Fine talc

Requirements for safe storage of powdered Al, Hf, Mg, Ti, Zn and Zr are outlined. Fires are best extinguished with various fluxes, trimethyl boroxine, asbestos fines ( ), talc, graphite, sodium chloride, soda ash, lithium chloride or powdered dolomite [ ] Slurries of Al, Cd, Cu, Ge, In, Ni, Pb, Sn or Zn produced by metal atom-solvent cocondensation at — 196°C are extremely active chemically [2], and would be pyrophoric on exposure to air. 

Talcs are either platy or acicular in particle shape. Thin platelet particles have aspect ratios varying from 20 1 to 5 1. Coarse particle sizes (10 to 75 im) are commonly used in these applications at loading levels of 5 to 30 percent. Fine talcs (1 to 10 im) are more expensive and require intensive dispersion processes. Platy grades enhance barrier properties and air, water, and chemical resistance. 

Hydrous magnesium silicate, is an industrial talc. It is available in four grades, two fine talcs and two ultrafine air milled grades with excellent white color. 

Talc occurs naturally and is mined, therefore the mineral composition may vary depending on the source [IS]. The most frequent impurities are alumina, calcium oxide, and iron oxide [4], The mined material is pulverized, and the talc is separated from impurities using a floatation process [16]. The fine talc is boiled in dilute hydrochloric acid to remove iron and other soluble impurities. It is then washed with water and dried. 

The process of formation of the crystalline state is controlled by the kinetics of nucleation and this may arise in a number of ways. Primary nucleation in a quiescent state must be associated with foreign bodies such as deliberately added nucleating agents, such as fine talc particles, or residual impurities such as heterogeneous catalyst particles followed by spherulite growth. The plot of extent of crystallinity, (p, as a function of time is sigmoidal in nature and follows an Avrami equation of the form... 

Talc is typically used at up to 50% loading, in particle sizes of 1-100 pm. "General purpose, coarse talcs (used in WPCs, for example) have particle sizes above 5 pm, while "fine talcs have median particle sizes between 2 and 4 pm and are particularly important for high-impact automotive TPO applications. In recent years, manufacturers have offered processing options for some... 

Table 7.1 Comparison of Mechanical Property Effects of Very Fine Talc in PE and PP (Luzenac and Jetfine 2-pm Median Size Talc from Rio Tinto)...

CASE 8.2 FINE TALC ALLOWS THINNER PE PACKAGING [8-10]... 

In thick, high-volume PO applications such as extruded pipe, standard (20-pm) talcs provide effective stiffness. But finer talc grades may allow reduced resin use by allowing thinner parts with equivalent beam stiffness. Reduced talc particle sizes (near 1 pm), for instance, can create a better balance of properties in thinner parts to help justify increased filler cost that results from the use of very fine talcs. Lower talc loadings may also be possible the newest high-aspect-ratio talcs are said to create the same mechanical properties at 3%-7% loadings in PP than in PP compounds loaded with 20% standard talc. Cases 8.1 and 8.2 cover applications in which different talcs supply these different functional needs [7-10]. 

Nucleation Fine talc Rio Tinto Luzenac and Jetfine PP Increased stiffness and crystallization temperature (short cycle times)... 

The monograph Sieves of the Ph. Eur. has a table with sizes and tolerances of a series of 18 sieves. The smallest sieve has (square) holes with sides of 38 pm, the largest holes with sides of 11.2 mm. The result of a sieve analysis is indicated as the percentage by weight of the substance that passes the sieve. Many raw materials are naturally fine (talc, starch) or will be delivered in the required degree of fineness, such as paracetamol (45) and salicylic acid (90). 

In other instances, the filler may nucleate crystal growth. This is often beneficial, as it causes the material to harden more rapidly on cooling, giving the possibility of faster production. In fact, it is common practice to add a small amount of fine talc to nucleate... 

Yua Sheng et al. [153] and Leong et al. [155] measured the tensile, flexural, and impact properties of ultra-fine-talc-filled polypropylene composites. Experimental results indicated that the addition of talc inflnenced the crystallization, morphology, and mechanical properties of talc-polypropylene composites. When the talc content was increased from 0% to 25%, the crystallinity of the polypropylene phase reached a maximnm at 15% talc and the tensile and flexural strengths of talc-polypropylene composites also attained a maximum, while the impact strength declined to its lowest level. Scanning electron microscopy photographs of impact... 

Traditionally, pitch problems were chemically controlled by the adsorption and dispersion of pitch particles by adding fine talc, dispersants, and other chemicals. However, this use of chemicals leads to problems with effluent treatment and environmental pollution. Seasoning of the wood before pulping is another method where the wood is left outdoors for several months. However, these affect the pulp s brightness and yield, which results in an increase in capital cost and land use. Enzymatic control has proven to be a successful alternative, where lipases have shown their ability to reduce the triglyceride content (Farrell et al., 1997). Lipase AYL, produced from C. rugosa and from C. cylindracea, has been successfully used in the pulp and paper industry (Singh and Mukhopadhyay, 2011). 

Using the Jenike concept of the ratio of maximum compaction stress to an unconflned stress - flow function jf- Stanley-Wood and Abdelkarim (1982) and Abdelkarim (1982) superimposed the experimental parameters of unconfined and maximum compaction stresses, for a range of industrial powders (liquorice, chalk 2, fine talc, chalk 1 and di-calcium phosphate (DCP)) classed as either free flowing/non-cohesive, intermediate flowability or cohesive, onto the various degrees of cohesiveness postulated by the Jenike flow function, as outlined in Bulletin 123 (Figure 1.5). 

J. Qian, Preparation of wood-like mold composite material by premixing bamboo fiber, wood powder, low density polyethylene, polymer wax, thermoplastic plastic, ultra fine talc powder, styrene and methyl acrylate mixed monomer, and plastics. Changshu Fangta Coating Chem Co Ltd (2012). 

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