Starved feed operation

The variation of copolymer composition during the course of a batch polymerization can be reduced by conducting the reaction as a so-called semibatch process. This is a starved feed operation in which part of the charge is fed to the reaction vessel and polymerization is started. The remainder of the monomer feed is pumped in continuously or intermittently at a rate sufficient to keep the... 

For extrusion compounding, if the components have different densities (e.g. polymer versus fillers) or different shapes (pellets versus regrind flakes) then prefer to use the extruder for mixing. That is, operate the extruder with starved feeding conditions with the components metered separately into the extruder, see Section 9.11. On the other hand, for the blending of polymer feedstock for extrusion, if the components have very similar properties, then use tumble, rotating drum or ribbon blenders or rotor-stator blenders of the feed upstream of the extruder and use flood feeding of the mixture to the extruder. 

Always operated by starve feeding, flood feeding not possible... 

Although rotor-stator mixers can pump to some extent, it is preferred to use a pump to control the feed rate to the mixer. This way, one does not need to vary the rotor speed to control the flow rate. Instead, the rotor speed can be varied to control the energy input, turbulent kinetic energy, and shear rates in the device, independent of the flow rate. To prevent equipment failure, it is also important to ensure that the unit is fully flooded and not starved during operation. 

LDPE (135 °C). The results indicate that the solids conveying zone is operating properly and that higher outputs could be obtained before the solid bed no longer fills the channel. The condition in which the channel is only partially full is referred to as starve feeding and is dealt with in Problem 8B.4. The power input through the barrel is obtained from Eq. 8.29 and is... 

Intoxicating chemicals are those that are not necessarily lethal (see Pesticides) but operate as primary repellents or secondary repellents, eg, emetics causing sickness or distress. Primary bird repellents are those whose mode of action is having a bad taste immediate rejection of food is the desired result. However, they are effective only if other foods are available they are not effective in times of food shortages, because large flocks of migrating birds would be forced to feed or starve. Bird repellents have been discussed in reviews (51,56). 

Regulation of contact sex pheromone production in B. germanica operates at several levels, including (i) production of the 3,11-dimethylnonacosane precursor, (ii) its metabolism by female-specific oxidases to 3,ll-dimethylnonacosan-2-one, and (iii) transport and distribution of the pheromone to the epicuticular surface. Early in the life of an adult female, it appears that food intake is a major regulator of hydrocarbon production. Females produce hydrocarbons only when they feed, and experimentally starved females, or gravid females that feed less, produce significantly less hydrocarbon (Schal el al., 1994). Because a pool of precursor 3,11-dimethylnonacosane is required for pheromone to be made, little pheromone is produced when less hydrocarbon is available, for example in starved females. 

Likewise, for the semibatch operation, the influence of monomer was seen in the differences between macro- and miniemulsion feeds. For extremely water-insoluble monomers, the miniemulsion-feed mode lessens the departure of the copolymer composition from the feed composition during semi-starved semibatch polymerization. However, this is accomplished by simultaneously broadening the PSD. Results from the GPC analysis indicated that the polymers with lower molecular weight and broader distribution were formed in the semibatch process, in contrast to the batch run. 

A second motivation for using a monomer-feed semibatch procedure is to control copolymer composition and/or particle morphology. Delayed feed of part of the more reactive monomer can be used to eliminate or reduce the composition drift of the copolymer. The delayed feed of a comonomer mixture when the reactor is operated in the monomer-starved regime can also be used to prevent copolymer composition drift. Such operations will produce polymer particles with more uniform morphology. Different monomer addition schemes can be employed to control nonuniform particle morphology (see papers by Bassett et al. in General References 7 and 9). 

The feed zone is the area where the moistened formulation is first introduced into the extrusion device. It includes a hopper to channel and distribute the flow of material into the chamber containing the screw(s). Most screw extruders will be operated with only a slight excess of feed or even in a somewhat starved state. Because, for extrusion, the material must be plastic, too much feed tends to build up over the screws and bridging is likely to occur. 

The flrst point is a reasonable assumption provided there is a disjunctive categorization of locations into material (net) providers and (net) consumers such that there is one unique flow direction within the pipeline, i.e. Xj > 0 or X/ < 0 for all locations j. I.e. if the pipehne is serially operated, the total safety stock has to be distributed among the provider locations. Another situation occurs for cyclic pipehnes. Here, the material flow is unidirectional, but each location can act as consumer or provider as long as the total flow is balanced. The safety stock can be distributed among all participants along the pipehne as long as all participants can feed surplus material from stock to starving partners. 

It is important to ensure that the maximum feed rate from the storage bin is always greater than the maximum expected operating rate of the feeder. Otherwise, the feeder will become starved and flow-rate control will be lost. This problem is particularly pronounced when handling fine powders because their maximum flow rate through an opening is significantly less than that of coarser-particle bulk solids whenever a mass-flow pattern is used [1]. 

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