Calcium carbonate processing aids

During production of factice, other additives may be employed to lower the cost or buffer the pH, or adjust the processability. Calcium carbonate, process oils, and magnesium oxide buffer are some of the items that are added at relatively low levels to modify factice. Certain proprietary process aids may be added to improve processing characteristics. 

As discussed in Chapter 10, a wide variety of additives is used in the polymer industry. Stabilizers, waxes, and processing aids reduce degradation of the polymer during processing and use. Dyes and pigments provide the many hues that we observe in synthetic fabrics and molded articles, such as household containers and toys. Functional additives, such as glass fibers, carbon black, and metakaolins can improve dimensional stability, modulus, conductivity, or electrical resistivity of the polymer. Fillers can reduce the cost of the final part by replacing expensive resins with inexpensive materials such as wood flour and calcium carbonate. The additives chosen will depend on the properties desired. 

A biodegradation accelerant increases or accelerates the rate of biodegradation in the environment. For example, calcium carbonate, calcium hydroxide, calcium oxide, barium oxide, barium hydroxide, sodium silicate, calcium phosphate, magnesium oxide, may accelerate the biodegradation process. These compounds may also act as processing aids. A commonly used compound is calcium carbonate (20). 

The primary particle size of Winnofil stearate coated precipitated calcium carbonate from Zeneca Resins is in the region of 0.075 micron. When compounded into natural and synthetic elastomers, the hydrophobic surface coating assists wetting and aids dispersion. When compounded into plasticised PVC for cable sheathing, the PCC allows for formulations with minimal potential for acid gas release in combustion conditions. In rigid PVC, stearate coated PCC has been used in compounding as an alternative to conventional acrylic processing aids and as a means to reduce impact modifier levels. 

Filtration is the most straightforward, probably the oldest form of sugar liquor clarification process. Filtration is effected with plate and frame pressure-filters or some type of leaf pressure-filter such as Sweetland filters with stationary suspended circular leaves covered on both sides with filter cloth. A filter aid of some sort (diatomaceous earth, paper pulp, or kieselghur) is essential to the operation. The precipitated calcium carbonate serves as a filter aid in the carbonation process. The liquor is mixed with the filter aid and forced under pump pressure through the fabric, which retains the cake and allows the clear liquor to flow through. The retained sugar in the cake can be washed out with hot water. Filtration is no longer used as the sole means of clarification. The process is used for further clarification of the liquor from a carbonation or phosphatation process. 

Distinguishing between calcium carbonate precipitates adjacent to actively metabolizing cyanobacteria versus cell directed mineralization, i.e., via bioorganic molecular templates, is often moot. It is probable that both processes take place intermittently if not sequentially with shifts in temperature and composition, alkalinity or salinity, of the surrounding fluid media, especially when the waters are effectively saturated with respect to carbonate and calcium ions. Where the waters are in rapid motion, as in springs and waterfalls, CaCOs deposition may be aided by evaporation while bioprecipitation of carbonates is also taking place (Golubic, 1973, 1983). 

WfamofiL pClResins] Precipitated stearate-coat calcium carbonate filler, impact modifier, processing aid for theinKq>lastics and pauns. 

WinnofiL [ICI Resins] Precipitated stearate-coated calcium carbonate filler, inquict modifier, processing aid for tham(q>lastics and patnis. 

The extract contains, in addition to the sucrose, further solved or colloidally dispersed components, which in the juice purification stage must be - as far as possible - precipitated or destroyed under alkaline conditions by adding calcium oxide. This is carried out by a multi-stage, continuous treatment with, first, calcium oxide and, second, carbon dioxide. Both processing aids are produced in a separate calcining process in parallel. The excess calcium oxide is precipitated in so-called carbonation vessels with carbon dioxide from the calcining process. All precipitates and deposits are separated in a multi-step filtration. The sludge... 

Reinforcing fillers used are carbon black and non-black fillers such as silica, clay, and calcium carbonate although the latter two are used more in lower cost industrial applications and not in tires. Protectant systems consist of antioxidants, antiozo-nants, and waxes. The vulcanization system essentially ensures that the optimum mechanical properties of the polymer system are achieved. Finally, the tire compound can contain various miscellaneous materials such as processing aids and resins. The materials scientist when designing a tire compound formulation has a range of objectives and restrictions within which to operate. Product performance objectives define the initial selection of materials. These materials must not raise environmental concerns, be processable in tire production plants, and be cost effective for the end user [4]. 

Other substances used include MBS polymers and various functionalised polymers. Calcium carbonate can act as a process aid in film blowing, increasing the strength and stiffness of the product and improving output. 

Additives with specific functions (such as flame retardants, anti-statics, and conductives) are now also expected to make a contribution to facilitating processability. Traditional fillers, such as calcium carbonates, are surface modified to give them additional value and, at the other end of the spectrum, highly sophisticated polymers such as fluoroplastics are being modified to play key roles as processing aids. 

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