Closed mixers

Figures 29.11 and 29.12 demonstrate the results of the silanization efficiency for different mixers and different fill factors under standard conditions (closed mixer) compared to working with an open mixer. The silanization efficiency is measured by viscosity and Payne effect.

The propellants used were some years agochloro-fluorocarbons (CFCs) (11 and 12) in various proportions (65 35 or 50 50). The manufacturing process includes the suspension formation in liquid propellant 11 in a cooled and hermetically closed mixer containing drug and lubricants. This mixture is introduced in the cans that are closed by a special powder valve, and propellant 12 was then injected through the valve. The upper part of the valve has often a special aperture through which a gaseous phase cleans the valve as well as the actuator. 

With a closed mixer, control of distributive mixing is inherently good, since all materials are added in a single batch and mixing occurs in two stages. Failure to add an ingredient or to improperly treat raw materials may lead to dispersion and homogeneity problems. 

Figure 17. Effect of processing time at 180°C on the peroxide and conjugated carbonyl concentration in polypropylene. (1) peroxide (open mixer) (2) peroxide (closed mixer) (3) conjugated carbonyl (open mixer) (4) conjugated carbonyl (closed mixer).

The dispersed elastomer particles are uncross-linked (TPE-O or TPO), but may also be cross-linked (TPE-V). The cross-linking (vulcanization) occurs during compounding in closed mixers (batchwise) or with twin-screw extruders (continuous). 

Discontinuous, batch wise processes in closed mixers (kneaders) and on mills and... 

The advantages of making up the mixture in a closed mixer (kneader) ... 

The high investment sums required for large closed mixer lines for making up mixtures from compact rubber bales led to the use of pulverized and crumped polymers in mixing extruders. 

To understand the mechanism of degradation of PET better, some samples (dry and humid) were processed in a closed mixer at two different rotational speeds. The Newtonian viscosity is plotted in Fig. 10 against the processing time. The degradation increases with time and with the rotational speed. Thermal degradation is then enhanced by the presence of the mechanical stress which acts as a catalyst of the thermal degradation. 

Fig. 3.14. The effect of processing temperature and time on hydroperoxide concentration in low density polyethylene. The numbers on the curves are processing temperatures (in °C) (C) indicates a closed mixer. (Reprinted with permission from [414], Pergamon Press Ltd, Oxford, England.)...

Figure 9.2 The effect of processing time on the extent of binding of polystyrene to polyethylene during processing in a closed mixer under N2 at 170°C. (1) PE/PS (1 1)+ 1 g/lOOg CHP, after methyl ethyl ketone extraction (2) PE/PS (1 1) +1 g/lOOg CHP, before extraction (3) PE/PVC (1 1) + 0.1 g/lOOg CHP, after extraction. From M. Hajian et al., Eur. Polym. J. (1984) 20, p.135-138...

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...

Figure 12 Comparison of effectiveness of different commercial UV stabilizers with oxidatively processed, under controlled conditions, polypropylene-containing sulfur antioxidants (DBDS + NiDBP + HOBP, referred to as COPS), and with the same system but processed mildly in a closed mixer (referred to as CM PS). Total concentration in each case is 0.4% ...

Figure 13 Effect of processing conditions on photooxidative stability of PE containing additives (1 x 10" mol 100g ) (1) control processed for 10 min in closed mixer (10, CM) (2) control processed for 10 min in open mixer (10, OM) (3) FeDMC (10, CM) (4) FeDMC (30, OM) (5) FeAcAc (10, CM) (6) FeAcAc (30, OM). Insert shows the effect of FeDMC and FeAcAc (2.5 x lO" mol 100 g" ) on the melt flow index (MFI) of PP processed in a closed mixer of a RAPRA torque...

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