Zinc oxide viscosity

Cure Characteristics. Methods of natural rubber production and raw material properties vary from factory to factory and area to area. Consequentiy, the cure characteristics of natural mbber can vary, even within a particular grade. Factors such as maturation, method and pH of coagulation, preservatives, dry mbber content and viscosity-stabilizing agents, eg, hydroxylamine-neutral sulfate, influence the cure characteristics of natural mbber. Therefore the consistency of cure for different grades of mbber is determined from compounds mixed to the ACSl formulation (27). The ACSl formulation is as follows natural mbber, 100 stearic acid, 0.5 zinc oxide, 6.0 sulfur, 3.5 and 2-mercaptobenzothiazole (MBT), 0.5. 

In addition to suspensions, pharmaceutical products may be emulsions or foams. In any case the rheological properties have to be tailored to suit the nature of the application [215], Therapeutic ointments are usually not very viscous and encounter only moderate shear rates upon application, about 125 s-1 when gently smeared on with fingers, and about 210 s-1 when smeared on with a spatula [215], An opthalmic ointment is usually very soft, with a viscosity of about 20-30 mPas, whereas a medicated ointment needs to be soft enough to apply easily but stiff enough to remain on the area to which it was applied, with a viscosity of about 30-40 mPas [215], A protective ointment like zinc oxide paste needs to be hard and stiff enough to stay in place where applied, even when moist. 

Mineral oil—a mixture of liquid hydrocarbons obtained from petroleum. These are useful as levigating agents to wet and incorporate solid substances (e.g., salicylic acid, zinc oxide) into the preparation of ointments that consist of oleaginous bases as their vehicle. There are two types of mineral oils listed in the US. Pharmacopeia/National Formulary (USP/NF). Mineral oil USP is also called heavy mineral oil with a specific gravity between 0.845 and 0.905 and a viscosity of not less 34.5 cSt (cSt = mm /s) at 40°C. Light mineral oil, NF has a specific gravity between 0.818 and 0.880 and a viscosity of not more than 33.5 cSt. Table 2 lists the commercially available mineral oil fractions. 

Generally, most asphalt is 79-88% w/w carbon, 7-13% w/w hydrogen, trace-8% w/w sulfur, 2-8% w/w oxygen, and trace-3% w/w nitrogen.Trace metals such as iron, nickel, vanadium, calcium, titanium, magnesium, sodium, cobalt, copper, tin, and zinc occur in crude oils. Vanadium and nickel are bound in organic complexes and, by virtue of the concentration (distillation) process by which asphalt is manufactured, are also found in asphalt. The catalytic behavior of vanadium has prompted studies of the relation between vanadium content and an asphalt s sensitivity to oxidation (viscosity ratio).The significance of metals in the behavior of asphalts is not yet well understood or defined. 

This chapter describes ionic cross-linldng of the HASE thickener with zinc oxide or zinc ammonium complexes to improve early blister resistance. Zinc ammonium complexes have been used in ammonia-removable latex floor polishes for decades. Paint formulations containing zinc oxide have benefits but are prone to sporadic viscosity instability, which sometimes cannot be predicted by standard laboratory tests. However, many paint manufacturers have learned how to successfully stabilize these zinc oxide-containing latex paints. 

Paint Stability. Table III shows that paints containing the higher levels of zinc oxide had a greater viscosity drop after heat aging, and gelled after three freeze-thaw cycles. At 0.5 eq of zinc per COOH unit, both the zinc oxide and zinc ammonium carbonate paints were stable. 

Table IV shows that paints containing the higher levels of zinc ammonium complexes also generally showed the greatest viscosity drop on heat aging. Table IV also shows that these paints had poorer freeze-thaw stability. Close attention to formulation techniques, such as the judicious choice of dispersants and surfactants, can minimize or eliminate this problem in zinc oxide-containing latex paints.

Table III. Viscosity Stability of Zinc Oxide-Modified Paints with HASE Thickener...

Compound PI Blend of two EPDM copolymers, one with high ethylene content and medium Mooney viscosity, the other with medium ethylene content and low Mooney viscosity. Contains carbon black, zinc oxide, TMQ, paraffinic process oil, dicumyl peroxide and a sulphur donor. 

It is very important to mention that at ambient temperature carbamate groups tend to hydrolyze under alkaline conditions more easily. Therefore, solutions of cellulose carbamate must be chilled off [3]. Struszczyk [82,83] demonstrated that such solutions are stable below 0°C. All commercial processes, namely dissolution of cellulose carbamate and solution storage must be handled at low temperatures to avoid changes in viscosity. Some additives also can be used to control the solution s viscosity and to reduce gelation. The addition of 1-3% zinc oxide to a spinning dope tends to increase the viscosities of these solutions and improves the spinnability [3]. This additive also extends the solution s storage life. 

To obtain high molecular weights by this method, almost complete removal of the phenol is required. The reaction is carried out with typical basic catalysts, like lithium hydride, zinc oxide, or antimony oxide under an inert atmosphere. The initial reaction temperature is 150 C. It is raised over a one-hour period to 210 °C while the pressure is reduced to 20 mm Hg. The reaction mixture is then heated to about 300 °C for 5-6 hours at 1 mm Hg. Heating is stopped when the desired viscosity is reached. 

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