Dry Blending

Process of the Dry Blend Department

Main Materials

This is the starting point of PVC Product Process. To get qualified product, you have to use standardized materials. Raw materials must test by Quality Assurance Department or Raw materials must have Technical Data Sheet including test reports before it pass to Dry Blending Process.

 The additives found in PVC help make it one of the most versatile, cost-efficient materials in the world. Without additives, literally hundreds of commonly used PVC products would not exist. Many materials are useless until they undergo a similar modification process. Steel, for instance, contains among other things, chromium, nickel and molybdenum. PVC’s are tailored to the requirements using sophisticated additives technology.

PVC Resins

This is the most important part of PVC Compound. Quality Assurance Department must test Bulk Density, Sieve Analysis, Flow Time K-Value test before it pass to process.

Fillers

Filler is useful to strong the product and using Filler purpose you can decrease the product cost. You can use Calcium Carbonate ( CaCO3 ) as a Filler. Quality Assurance Department must test Moisture Content and Unparticle Content before it pass to process.

Stabilizer

This is very useful to protect PVC Resin when it in Extruder Barrel. Because when PVC Resin in Extruder Barrel, it try to decompose. But when PVC Resin in Extruder Barrel with Stabilizer, PVC Resin only try to melt. Because Stabilizer get extra temperature of PVC Resin.
These are the most popular Stabilizers.

• Baerlocher Bearopan
• Advapak NEO

• Dibasic Lead Phosphite
• Dibasic Lead Stearate
• Tribasis Lead Stearate
• Normal Lead Stearate

Lead stabilizers, particularly tribasic lead sulfate is commonly used in plasticized wire & cable compounds because of its good non-conducting electrical properties.

Organotin stabilizers are commonly used for rigid PVC, including for pipe, fittings, windows, siding profiles, packaging and injection molded parts. These repair unstable sites on PVC removing unstable chlorine and replacing it with a ligand from the tin stabilizer molecule. This produces stability at least an order of magnitude better than without stabilizer. Examples of effective tin compounds are di-alkyl tin dilaurate,  mono-alkyl tin, di-alkyl tin, diisooctyl thioglycolate. Certain grades of methyl tins and octyl tins are used in food contact applications.

Antimony tris(isooctylthioglycolate) has found use in pipe formulations at low levels. Its disadvantage is it cross-stains with sulfide based tin stabilizers.

Barium-zinc stabilizers have found use in plasticized compounds, replacing barium-cadmium stabilizers. These are used in moldings, profiles, and wire coatings. Cadmium use has decreased because of environmental concerns surrounding certain heavy metals. Calcium-zinc stabilizers are used in both plasticized PVC and rigid PVC for food contact where it is desired to minimize taste and odor  characteristics. Applications include meat wrap, water bottles, and medical uses. Many stabilizers require co-stabilizers. Several organic co-stabilizers are quite useful with barium-zinc and calcium-zinc stabilizers. They are beta diketones, epoxies, organophosphites, hindered phenols, and polyols.

Lubricant

This is very useful to Polymerization Process. When it with PVC Compound, product will very strong and surface will very shine.

Internal Lubricant = Calcium Stearate
External Lubricant = Stearic Acid

Many authors classify lubricants as “internal” or “external”. Internal lubricants were considered to be soluble in PVC, or considered to have little effect on fusion, or they reduce melt viscosity; external lubricants were
considered to retard fusion or to promote metal release. This system of classifying lubricants has too many conflicting measurements to be consistent and useful. Others have shown classifications based on synergy between various lubricants, but did not explain the nature of that synergy. A model for the lubrication mechanism has been developed which explains synergy between certain lubricants. This model treats lubricants as surface active agents. Some lubricants have polar ends which are attracted to other
polar ends and to polar PVC flow units and to polar metal surfaces. These also have non-polar ends which are repelled by the polar groups. Synergy happens when non-polar lubricants are added, which are attracted to the non-polar ends and act as a slip layer.

Pigment

TiO2 can use as Pigment.Titanium is the ninth most common element in the earth’s crust and is present naturally as the minerals rutile (TiO2), ilmenite (FeTiO5)and sphene (CaSiTiO5) among others.
These are the most popular Pigments

• DuPont
• Tioxide

Impact modifiers

In the early days of plastics, many unplasticized PVC products were brittle. This gave plastics a cheap reputation. It was therefore quite desirable to develop technology to produce tough plastics. In the early 1950s, The Geon Company (then a part of BFGoodrich) began adding rubbery polymers to PVC to
improve toughness. Rubbery particles act as stress concentrators or multiple weak points, leading to crazing or shear-banding under impact load. This can result in cavitation and/or cold drawing, thus allowing the PVC to absorb large amounts of energy.

 Processing aids

PVC often flows as billion molecule primary particles. Processing aids glue these particles together before the PVC melts, thus acting as a fusion promoter. Processing aids also modify melt rheology by increasing melt elasticity and die swell, or, some reduce melt viscosity, and they reduce melt fracture. Some processing aids lubricate to reduce PVC sticking to metal. And processing aids affect dispersion of fillers, impact modifiers, and pigments. The most common processing aids are high molecular weight acrylics based primarily on polymethylmethacrylate copolymers.

 Plasticizers

In 1926 at The Geon Company (then BFGoodrich), solutions of PVC, prepared at elevated temperatures with high boiling solvents, possessed unusual elastic properties when cooled to room temperature. Such solutions are flexible, elastic, and exhibit a high degree of chemical inertness and solvent resistance.

This unusual behavior is due to unsolvated crystalline regions in the PVC that act as physical crosslinks, but allow the PVC to accept large amounts of solvent (plasticizers) in the amorphous regions, lowering its Tg to well below room temperature, thus making it rubbery. Thus PVC was the first thermoplastic elastomer (TPE). This rubber-like material has stable properties over a wide temperature range.

A few plasticizers impart specific properties for particular applications. For example, citrate esters are used in food contact applications, benzoates are used for stain resistance, and chlorinated hydrocarbons impart flame resistance and good electrical properties. Aliphatic diesters offer good low temperature flexibility; linear alcohol based phthalates offer good low temperature flexibility and also have reduced volatility; phosphates improve flame resistance; trimellitates have low volatility, are used for high temperature applications, and also have good low temperature properties. Polymeric plasticizers do not migrate easily but suffer from poor low temperature flexibility. Epoxy plasticizers are also good plasticizers with low volatility and they act as costabilizers, improving the thermal stability of PVC.


Common PVC plasticizers.


Aliphatic ester

di(2-ethylhexyl) adipate   ( DOA )
di(2-ethylhexyl) azelate
di(2-ethylhexyl) sebacate

Phthalate

di(2-ethylhexyl)    ( DOP or DEHP )
diisooctyl    ( DIOP )
diisodecyl   ( DIDP )
butylbenzyl   ( BBP )
butyloctyl    ( BOP )
diisononyl    ( DINP )
ditridecyl    ( DTDP )
diundecyl   ( DUP )
linear C7-C11    ( 711 phthalate )
di(2-ethylhexyl) terephthalate     ( DOTP )

Phosphates

trioctyl    ( TOP )
cresyl diphenyl    ( CDP )
tricresyl    ( TCP )
triphenyl
tri(2-ethylhexyl)    ( TEHP )

Trimellitates

tris(2-ethylhexyl)     ( TOTM )
triisooctyl      ( TIOTM )

Epoxies

epoxidized soybean oil     ( ESO )
epoxidized linseed oil
epoxy stearate
2-ethylhexyl epoxytallate

Plasticizers and stabilizers in particular have been researched at length to determine their potential impact on human health and the environment. DEHP (di-2-ethylhexyl-phthalate) has been used worldwide in  applications such as blood bags, saline solutions, meat wraps and other highly credible uses, however, there has been much debate over that impact due to the differing methods used to evaluate them. (Please note that additional information is rapidly becoming available and the reader may want to update this information in
the years following publication of this article). While the U.S. National Toxicology Program and the International Agency for Research on Cancer have classified the plasticizer DEHP as a possible human carcinogen, their methodologies have been criticized for potentially inaccurately ascribing results obtained with rodents to humans. Mechanistic studies indicate that the carcinogenic response which DEHP produces in rodents is directly related to physiologic and metabolic changes that are specific to that species. Because the evidence indicates the response is an artifact to that species and not a true indication of human hazard, a number of regulatory bodies do not consider DEHP to pose a hazard to man. The Specialized Experts Working Group of the European Commission for instance, has concluded that there is no evidence to warrant the classification of DEHP as a carcinogen. DEHP is not regulated as a carcinogen by the U.S. Food & Drug Administration, which has long governed the plasticizer's use in medical devices and in food contact applications. DEHP-plasticized PVC is used in medical applications like blood bags where it is known to actually protect red blood cells from deterioration. Flexible PVC film is considered the most desirable material for wrapping meats, as it is oxygen-permeable and maintains the bright red color needed to make meats salable to consumers, as well as extending the shelf life of meats.

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