Curative sulfur compound

ATM— factice contains between 0.3% and 4.0% free sulfur. This needs to be recognized as a significant increase of curative in a sulfur compound. In a peroxide cure situation, only low levels (<10 phr) of sulfur factice can be tolerated unless a sulfurless grade is used (TDI cross-linked castor type). 

The productive stock, ie, the curable compound, is made up by mixing the nonproductive stock in the Banbury once more with the curative package (sulfur, accelerators, etc). This time the drop temperature is lower, in the range of 95—112°C. The productive stock is then sheeted or pelletized and coated with the dip coat, cooled, and finally stored, ready for further processing for final fabrication. 

Fig. 32 WAXD patterns of NBR compounds reinforced with 5 phr organoclay and cured by sulfur (a), peroxide (b), and NBR master batch (c) (without curatives and uncrosslinked)...

The SEM is also used to do X-ray/elemental analysis. This technique is qualitative. X-ray analysis and mapping of the particular elements present is useful for the identification of inorganic fillers and their dispersion in compounds as well as inorganic impurities in gels or on surfaces and curatives, e.g., aluminum, silicon, or sulfur in rubber compounds and Cl and Br in halobutyl blends. (Figure 9)... 

Polymers were compounded on a cold 3x10 inch laboratory mill using the following recipe (in parts) gum 100, stearic acid 1, ZnO 5, tetramethylthiuram disulfide 1, ALTAX 1, sulfur 1.75 and PBNA 0.5. All curatives were used as supplied without further purification. The compound became homogeneous after about forty minutes of milling. More time was required when carbon black was used. The compound was sheeted and cured in a 0.0625 inch thick mold at l Xf for 30 min. 

In this respect, it is important to note the conclusions reached by Westlinning99 who compared the abrasion resistance at the same modulus of two series of compounds, one in which the modulus was obtained by the use of sulfur and curatives, the other by the addition of carbon black to a single basic compound. He found that while the abrasion resistance of the latter increased up to a certain maximum, the resistance of the former fell continuously and rapidly. Also, abrasion resistance is... 

A large number of investigations in acid media have led to the conclusion that the inhibition effect caused by relatively small and simple molecules is due to their adsorption on the metal surface. Compounds of this nature usually contain sulfur and nitrogen, or are of the groups of higher alkyl-alcohols and fatty acids. Typical compounds to be discussed here in more detail are quinoline and thiourea derivatives. Fig. 5 shows a comparison of the effectiveness of several such compounds determined by means of weight loss measurements on carbon steel in 5% sulfuric acid at 40° C. as a function of the inhibitor concentration. A cur-... 

Filler dispersion is a property that determines how well the filler partciles in a given rubber compound are dispersed as a result of the mixing process. This relates to carbon black dispersion as well as the dispersion of nonblack fillers such as silica, clay, calcium carbonate, titanium dioxide, etc. Also rubber curatives such as sulfur and accelerators can be poorly dispersed (commonly these ingredients are added late in the mixing cycle). Poor dispersion makes a mixed stock less uniform, and commonly the cured ultimate tensile strength will have more variability. Poor dispersion can affect other important cured physical properties such as abrasion, tear, and fatigue resistance, flexometer heat buildup, and other dynamic properties. 

In SBR the compounding ingredients can be (1) reinforcing fillers, such as carbon black and silica, which improve tensile strength or tear strength (2) inert fillers and pigments, such as clay, talc, and calcium carbonate, which make the polymer easier to mold or extrude and also lower the cost (3) plasticizers and extenders, such as mineral oils, fatty acids, and esters (4) antioxidants, basically amines or phenols, which stop the chain propagation in oxidation and (5) curatives, such as sulfur for unsaturated polymers and peroxides for saturated polymers, which are essential to form the network of cross-links that ensure elasticity rather than flow. 

Most molecules are at peace with themselves. Bottles of sulfuric acid, sodium hydroxide, water, or acetone can be safely stored in a laboratory cupboard for years without any change in the chemical composition of the molecules inside. Yet if these compounds are mixed, chemical reactions, In some cases vigorous ones, will occur. This chapter is an introduction to the behaviour of organic molecules why some react together and some don t, and how to understand reactivity in terms of charges, orbitals, and the movement of electrons. We shall also be introducing a device for representing the detailed movement of electrons—the mechanism of the reaction—called the curly arrow. 

The term refers to any chemical substance added to a plastic or elastomer compound to impart or improve certain end-use properties. Common additives are foam agents, colorants, curatives like sulfur or peroxide, accelerators, activators, tackiness agent, stabilizer packages, carbon black, clay. Refer to Carbon Black, Antizonanty and Antioxidants. 

The distribution of soluble compounding ingredients, especially curatives, may significantly infiuence the performance of the vulcanized product. Diffusion of common vulcanizing ingredients, such as sulfur, tetramethylthiuram disulfide (TMTD), benzothiazole disulfide (MBTS), and diphenylguanidine (DPG) occurs... 

Zinc oxide, which is formed from the burning of zinc metal, was the first nonblack filler nsed for reinforcement of rubber compounds. Although zinc oxide and magnesinm oxide are still used as reinforcing fillers in some specialty compoimds, particnlarly those that reqnire heat resistance, their role in rubber compoimding in the last several decades is that of an activator for the sulfur cure system or as curatives for chloroprene rubber compounds. 

The art of compounding (110) rises to the fore in the development of polymeric materials. Thus, fillers can be either reinforcing or inert and low price, or serve as pigments. Plasticizers and lubricants need to be added on occasion. Antioxidants and ultraviolet light absorbers lengthen the life of many polymers. Curatives such as sulfur for vulcanization or peroxides reduce flow, producing cross-linking. 

Sulfur crosslinks are thermally not as stable as some other types of crosslinks formed from the use of either peroxide or resin curatives. Sometimes these more expensive curative packages have to be used in place of sulfur-based systems to achieve the higher temperature resistance or better compression set resistance properties for the rubber compound. 

Polymer compounds often contain curatives or crosslinking agents. This is especially true for rubber compounds. The most important curatives are sulfur and sulfur compoimds. Elementary sulfur exists in a number of aUotropic forms [ 55 ]. Ordinary sulfur is a yellow solid substance, which forms crystals with orthorhombic symmetry. It is called orthorhombic (or rhombic, a-) sulfur. At 112.8 °C orthorhombic sulfur melts to form a straw-colored liquid, which consists of staggered ring Sg molecules and has a low viscosity. If this melt is cooled down, it crystallizes into a second polymorphic form monoclinic sulfur (y-sulfur). Orthorhombic sulfur (a-sulfur) is the most stable form at low temperatures, but above 95.5 C the most stable form is monoclinic sulfur (P-sulfur), which is stable between 94.5 and 120 C. This melts at 120 °C to form an Sg straw-colored melt. When molten sulfur is heated, it becomes more viscous because of its polymerization. It becomes darker in color and turns red. 

Curatives are introduced into compounds to crosslink polymer chains. The most important curative is sulfur which produces (polymer)-S -(polymer) crosslinks. This primarily involves unsaturated elastomers based on isoprene and butadiene such as natural rubber, polybutadiene, and its copolymers with styrene and acrylonitrile (see Section 1.3). After crosslinking, the polymer networks show increased retractive force and reduced creep. The cured rubber becomes insoluble and it cannot be processed in the molten state. The concentration of curatives and their reactivity affect the degree of crosshnking. 

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