred parts of rubber and the recipe for the CR compounds is given in Table 4. 

The container may be heated in a thermostatically controlled hot room or with a heating band. Care must be taken to prevent localized overheating. As the thermal conductivity of the material is poor, there is often a temperature gradient in the container leading to the outside being melted and the center being still solid. This can be corrected by roll-mixing the container. All the material needs to be molten prior to use. The can must not have any translucent lumps in it. 

As it is nowadays often no longer practical to use organic solvents, it is recommended to select a different technique such as roll-mixing or comilling with povidone. That this method is also capable of producing an amorphous distribution of phenytoin and many other active substances is shown in Fig. 46 and in Table 78. In which two roll-mixed preparations are corn-pared with the crystalline active substance and a solvent-coprecipitate by X-ray diffraction. 

Fig. 46 Effect of the roll-mixing process on the crystallinity of phenytoin [226] 1 Phenytoin without povidone 2 Phenytoin + povidone K 30 1 + 1 3 Phenytoin + povidone K 30 1 + 3...

There are at least theoretical solutions to these two problems. The large volume is less of a problem in dosage forms such as instant or effervescent granules of ibuprofen [505], while the use of large quantities of solvents can sometimes be avoided by using a solvent-free production process such as the roll-mixing process for triturations. 

Two-roll mixing is another traditional method of mixing which relies on somewhat primitive equipment and on the skills of the operator. It has never been possible to establish standard procedure for this process and batch-to-batch results vary widely. 

Compacting the mixes by conventional rolling damaged the sulfur crystal structure, which formed as the mix cooled, causing poor subsequent performance of the rolled mixes. 

FIGURE 2.74 (a) Cross-section of a Banbury mixer (b) Roll mixing blades in Banbury mixer. 

PVB) 100,000 (PCL) 35,000 Vulcan XC-72 conductive carbon black (5 vol%) CB roll-mixed blend films from THF solutions crystallization temperature of 41°C As above and also with fullerene (5 vol%)... 

Recently, a new technology for the devulcanization of sulfur-cured scrap elastomers was reported [36] using a material termed Delink [37]. Such technique of devulcanization was designated as Delink process. In this process, 100 parts of 40-mesh or finer crumb is mixed with 2 to 6 parts of Delink reactant in an open two-roll mixing mill. Delink reactant is a proprietary material, and its nature and composition was not disclosed. 

Compounding was performed in an open two-roll mixing mill (laboratory size). NR was first masticated on the two-roll mill for about 2 3 min followed by addition of the ingredients. Cure characteristics were analysed using an oscillating disk rheometer (Monsanto R-lOO) at a temperature of 150 °C. The composites were cured at their respective cure times in a hydraulic press under a pressure of about 120 bar at 150 °C. Aged samples were prepared by keeping the samples in a hot air oven at 70 °C for 7 days. ... 

In another study, it was reported that NR gum and CB filled compounds containing nano-ZnO have been prepared on a laboratory size two-roll mixing mill at a friction ratio of 1 1.25 as per ASTM D 3184-89 and the samples were... 

The compatibility between the phases of the blends is even more needed when these phases are recovered from previously manufactured products. T6th et al. [165] made an approach in improving the adhesion between the compounds and thus the mechanical properties of the resulting materials in waste polyethylene/crumb rubber blends by using compatibiUzing additives such as olefin-maleic-anhydride copolymers the preparation method consisted of two-roll mixing at temperatures of 145-180°C followed by compression molding at 180°C. 

The first step of manufacturing a membrane is to prepare a suitable rubber compound either in a Banbury internal mixer or in an open two roll mixing mill by adding different compounding ingredients in the proper sequence during the mixing operation to get a well dispersed compound. 

Usually, elastomers are processed through extrusion, forming in matrices, mixing. The first observations on the cold degradation of rubber by two roll-mixing, in the last century, refers to the fact that, under prolonged processing, natural rubber becomes sticky [703-705],... 

Natural rubber s processing by two roll-mixing, in the presence of styrene, at temperatures ranging within the 75-130 C interval permits a rapid polymerization of the monomer. The reaction is influenced by the elastomer/styrene weight ratio, being observed that its decrease causes increase of the polymerization reaction rate, which comes to exceed the one corresponding to styrene s thermal polymerization. 

In this manner, natural rubber modified with maleic anhydride was obtained, two roll-mixing being applied as the processing method [710],... 

Mechanochemical reactions during polymer processing by two roll-mixing... 

Thus, by chemical and spectral methods, the products resulted by the simultaneous two roll-mixing of PVC with benzidine, o- or / -PhDA were proved to contain aromatic rings on the main chain [301,308], By the photocolorimetric dosage of the unreacted diamine, the percentage of the diamine reacted with PVC (with respect to the initial amount) could be estimated. Figure 3.231. 

An important effect for the practical processing of PVC is noticed in case of its two roll-mixing in the presence of benzidine which could partially substitutes the classical thermal stabilizer... 

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