Internal Mixing Procedures

If possible, single pass, upside-down mixing is preferred to control overheating. Upside-down mixing allows the fillers and additives to be blended by the rotor without any temperature increase. The polymer is added last maximizing the time of mixing. Table 6.20 outlines the recommended internal mixing procedure for AEM compounds. 

Mixing. Ethylene—acrylic elastomers are processed in the same manner as other elastomers. An internal mixer is used for large-scale production and a mbber mill for smaller scales. In either case, it is important to keep the compound as cool as possible and to avoid overmixing. Ethylene—acryflc elastomers require no breakdown period prior to addition of ingredients. Mixing cycles for a one-pass mix are short, typically 2.5—3.5 min. When compounds are mixed on a mbber mill, care should be taken to add the processing aids as soon as possible, after the polymer has been banded on the mill. Normal mill mixing procedures are followed otherwise. 

To use KBr discs for quantitative measurements it is best to employ an internal standard procedure in which a substance possessing a prominent isolated infrared absorption band is mixed with the potassium bromide. The substance most commonly used is potassium thiocyanate, KSCN, which is intimately mixed and ground to give a uniform concentration, usually 0.1-0.2 per cent, in the potassium bromide. A KBr/KSCN disc will give a characteristic absorption band at 2125 cm 1. Before quantitative measurements can be carried out it is necessary to prepare a calibration curve from a series of standards made using different amounts of the pure organic compound with the KBr/KSCN. A practical application of this is given in Section 19.9. 

The compounds were mixed in three steps The first two steps were done in an internal mixer with a mixing chamber volume of 390 mL. The mixing procedures employed in the first two steps are indicated in Table 29.2. The starting temperamre was 50°C and the cooling water was kept at a constant temperature of 50°C. The rotor speed was 100 rpm and the fill factor 66%. After every mixing step the compound was sheeted out on a 100-mL two-roll mill. The third mixing step was done on the same two-roll mill. The accelerators and sulfur were added during this step. 

Despite the successes of these chemical procedures, they are still fraught with difficulties in terms of the predictability of the properties of the final products. Thus, except in a very few cases, it is impossible to predict conditions that would yield particles of a given shape. Even obtaining a desired particle size by a chemical process that can produce a monodisperse system must be established experimentally. When dealing with finely dispersed matter of internally mixed composition additional problems are encountered, because the molar ratio of constituents in the solid phase usually differs from those in solutions in which the precipitates are formed (4,5). 

ISSA TB-113. 1990. Trial mix procedure for slurry seal design. Annapolis, MD International Slurry Seal Association. 

It is necessary for the development of suitable methods of product fabrication to have some types of polyurethane elastomer which can be processed as solids using similar methods to those employed for conventional natural and synthetic rubbers, namely two-roll mill or internal mixing and compounding procedures, calendering, extrusion, moulding, fabrication of complex rubber-textile laminates and the like. 

The widespread nse of internal mixers for polymer compounding over many decades, has resulted in many refinements to mixer, and particnlarly rotor design, together with optimisation of mixing procedures. 

Clean fuel and good mixing procedures are a must. I ve found that a five-gallon, plastic container with an internal, fine-screen spout and capped vent is the best. Metal containers tend to generate water from condensation and rust when not kepi completely full. 

Polyepichlorohydrin compounds can be mixed either on a mill or in an internal mixer. The mixing procedure for either method is virtually the same as for SBR, NBR, and EPDM compounds. Because of shelf-Ufe concerns, a two-pass mix may be preferable. 

Mixing in an internal mixer is best, but open mill mixing may also be satisfactory. An upside down mixing procedure is best with internal mixers. 

Figure 11 Effect of mixing procedure (processing under mild conditions, closed mixer (CM) and under oxidative conditions, open mixer (OM) of an internal mixer, a RAPRA torque rheometer) on photooxidative stability of PP containing additives (2.5 X 10mol 100g ). Inset compares photostabilizing effectiveness of mildly processed (CM) thiophosphoryl disulfide...

Procedure. A vitamin B complex tablet Is crushed and placed In a beaker with 20.00 mL of a 50% v/v methanol solution that Is 20 mM In sodium tetraborate and contains 100.0 ppm of o-ethoxybenzamIde. After mixing for 2 min to ensure that the B vitamins are dissolved, a 5.00-mL portion Is passed through a 0.45- xm filter to remove Insoluble binders. An approximately 4-nL sample Is loaded Into a 50- xm Internal diameter capillary column. For CZE the capillary column contains a 20 mM pH 9 sodium tetraborate/sodlum dIhydrogen phosphate buffer. For MEKC the buffer Is also 150 mM In sodium dodecylsulfate. A 40-kV/m electric field Is used to effect both the CZE and MEKC separations. 

A solvent-free synthesis of flavones was recently reported by microwave-assisted reaction of phloroglucinol 231 and differently substituted /1-ketoesters 232 [148]. The reaction was simply carried out by mixing the phenol and the ester in an open test tube followed by irradiation for 2-3 min. The internal temperature reached 240 °C and yields were in the range from 68 to 96%. Scheme 85 describes the application of this procedure to the synthesis of the natural product chrysin 233. 

---