A compound is defined as a substance formed when two or more elements are chemically bonded together. But how does PVC resin transform to vinyl compound?
New compound formulations are developed to meet an application requirement or a processing limitation. Chemists and formulation engineers create custom compounds by blending a variety of additives, modifiers and stabilizers with PVC resin to achieve specific properties.
The difference between rigid and flexible PVC compounds, in a word is – plasticizer.
Rigid PVC compounds sometimes listed as rPVC or uPVC (unplasticized) – have high hardness, excellent mechanical properties, and high melt point. These work well in some applications, such as deck and rail or for pipe fittings, but there are other applications that call for a less rigid, more malleable material.
Flexible PVC compounds are formulated to meet performance requirements for applications such as medical tubing, electrical wiring, automotive body side molding, and garden hose just to mention a few. They are also formulated with our customer’s processability needs in mind. Flexible PVC compounds contain plasticizers, softening agents which help give them “rubber like” properties.
Market needs, scientific advancements, regulatory guidelines and raw material economics compel R&D technicians and formulation engineers to push the envelope, looking for more versatile and cost-effective materials to use in their custom compound formulations. Due to their inherent versatility, vinyl compounds have proven to be very cost-effective materials across many markets and applications.
Below is a generalized list of the ingredients used in the formulation of vinyl compounds.
GENERALIZED LIST OF VINYL COMPOUND INGREDIENTS
| INGREDIENT CATEGORY |
DEFINITION |
COMMONLY USED |
DESCRIPTION |
|
PLASTICIZERS |
A substance added to a resin that promotes flexibility and inhibits brittleness |
Monomeric, Polymeric, Epoxy |
PVC compound is rigid at room temperature, which can make it difficult to process. Plasticizers, which are typically liquid chemical compounds, are added to PVC resin to make it flexible. The more plasticizer added to a compound, the softer and more flexible the PVC becomes. All flexible vinyl compounds contain plasticizers or alloys (see below) in order to make them less rigid and easier to process. |
|
STABILIZERS |
A chemical added to a solution, mixture or suspension to maintain it in a stable or unchanging stage |
Barium/Zinc liquids, Calcium/Zinc powders, Tin Mercaptides, Organic-based (Benzotriazoles and Benzophenones for UV stabilization) |
Stabilizers are essential in PVC compounds because PVC resin can degrade when exposed to elevated temperatures. Heat stabilizers help to diminish breakdown and enhance heat stability. UV stabilizers are used in compounds that may encounter direct, extended contact with sunlight. |
|
LUBRICANTS |
A substance used for minimizing friction |
Fatty Acids, Metallic Soaps, Esters, Waxes |
Lubricants are added to compounds to assist in the manufacturing process. They help with melt viscosity, compound flow, and to minimize both processing and molecular friction. |
|
FILLERS |
A substance added to a product to increase volume, opacity, or strength |
Calcium Carbonate, Kaolin Clay, Talc |
Fillers are solid materials of varying particle sizes used in the formulation of PVC compounds to improve impact performance, opacity and to add stiffness and tensile strength. Particle size and ratio of filler to resin are considerations when determining how much filler can be used without degrading the performance of a compound. |
|
FUNCTIONAL ADDITIVES |
A substance added to a compound in small quantities, typically to improve an aspect of performance |
Texturing agents, Impact Modifiers, Fungicides, Flame Retardant, Smoke Suppressant |
Several other types of additives may be introduced to a compound to enhance or create a unique property within the compound. (See: FireGuard®, HalGuard®, AquaGuard®). |
|
ALLOYING POLYMERS |
A polymer blend or mixture in which polymer(s) blend toegether with PVC to create a new material with different physical properties than PVC alone |
Thermoplastic Polyurethane, EVA, Nitrile Rubber |
Blends are created when PVC compound is blended with another polymer to achieve enhanced performance. Many times these blended compounds are used in harsh environments or when abrasion and chemical resistance is required. (See: Apex PVC Blends and Flexalloy®). |
For more than 60 years, as a material science and custom compounding innovator, Teknor Apex has focused on meeting the material challenges presented by new applications, the expanding marketplace, and modernization of processing technologies.
For more information on this topic, also see our blog - ‘How is PVC Made, Anyway?’
Contact the vinyl division for more information or to discuss any of your vinyl compound needs.
