Nonblack fillers

Nonblack fillers such as the precipitated siHcas can reduce both rate and state of cure. The mechanism appears to be one of a competitive reaction between mbber and filler for the zinc oxide activator. Use of materials such as diethylene glycol or triethanolamine prevents this competition thereby maintaining the desired cure characteristics. Neutral fillers such as calcium carbonate (whiting) and clays have Httie or no effect on the cure properties. 

Table 11. Effects of Nonblack Fillers in Natural Rubber ...

Silica is unique among nonblack fillers. Its reinforcing ability is comparable to that of carbon black, especially when mixed with a suitable coupling agent, and its transparency affords many products. Additionally, it is chemically synthesized, which means that a wide range of silica (in terms of diameter, surface area, or surface activity) may be produced depending on the reaction routes and reaction conditions. 

Filler Carbon black Natural amorphous silica, precipitated silica, nonblack nanofiller Solvent Organic solvent Aqua-based solvent... 

Non-benzenoid aromatic compounds, flash vacuum pyrolysis for, 21 148 Non-benzenoid quinones, 21 238 Nonbenzidine-based dyes, 9 448 Nonblack fillers, 21 781... 

Styrene-butadiene latex, 23 348 Styrene-butadiene rubber (SBR), 9 556-558, 23 325, 348 from butadiene, 4 384t colloidal suspensions, 7 275 effect of nonblack fillers on properties of, 21 783t... 

Light. Ultraviolet (uv) light promotes free-radical oxidation at the mbber surface which produces discoloration and a brittle film of oxidized mbber (35). This skin cracks in random directions to form a pattern called crazing, which can be prevented by the addition of carbon black fillers or uv stabilizers. Black stocks are more resistant to uv light than are gum or light-colored stocks. Nonblack compounds require larger quantities of nonstaining antioxidants which should bloom to the surface as the surface uv stabilizers deplete. 

Best compression set of nonblack fillers neutral filler good for colors poorer tensile strength than MT Black General-purpose mineral filler, neutral and good for control stocks tensile comparable with MT... 

Best compression set of nonblack fillers neutral filler good for colors poorer tensile strength than MT black. 

Nonblack fillers are used where colour or other properties are important. Some of the options are discussed next. 

Langford Clay. [R.T. Vanderbilt] Soft kaolin inert filler for elastomers, nonblack stocks. 

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. 

Nonblack Fillers. Because these are usually liquids, they are the one class of raw materials that most mixing shops today handle at least semiautomatically. For those plasticizers used in large quantities, bulk handling is advantageous. Preheating is usually necessary for some of these materials in order to reduce their viscosity for proper processing. 

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. 

Fig. 4. Reinforcing effect on hardness of nonblack fillers with different surface areas. < Silica, talc, calcium carbonate, x soft clay, hard clay.

For comparative purposes, the effects of nonblack fillers, both natural rubber and SBR compounds, are shown in Tables (12) and (13). For example it illustates... 

Surface Treatment. Carbon black remains the particulate filler of choice for rubber articles since the inherent reinforcing effect of the nonblack fillers in hydrocarbon elastomers is not comparable. This is primarily due to the nonbonded interactions established between the particulate filler and polymer functionality (28). Surface chemistry plays an important role in the interaction of the nonblack fillers and the polymer with contributions ranging from electrostatic interactions to covalent bonding to the polymer backbone. However, surface chemistry also strongly affects the interaction of the nonblack filler with other chemicals in the rubber compound, particularly active metal oxides, curatives, and antidegradants. 

---