Formation of Agglomerates

Extruded products frequently contain additives in the form of powders ranging in concentration from less than 0.5 % pigment or antiblock to 40 or 50 wt% filler or flame retardant. With moves to reduce use of halogens, water-liberating flame retardants such as alumina trihydrate whose water of crystallisation is liberated at about 170 C, may be required at up to 50 wt% to meet specific fire retarding performances. There are attractions, either economic or technical (or both), in compoimding particulate blends of polymers with these additives during product extrusion. 

For pigments, antiblocking additives, and other additives required at low concentrations, the masterbatch route is normally technically the best and most reliable. It is also the best for minimising cleaning and facilitating automatic and accurate dosing. 

1) (There is) ... abundant evidence to show that agglomerates are normally produced under circumstances largely overlooked and unsuspected . 

2) (It is) ... largely true that once formed, an agglomerate stands a reasonable chance of never meeting conditions which break it down, the production of good quality dispersions is made difficult or impossible . 

3) Problems of agglomeration can be overcome simply by avoiding their formation . 

---

Formation of agglomerates by powder compaction may involve rearrangement of particles to increase their packing efficiency resulting in the enhancement of interparticle adhesion forces [89]. Furthermore, particle deformation at the point of contact between particles can greatly increase both the contact surface area and interparticle attraction [84]. 

The frequency of the linear CO is higher than that found for Pd films (j co = 2085 cm-1) (27) or for supported palladium (Pd/Si02), vco = 2060 cm-1) (28). The increase in frequency reported in this study is the result of the decrease of the backdonation from the d metal orbitals to the 7T orbital of CO. Y zeolites have very strong Lewis acid sites these sites should be able to decrease the electronic density of the palladium atoms bonded to CO. The decrease of the intensity of the band at 2100 cm-1 by increasing the hydrogen reduction temperature could be explained by the formation of agglomerates of palladium still in interaction with a Lewis acid site. 

Granulation by pelletizing involves preliminary formation of agglomerates from uniformly moistened particles or deposition of dry particles on moistened substance in the granulation centers. Such a process is attributable to th action of capillary adsorptive forces between particles and to subsequent compaction of the structure due to forces of interaction between the particles within the compact dynamic layer. 

Concerning the first step of coating, when the particles of polyolefin are introduced into the bed, their external surface becomes softer but their inside is cold, due to their low thermal conductivity. The softened surface is responsible for the formation of agglomerate made up of a plastic particle surrounded by sand particles. When the whole plastic particle... 

A related problem occurs during the fluidized-bed combustion of low-rank coals. The fluidized-bed combustion of high-sodium coals, particularly in silica beds, leads to the formation of agglomerates of ash and bed material. The agglomerates decrease heat transfer and fluidization quality of the bed in severe cases the formation of... 

---