The Polyvinyl Alcohol and Vinyl Acetate

Polyvinyl alcohol is a kind of can't directly through the polymerization of the monomers and polymers, because vinyl alcohol monomer is not exist alone, it is very unstable, under normal circumstances will spontaneously by intermolecular rearrangement into acetaldehyde, so can not use vinyl monomer polymerization of polyvinyl alcohol. The general method of polyvinyl alcohol preparation: first with vinyl acetate monomer by polymerization of poly vinyl acetate, and then poly vinyl acetate alcoholysis and hydrolysis of polyvinyl alcohol.

Vinyl acetate monomer for preparing poly vinyl acetate is solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization of four methods.

Bulk polymerization has the advantages of high purity, production fast, short process flow, simple process, but because no heat medium, along with the reaction, the viscosity of the system increases, the reaction heat to evaporate, easy to generate local overheating, the product color, even the implosion phenomenon, it is often used in a small amount of polymer laboratory studies of preparation, dynamical study. Solution polymerization method in the presence of solvents, chain transfer reaction is easy to happen, the low degree of polymerization, but its degree of polymerization and the molecular weight distribution is narrow, the products of good quality, and easy to heat dissipation, the industry generally by solution polymerization. Suspension polymerization is usually with water as medium, easy heat dissipation and temperature control, the degree of polymerization and the molecular weight is higher, but because of a small amount of residual suspension products, post treatment is complex, the cost of production. Emulsion polymerization with water as the dispersion medium, to facilitate heat dissipation and temperature control, and the polymerization rate, molecular quantity obtained high, but because the polymerized emulsion by condensation, washing, dehydration, drying after processing, the production cost is suspended high.

Vinyl acetate polymerization reaction is exothermic reaction (89.2KJ/mol), remove the reaction heat and the reaction was carried out with difficulty;, viscosity of polymerization system increases quickly, the stirring is difficult, hot issues shift intensified reaction, prone to implosion phenomena. This research used easy heat dissipation and temperature control solution to prepare poly vinyl acetate resin polymerization, solvent is methanol (reaction temperature and the boiling point close to), initiator azo isobutyronitrile (two, reaction temperature on the decomposition temperature range).

The impinging stream reaction precipitation and low temperature solid state reaction method of the preparation of nano Strontium Carbonate

The main purpose is the production of Strontium Carbonate color display glass, glass absorbs the preparation of Strontium Carbonate by X - ray, and to improve the refractive index of glass, so a large number of nano Strontium Carbonate powder used for color TV picture tube glass screen glass, computer screens, such as manufacturing, reduce X - ray radiation on the human body. Here are two methods for the preparation of nano Strontium Carbonate as following:

1. Impinging stream reaction precipitation method:

In the submerged circulative impinging stream reactor, using strontium nitrate and ammonium hydrogen carbonate as raw material, by the reaction, legal HISTEP pure nano Strontium Carbonate product precipitation.

The experimental study on the effect of concentration, temperature, feed rate, reaction time and other factors on the yield of the product, nano Strontium Carbonate prepared products were characterized by XRD, crystallization effect is good, high purity, was characterized by TEM, the morphology is spherical or nearly spherical, the average particle size in 25nm.

The method is simple, narrow particle size distribution, can be recycled materials and is easy for industrialized production.

2. Low temperature solid state reaction method:

In the condition of the whole reaction thermodynamics feasible, molecules involved in the solid state reaction can carry out long distance movement and the reactant sufficiently contact and react, molecular production, when the crystal nucleus appeared product molecules accumulated to a certain amount, the nucleation and growth to a certain size is independent crystal phase.

Scientists has based on low temperature solid state chemical reaction technology, with six water strontium chloride and sodium carbonate as raw material is mixed and ground under the action of a catalyst, the solid state reaction synthesis of nano Strontium Carbonate powder, the grinding time, temperature, precipitation and the effect of surfactant on the reaction. XRD and TEM characterization of product, that product is pure Strontium Carbonate, its size is 50-80nlTl, and the intensity distribution.

The method has the advantages of simple process, high conversion rate of uniform particle size, programmable, easy realization of industrial production, mainly reflects the process without the use of solvents, consistent with the concept of green chemistry.

The advantages and disadvantages of Natural Pigment

Natural food colorant (pigment) is a kind of edible pigment obtained by the natural resources. Mainly from animal and plant tissues and microorganisms to extract pigment, and the colorants is in the majority of plant. Natural Pigment has not only to the role of food coloring, but also is a considerable part of Natural Pigment has the physiological activity.

The advantages of Natural Pigments:

1. Most Natural Pigments are from animal and plant tissue, therefore, generally on the high security to people.

2. Some Natural Pigment itself is a kind of nutrients, has nutrition effects, some also have a certain pharmacological effects.

3. It can be better able to mimic the natural color, the color tonal is more natural.

The limitations of Natural Pigment in application:

1. The solubility of it is small, it is not easy to color uniformity.

2. The pigment concentration is generally small, dyed the gender is poo, some natural edible pigment and food raw materials produce chemical reaction and discoloration.

3. The fastness of it is poor, and greatly affected by PH, oxidation, light, temperature and so on.

4. Because it has been extracted from natural plants, sometimes affected by its coexisting ingredients or have their own peculiar smell.

5. It is difficult for Natural Pigment to color. Different colorant compatibility is poor, it is difficult to deploy a arbitrary hue.

6. It is susceptible to metal ions and water quality impact. Edible Natural Pigment is easy to occur in metal ion catalyzed decomposition, discoloration or formation of insolubles salts.

7. The composition of it is complicated, improper use of it is easy to produce precipitation, opacity, and the pure product cost is high.

8. The products are quite different, Natural Pigments are basically is a mixture of several components, but the same colorant due to different sources, different processing methods, and the ingredients are also different.

9. The properties of Natural Pigment are less stable than the synthetic pigment, when we use it, we need to add protective agents, and this have some adverse effects on the use of pigment.

10. In most cases, the cost of Natural Pigment is much higher than the cost of synthetic pigment.

The preparation of PVA spinning dope

At present, in the mass production with water as solvent for preparing Polyvinyl Alcohol ( PVA ) spinning dope. The process of it is as following:

1. Washing and dewatering:

The objective of washing is to reduce the water content of Sodium Acetate in Polyvinyl Alcohol material, and is make it not more than 0.05 % to 0.2 %, otherwise, it will make the fiber alkaline coloring occur during heat treatment. Through washing, it also can remove the material part of low relative molecular mass Polyvinyl Alcohol, improve its relative molecular mass and polydispersity. In addition, the process of washing, PVA occurred moderate swelling, facilitates the dissolution. The process of washing is the main regulating the temperature of washing and washing water. Content of sodium acetate as in long net type washing machine mainly depends on the regulation to control the temperature of washing water after washing the Polyvinyl Alcohol, the groove binding type washing machine is to regulate the washing water quantity, water temperature should not exceed 30 to 40 ℃, water consumption is about 10t / T  (PVA). Polyvinyl Alcohol need to dewatering after washing and to ensure that the water content of sodium acetate Polyvinyl Alcohol after washing and stable rate. The former in order to avoid alkaline coloring fiber during heat setting, the latter in order to avoid the concentration of dissolved when the control is difficult. The control index of moisture or crush rate.

2. Dissolution:

After washing the Polyvinyl Alcohol through intermediate storage and weighing distribution is fed into a dissolving machine, dissolved with hot water. Concentration of PVA water solution wet spinning with 14% to 18%, dry spinning dope concentration is 30% to 40%. Sometimes in the Polyvinyl Alcohol dissolved while also adding appropriate additives, to meet the needs of different types of Polyvinyl Alcohol fiber production.

In the actual production of Polyvinyl Alcohol, dissolved generally under pressure in the 95 to 98 ℃. According to the different concentration of solution preparation, dissolution time can be varied from 2 to 8h. The concentration of the solution is dissolved, the longer the time required.

Liquid viscosity is the need for strict control of the dissolution process parameters. The average degree of polymerization of 1750 soil 50 Polyvinyl Alcohol, with concentration of 15% aqueous solution, the viscosity of 135s, the concentration of aqueous solution of 16% of the viscosity is of 180s.

3. Mixing, filtering and deaeration;

After dissolving Polyvinyl Alcohol spinningsolution was not immediately used for spinning, must be in constant temperature (96 to 98 ℃) by mixing, filtering and deaeration. Mixed in a large capacity equipment, filtration by filter press; deaeration still static batch deaeration, such as the use of high efficient continuous defoaming, it must be in the protection of saturated steam, to prevent excessive evaporation of surface level and crust.