Nucleating agent modification

Carbon black is also used as a pigment for paints and printing inks, as a nucleation agent in weather modifications, and as a solar energy absorber. About 70% of the worlds consumption of carbon black is used in the production of tires and tire products. Approximately 20% goes into other products such as footwear, belts, hoses, etc. and the rest is used in such items as paints, printing ink, etc. The world capacity of carbon black was approximately 17 billion pounds in 1998. U.S. projected consumption for the year 2003 is approximately 3.9 billion pounds. 

Among the three known crystalline structures (a, j3, y) of isotactic polypropylene (PP), the -modification is certainly the most fascinating one. While the stable a-structure develops under standard process conditions, the occurrence of the /J-form has to be forced (i) by directional crystallization in a temperature gradient field [1-3] (ii) by shear-induced crystallization [4-12] or (iii) by the addition of specific nucleating agents [13-31]. This latter technique is preferred at the industrial scale. 

Under standard processing conditions, PP crystallizes in between 5 and nearly 100% in the -modification depending on the nature of the -nucleating agent [13-31,126,127]. Industrially, only highly selective -promoters are of interest since the toughness is positively correlated with the -content in a more or less straightforward way (see Sect. 3.2.2). 

The combined modification of PP with fillers and /1-nucleating agents has been seen as attractive for its potential to achieve a breakthrough in the somewhat frozen stiffness/impact balance of PP. It has been speculated that the... 

Under defined conditions, the toughness is also driven by the content and spatial distribution of the -nucleating agent. The increase in fracture resistance is more pronounced in PP homopolymers than in random or rubber-modified copolymers. In the case of sequential copolymers, the molecular architecture inhibits a maximization of the amount of the /1-phase in heterophasic systems, the rubber phase mainly controls the fracture behavior. The performance of -nucleated grades has been explained in terms of smaller spherulitic size, lower packing density and favorable lamellar arrangement of the /3-modification (towards the cross-hatched structure of the non-nucleated resin) which induce a higher mobility of both crystalline and amorphous phases. 

D. A., ed., Environmental Impacts of Nucleating Agents Used in Weather Modification Programs." 270 p. Dowder, Hutchinson Ross, Stroudsberg, Pennsylvania, 1978. 

Jenne, E. A., Girvin, D. C., Ball, J. W., and Burchard, J. M. Inorganic speciation of silver in natural waters - fresh to marine. Chapter 4, p. 41-61, Klein, D. A., ed., "Environmental Impacts of Nucleating Agents Used in Weather Modification Programs," 256 p. Dowder, Hutchinson and Ross, Stroudsberg, Pa. 1978. 

Dehydrated calcium pimelate is added (between 0.01 and 0.5 wt %) as the nucleating agent to isotactic polypropylene to produce the (3 modification of iPP [63]. Following molding between two glass plates at 220°C thin films of the polymer are isothermally crystallized at 140°C-143°C in a microscopy hot stage. After the hedritic structures develop, the samples are quenched to room temperature. Prior to AFM examination, the specimens are etched with a 1% solution of potassium permanganate in a mixture of sulfuric and orthophosphoric acid [64, 65]. This procedure is described in detail in the literature Caution consult the literature for safety precautions ) and helps to remove preferentially amorphous phase of PP [64]. Thus, unlike in the many other examples discussed in Sect. 3.2, here the interior of a specimen is analyzed after its exposure. 

Takahashi, T. (2002). Crystal modification in polypropylene fibers containing P-form nucleating agent. Sen Gakkaishi, Vol.58, No. 10, pp.357-364. 

The parallel research conducted at our laboratory by DSC, PLM, and SEM [7] techniques were to explain why the chemical modification with agents promoting adhesion decreases the nucleation activity of hexagonal form crystallization... 

Graphene at low concentrations (below 1 wt%) is a nucleating agent of polycarbonate." Graphene with surface modification reinforces PC." Also, sihca was foimd to nucleate PC. ... 

The fraction of p-ciystal modification in polypropylene is increased to above 50% by addition of iron oxide."" Nanoscale magnetite and nanoscale maghemite are proven to be particularly effective 3-nucleating agents in polypropylene."" They are added in quantity of 1-3 wt%.""... 

Depending on the ciystallization conditions, sPS chains can ciystalUze into at least four ciystalline modifications (a, p, y, and 8 forms). The mechanical strength of sPS samples depends on the crystalline modification and the degree of ciystalUnity. Graphene nanosheets acted as P-nucleating agent for syndiotactic polystyrene. Carbon nanotubes increase peak crystallization temperature by 14°C. ... 

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