⁠POLYMER ADDITIVES

Metallic Stearates (Metallic Soaps)

Metallic stearates are metal salts of stearic acid (C₁₇H₃₅COOH), commonly used as multifunctional additives in the plastics, rubber, cosmetics, and pharmaceutical industries. In PVC applications, they serve as lubricants, co-stabilizers, and processing aids, particularly in combination with heat stabilizer systems.

Chemical Composition:

Metallic stearates are typically formed by reacting stearic acid with metal oxides or hydroxides. Common types include:

• Calcium Stearate (Ca(C₁₇H₃₅COO)₂)
• Zinc Stearate (Zn(C₁₇H₃₅COO)₂)
• Magnesium Stearate (Mg(C₁₇H₃₅COO)₂)
• Aluminum Stearate (Al(C₁₇H₃₅COO)₃)
• Barium Stearate (Ba(C₁₇H₃₅COO)₂)

• Lubrication: Reduce friction between polymer melt and processing equipment
• Co-stabilization: Assist primary heat stabilizers in scavenging HCl during PVC degradation
• Release Agent: Prevent sticking to molds or rollers during processing
• Dispersion Aid: Improve the dispersion of fillers, pigments, and other additives

Applications:

• Rigid and flexible PVC
• Masterbatches and one-pack stabilizer systems
• Polyolefins, rubbers, and engineering plastics
• Powder coatings and greases (non-PVC sectors)

Advantages:

• Thermally stable at PVC processing temperatures
• Compatible with most stabilizer systems (lead-based, Ca-Zn, Ba-Zn, organotin)
• Available in various physical forms (powder, granule, micronized)

PVC Processing Aids

PVC Processing Aids are high molecular weight acrylic polymers or functional additives used to improve the melt processing behavior of PVC during extrusion, calendaring, or molding. They do not act as plasticizers, but rather as polymeric additives that enhance fusion, melt strength, surface quality, and overall process efficiency—without compromising the final mechanical properties of the product.

These aids are especially critical in rigid PVC formulations, where proper gelation and melt homogeneity are essential for achieving optimal performance.

Functions of Processing Aids in PVC:

• Promote PVC Fusion: Lower fusion time and energy consumption by improving melt homogeneity
• Improve Melt Strength: Enhance shape retention and dimensional stability during extrusion
• Enhance Surface Finish: Minimize surface roughness, sharkskin, and die lines
• Aid Filler Dispersion: Improve distribution of pigments, calcium carbonate, and other fillers
• Increase Output: Allow faster processing and reduced torque load on machinery

Processing aids are typically categorized based on their functionality and polymer compatibility:

Purpose: Improve fusion, melt strength, and surface appearance.
Composition: Methacrylate or acrylate copolymers with high molecular weight.
Applications: Rigid PVC pipes, profiles, sheets, and foamed products.
Common Grades: PA-20, PA-30, ACR-401, ACR-530, etc.

2. Lubricating Processing Aids

Purpose: Enhance melt flow and internal/external lubrication for better release and reduced shear.
Composition: Low molecular weight acrylics or polyethylene wax blends.
Applications: Thin films, foamed sheets, extrusion lines with complex dies.

3. Foam Regulators (Foaming Aids)

Purpose: Control cell structure and expansion ratio in foamed PVC products.
Composition: Ultra-high molecular weight acrylics designed to stabilize foam structure.
Applications: Celuka foam boards, WPC panels, PVC foam sheets and profiles.

Impact Modifiers for PVC

Impact modifiers are polymeric additives used to enhance the impact resistance and toughness of PVC products, particularly in applications where durability and resistance to fracture or breakage are critical. These modifiers work by dispersing energy during an impact, preventing brittle fracture and improving the material’s ability to withstand external forces, especially at low temperatures.

Impact modifiers do not significantly affect the PVC’s basic mechanical properties, such as rigidity or chemical resistance, but they provide essential improvements in impact strength, elongation at break, and stress crack resistance.

Types of Impact Modifiers

The selection of impact modifiers depends on the desired balance of impact strength, processing conditions, and final product performance. The most common types of impact modifiers for PVC include:

Composition: Chlorinated polyethylene, a thermoplastic polymer modified with chlorine atoms.
Mechanism: The chlorine modification enhances the polymer’s compatibility with PVC, improving its impact resistance while maintaining rigidity.
Applications: Window profiles, siding, fences, and other exterior products requiring high-impact strength and weather resistance.
Features:

• Good low-temperature impact resistance
• Suitable for rigid PVC formulations

2. Methyl Methacrylate-Butadiene-Styrene (MBS)

Composition: A graft copolymer of methyl methacrylate (MMA), butadiene (rubber), and styrene.
Mechanism: The rubber phase (butadiene) provides excellent energy absorption, while the MMA component contributes to improved impact strength and clarity.
Applications: Transparent rigid PVC products, such as signage, profiles, and decorative sheets.
Features:

• Exceptional clarity and gloss retention
• Excellent processing stability
• Good toughness and impact resistance, particularly at low temperatures

3. Acrylic Impact Modifiers

Composition: Modified acrylic polymers, often in a core-shell structure.
Mechanism: The core material (rubber) provides energy dissipation, while the shell (acrylic) improves mechanical properties and compatibility with PVC.
Applications: Rigid PVC applications like Door & Window profiles, PVC sheet, and cooling tower fills.
Features:

• Good impact resistance without compromising gloss
• Ideal for low-temperature applications

Composition: Styrene-butadiene copolymer.
Mechanism: The rubber phase provides toughness and the styrene phase contributes to rigidity.
Applications: Used in flexible PVC formulations and PVC composites where toughness and flexibility are needed.
Features:

• Good low-temperature impact resistance
• Enhances flexibility and bendability
• Used in products like pipes, hoses, and automotive parts

• Building & Construction: Profiles, window frames, siding, roofing, and decorative elements
• Automotive: Interior trim, bumpers, and under-the-hood components
• Packaging: Rigid containers, bottles, and food packaging
• Electrical: Cable sheathing and wire insulation

Antioxidants

Antioxidants are chemical additives used in polymer formulations to prevent oxidative degradation during processing, storage, and end-use. In PVC and other thermoplastics, exposure to heat, oxygen, shear, and UV light can generate free radicals, which lead to chain scission, discoloration, loss of mechanical properties, and ultimately material failure. Antioxidants act by stabilizing or neutralizing these radicals, thereby enhancing the thermal-oxidative stability and service life of the polymer.

• Prevent thermal degradation during melt processing (extrusion, molding)
• Protect against oxidative aging during storage and use
• Preserve color, flexibility, and strength of the final product
• Improve process stability, especially under high shear and temperature

Antioxidants are broadly categorized based on their mechanism of action and chemical structure:

Function: Neutralize free radicals formed during thermal or oxidative stress.

Mechanism: Donate hydrogen atoms to stop the propagation of free radical chain reactions.

Common Types:

• Hindered Phenols (e.g., BHT – Butylated HydroxyToluene, Irganox® 1010, Irganox® 1076)
• Aminic Antioxidants (e.g., Diphenylamine derivatives – mainly used in rubbers)

Applications: Protect polymers during both processing and service life; widely used in PVC, PE, PP, and elastomers.

2. Secondary Antioxidants (Hydroperoxide Decomposers)

Function: Decompose hydroperoxides into non-radical, stable products, preventing further radical formation.

Mechanism: React with hydroperoxides before they break down into free radicals.

Common Types:

• Phosphites (e.g., Tris(nonylphenyl) phosphite – TNPP, Irgafos® 168)
• Thioethers

Applications: Highly effective during processing; typically used in combination with primary antioxidants for synergistic effect.

Function: Enhance the performance of primary and secondary antioxidants.

Examples:

• Lactones and polymeric stabilizers
• UV absorbers (when combined for UV resistance)

Applications: Used in specialized PVC formulations where long-term aging resistance or UV protection is needed.

• Processing temperature and residence time
• Compatibility with other additives (stabilizers, lubricants, pigments)
• Color stability requirements (clear vs. opaque PVC)
• Regulatory compliance (food contact, medical use, RoHS, REACH)

• Rigid and flexible PVC compounds
• Cables and wires (to protect dielectric properties)
• Pipes, profiles, and sheets
• Masterbatches and one-pack stabilizer systems
• Foamed and colored PVC products

Flame Retardants

Flame retardants are chemical additives incorporated into plastics like PVC to reduce flammability, delay ignition, suppress smoke, and inhibit fire propagation. These additives function by interfering with the combustion process through gas-phase radical quenching, heat absorption, char formation, or inert gas release.

Flame retardants are generally categorized by chemical nature and mechanism of action. Below is a detailed classification of all major types:

Chemical Basis: Brominated or chlorinated organic compounds

Mechanism: Release halogen radicals (Cl•, Br•) that scavenge flame-propagating radicals (H•, OH•) in the gas phase, effectively suppressing the flame.

Examples:

• Decabromodiphenyl ether (Deca-BDE)
• Tetrabromobisphenol A (TBBPA)

2. Antimony Trioxide (ATO) – Synergist Flame Retardant

Chemical Formula: Sb₂O₃

Type: Synergist, typically used in combination with halogenated flame retardants

Mechanism: Enhances the effectiveness of halogenated compounds by forming volatile antimony halides in the gas phase, which interrupt flame propagation more efficiently.

Typical Loading: 1–10% depending on formulation

Applications:

• PVC cables and jackets
• Electronics
• Flame-retardant coatings

Pros:

• Highly effective in halogenated systems
• Improves smoke suppression

Cons:

• Not effective alone
• Classified as a suspected carcinogen (handling precautions required)

3. Inorganic Flame Retardants

a. Aluminum Trihydrate (ATH) 

Formula: Al(OH)₃
Mechanism: Decomposes endothermically around 200°C, releasing water vapor and cooling the substrate.
Applications: Wire & cable, roofing membranes
Advantages:

• Smoke suppression
• Halogen-free, non-toxic

b. Magnesium Hydroxide (MDH)

Formula: Mg(OH)₂
Mechanism: Decomposes at ~330°C, suitable for high-temp polymers
Applications: Automotive components, flame-retardant TPO
Advantages:

• Halogen-free
• Better thermal stability than ATH

4. Phosphorus-Based Flame Retardants

Mechanism:

• Promote char formation in the condensed phase, creating a barrier that insulates the polymer.
• In gas phase, phosphorus radicals inhibit combustion reactions.

Types:

• Organic phosphates (e.g., triaryl phosphates, resorcinol diphosphates)
• Inorganic phosphates (e.g., Ammonium Polyphosphate, APP)

Applications: Foamed PVC, textiles, automotive interiors, electronics

Advantages:

• Effective in both gas and condensed phases
• Can be halogen-free

5. Synergistic Flame Retardant Systems

These are combinations of two or more flame retardants to enhance overall efficiency:

• ATO + Halogen compound → high efficiency, low dosage
• APP + Melamine + Pentaerythritol → intumescent systems
• Phosphite + phenolic antioxidant → dual thermal/oxidative and flame protection

Waxes

Waxes are a class of low-molecular-weight organic compounds that are solid at room temperature but melt at relatively low temperatures (typically between 50°C and 150°C). In PVC and plastic processing, waxes are used primarily as lubricants, processing aids, release agents, and surface modifiers.

Their molecular structure typically consists of long-chain hydrocarbons or esters, and they may be of natural, synthetic, or petrochemical origin.

• Internal Lubrication: Reduce friction between polymer chains during melt processing, improving flow.
• External Lubrication: Reduce friction between the polymer and metal surfaces (e.g., extruder barrel, die), preventing sticking.
• Fusion Control: Regulate PVC gelation and melt viscosity.
• Release Agent: Prevent sticking of finished parts to molds or rollers.
• Gloss and Surface Finish: Enhance surface smoothness and appearance of final products.

Types of Waxes

Waxes are generally classified by their origin and chemical composition. Below are the major types used in plastics and PVC applications:

1. Polyethylene (PE) Waxes

Type: Synthetic or by-product of polyethylene production
Structure: Linear or branched saturated hydrocarbons (C18–C50)

Variants:

• Low-Density PE Wax
• High-Density PE Wax
• Oxidized PE Wax (contains polar functional groups for improved dispersion)

Properties:

• High hardness
• Low melt viscosity
• Excellent external lubricity

Applications:

• PVC pipes and profiles
• Masterbatches
• Hot melt adhesives
• Powder coatings

2. Polypropylene (PP) Waxes

Structure: Similar to PE wax but with propylene monomer units

Properties:

• Higher melting point than PE wax
• High crystallinity and thermal stability

Applications:

• Injection molding
• Toners
• PP masterbatches

3. Fischer-Tropsch (FT) Waxes

Type: Synthetic waxes made via the Fischer-Tropsch process (coal or natural gas to wax)

Structure: Highly linear saturated hydrocarbons

Properties:

• Very high melting point (90–110°C)
• Excellent hardness and low volatility

Applications:

• PVC extrusion (internal/external lubrication)
• Powder coatings
• Hot melt adhesives

4. Paraffin Waxes

Type: Petroleum-derived, refined from crude oil distillates
Structure: Straight-chain alkanes (C20–C40)

Properties:

• Low melt viscosity
• Economical
• Moderate lubricating properties

Applications:

• Flexible PVC compounds
• Candles, packaging
• Mold release agents

5. Amide Waxes (e.g., Erucamide, Oleamide, Stearamide)

Type: Fatty acid amides

Properties:

• Excellent slip and anti-blocking
• Blooming behavior (migrate to the surface)

Applications:

• Films and flexible PVC
• Injection molded parts

Plasticizers

Plasticizers are low-volatility organic compounds added to polymers—especially PVC (Polyvinyl Chloride)—to increase flexibility, softness, and workability. They function by reducing the glass transition temperature (Tg) of the polymer, allowing chains to move more freely and lowering melt viscosity.

Plasticizers play a critical role in converting rigid PVC into flexible formulations suitable for applications like cables, films, hoses, synthetic leather, flooring, and medical products.

Mechanism of Action:

Plasticizers embed themselves between polymer chains, weakening intermolecular forces and increasing free volume, which:

• Enhances flexibility
• Reduces brittleness
• Improves low-temperature performance
• Aids in processing

Plasticizers are categorized based on chemical structure, compatibility, and performance. The main types are:

1. Phthalate Plasticizers (Traditional / General-Purpose)

Structure: Di-esters of phthalic acid

Examples:

• Dioctyl Phthalate (DOP / DEHP)
• Diisononyl Phthalate (DINP)
• Diisodecyl Phthalate (DIDP)

Applications: Wires, cables, flexible PVC, flooring, toys

Advantages:

• Excellent plasticizing efficiency
• Low cost
• Proven performance

Limitations:

• Regulatory restrictions due to toxicity concerns (e.g., banned in children’s toys in EU/US)

2. Terephthalate Plasticizers (Low Toxicity Alternative to Phthalates)

Structure: Esters of terephthalic acid (isomer of phthalic acid)

Examples:

• Di(2-ethylhexyl) terephthalate (DOTP)
• Diisononyl terephthalate (DINCH)

Applications: Toys, medical devices, food packaging

Advantages:

• Good plasticizing efficiency
• Lower migration and volatility
• Better regulatory compliance (phthalate-free)

3. Adipate Plasticizers

Structure: Esters of adipic acid

Examples:

• Di-2-ethylhexyl adipate (DOA)
• Diisononyl adipate (DINA)

Applications: Cold-flexible applications (e.g., outdoor cables, films)

Advantages:

• Excellent low-temperature flexibility
• Low volatility
• Compatible with PVC

4. Sebacate Plasticizers

Structure: Esters of sebacic acid (dicarboxylic acid)

Examples:

• Dioctyl sebacate (DOS)
• Diisodecyl sebacate (DIDS)

Applications: High-performance aerospace, automotive cables, cold weather applications

Advantages:

• Very low-temperature resistance
• Good aging and migration resistance

Limitations:

• Higher cost

5. Epoxy-Based Plasticizers (Also Function as Stabilizers)

Structure: Epoxidized fatty acid esters

Examples:

• Epoxidized Soybean Oil (ESBO)
• Epoxidized linseed oil

Applications: Rigid and flexible PVC, packaging, automotive

Advantages:

• Dual function: plasticizer and thermal stabilizer
• Low volatility
• Enhances heat and UV resistance

6. Trimellitate Plasticizers

Structure: Esters of trimellitic acid

Examples:

• Trioctyl trimellitate (TOTM)
• Triisononyl trimellitate (TINTM)

Applications: High-temperature cables, medical tubing, military use

Advantages:

• High thermal stability
• Excellent permanence (low migration)

Limitations:

• Expensive compared to general-purpose plasticizers