include plasticizers, heat stabilizers, fillers, lubricants, processing aids, and other additives. It should be noted that PVC resin, of themselves, are of no practical use.
It should be noted that PVC resin, of themselves, are of no practical use. When fused, they are hard, brittle compounds. Their inherent limited heat stability makes any type of processing difficult if not impossible. Therefore, in order to produce a useful product other ingredient is added to the PVC resin for the purpose of: increasing flexibility, providing adequate heat stability, improving process ability, imparting aesthetic appeal.
Let’s consider these ingredients in some detail.
Plasticizers are low boiling liquids or low molecular weight solids that are added to resins to alter processing and physical properties. They increase resin flexibility, softness and elongation. They increase low temperature flexibility but decrease hardness. They also reduce processing, temperatures and melt viscosity in the case of calenering.
Plasticizers fall into two categories based on their solvating power and compatibility with resins.
a. Primary Plasticizers: are able to solvate resins and retain compatibility on aging. Samples of these would be:
DOP: Dioctyl phthalate
S-711: Di (n-hexyl; n-octyl; n-decyl) phthlate (linear)
DIDP: Di-iso decyl phthate
b. Secondary Plasticizers: are so defined because of their limited solubility and compatibility and are, therefore, used only in conjunction with primary plasticizers. The ratio of primary to secondary depends on the type and quantity of the particular plasticizers. Secondary plasticizers are used to impart special properties such as:
-low temperature flexibility
DMODA (di-normal octyl decyl adipate)
DOZ (di-octyl azelate)
DOA (di-octyl adipate)
Flame retardance Reofas 65 (tri-iso propyl phenyl phosphate)
Electrical properties t tri-mellitates
Cereclor, chlorinated parafins
In a separate category are the polymeric plasticizers. These are long chain molecules and are made from adipic, azelaic, sebacic, acids and propylene and butylene glycols. The efficiency of polymerics is poor but volatility and migration are superior. An example of a polymeric plasticizer is Paraplex G-54.
The characteristics sought in plasticizers can be summarized as follows:
1). efficiency- This is the level or concentration needed to give a stated hardness, flexibility or modulus.
2). the effect on low temperature flexibility.
3). solvating power: This influence the fluxing rate of the compound at a given temperature or at a minimum fluxing temperature.
The fluxing rate relates directly to processing time.
Performance: This relates to volatility, extraction resistance, compatibility.
The chief purpose of a heat stabilizer is to prevent discoloration during processing of the resin compound. Degradation begins with the evolution of Hydrogen Chloride, at about 200 ℉ increasing sharply with time and temperature. Color changes parallel the amount of degradation running from white to yellow to brown to black. Therefore, the need for heat stabilizers.
The most effective stabilziers have been found to be:
1). Metal soaps: Barium-cadmium solids and liquids: Mark 725, Mark 311
2). Organo tin compounds: octyl tin mercaptide: Mark OTM
3). Epoxies: epoxidized soya oil (G-62)
The above are most likely most effectively only when used in combination (synergism).
What are some of the criteria in choosing a stabilzier system?
1). The ability to prevent discoloration
2). The amount of lubrication involved. In calandering this can be of critical importance. Mark 725 has low lubricating effect while Mark 311 contributes high lubrication effect.
3). Plate-Out- a potential side-affect of processing and has been linked to certain barium-cadium stabilizers.
4). Compatability with the resin system- for obvious reasons.
5). Resistance to sunlight staining: atmospheric discoloration.
Essentially fillers are added to formulations to reduce costs, although they may offer other advantages – such as opacity, resistance to blocking, reduced plate-out, improved dry blending. On the other side, fillers can reduce tensile and tear strength, reduce elongation, cause stress whitening, reduce low temperature perforance.
The most common fillers used with PVC are calcined clays, and water-ground and precipitated calcium carbonates of particle size around 3 micrometers. Other fillers are silicas and talcs.
These materials are of prime importance in PVC processing. They are decribed below.
1). Improve the internal flow characteristics of the compound.
2). Reduce the tendency for the compound to stick to the process machinery
3). Improve the surface smoothness of the finished product
4). Improve heat stability by lowering internal and/or external friction
Examples of lubricants, with which you may be familiar, are stearic acid, calcium stearate, Wax E, polythylene AC 617.
These may be regarded as low-melt viscosity, compatible solid plasticizers. They are added to lower processing temperature, improve roll release on calendars, reduce plate-out, promote fusion.
They are usually added at concentration of 5.0%. The most widely used processing aids are acylic resins of which acrylic K 120N is an example.
There are several other additives which we will list and comment on briefly.
1). Impact Modifiers: These are used in rigid vinyls to improve impact resistance. These are usually acrylic or ABS polymers used at 10-15 phr levels. Examples are Kureha BTA 111, Blendex 301.
2). Light Stabilizers: for resistance to ultraviolet radiation. They are used in low concentrations 0.5-1.5 phr.
3). Flame Retardants: PVC is inherently self-extinguishing However, the plasticizers and additives are not. Therefore, flame retardants are added. The most widely known one is antimon tri-oxide.
4). Anti-Static Agents
5). Fungicides: Vinyzene BP-5
6). Foaming Agents: Chemicals that decompose at predetermined temperature to produce a certain volume of gas within the molten vinyl and thereby create foam.
7). Colorants: Both pigments and dyes can be used. However, dyes, which are soluble organic substances, are used sparingly de to their tendency toward migration and extract ability. Heat resistance of colorants must be carefully evaluated.
In summary, we have seen that a vinyl compound consists of following components: PVC resin, plasticizer, heat stabilizer, lubricant, special additive, colorants.