Common Types of Plastic Stabilizers

[US Masterbatch] In the plastics industry, maintaining the durability and mechanical properties of products under environmental exposure is a significant challenge. Plastic stabilizers play a critical role in protecting the polymer structure from degradation processes.

Common Types of Plastic Stabilizers

1. Heat Stabilizers

PVC resin is a primary example of a thermally unstable material. At temperatures exceeding 140°C, PVC begins to decompose and release hydrogen chloride (HCl) gas before reaching a plasticized state. Heat stabilizers are incorporated to:

• Inhibit the dehydrochlorination reaction (removal of HCl) during processing.
• Maintain the original color and mechanical properties when the material is exposed to high temperatures in extruders or injection molding machines.
• Common applications include the production of PVC compounds for electrical cables, water pipes, and various plastic films.

2. UV Stabilizer

Ultraviolet (UV) radiation from sunlight possesses sufficient energy to break chemical bonds in polymers, leading to “plastic aging”, characterized by surface chalking, cracking, or discoloration. There are two primary categories of UV stabilizer:

• UV Absorbers: These function by absorbing harmful UV radiation and converting it into harmless thermal energy before it can attack the polymer chains.
• HALS (Hindered Amine Light Stabilizers): These act as free radical scavengers. Rather than absorbing light, they trap free radicals formed during photo-oxidation, thereby preventing them from reacting with polymer molecules.

3. Antioxidants

Oxidation can occur during processing (thermo-oxidation) or throughout the product’s service life.

• Primary Antioxidants: Typically phenolic compounds, providing long-term protection for the product.
• Secondary Antioxidants: Typically phosphite compounds, protecting the plastic from degradation specifically during high-temperature thermal processing.

Practical Applications of Plastic Stabilizers in Manufacturing

In general, the most common types of UV Stabilizers behave as UV absorbers and HALS and in some cases, more than one additive can be used to provide a higher level of UV stabilization.

– UV absorbers: This form of UV stabilizer, as the name suggests, absorbs the UV radiation to prevent the initiation of photo-oxidation reactions. Once absorbed the heat from the UV rays is dissipated through the polymer chain. Carbon Black, Benzotriazoles and hydroxy-phenyltriazines are examples of UV absorbers.

– HALS: Hindered Amine Light Stabilizers, or HALS, are a form of UV stabilizer that function by targeting and trapping the free radicals produced during photo-oxidation, preventing them from reacting with the polymer structure. HALS vary in their structure but generally have the 2,2,6,6-tetramethylpiperidine ring structure.

We will explore technical problems occurring to PP and PE items during UV exposure and discuss how UV stabilizers can be incorporated to effectively protect these products from sunlight damage.

1. PE Blown Film Application (Agricultural Mulch & Plastic Bags)

In PE film blowing technology (LDPE/LLDPE), plastic films are typically produced with a thickness ranging from 15 to 50 microns. Due to the high surface area exposure to sunlight, PE films are highly susceptible to aging.

• Problem: Without UV stabilizers, agricultural mulch films will degrade and lose structural integrity after only 1–2 months of exposure to intense sunlight and agricultural chemicals.
• Solution: Incorporating UV additives (specifically from the HALS group) enables PE films to withstand continuous UV radiation for 6–24 months.
• Benefit: Ensures the mulch film protects crops throughout the entire growing season, optimizing investment costs for end-users.

2. PP Injection Molding Application (Furniture, Pallets, Outdoor Trash Cans)

Polypropylene (PP) inherently possesses high mechanical strength but is extremely sensitive to UV radiation due to its specific chemical structure.

• Problem: PP injection-molded products used outdoors, such as stadium seating or plastic pallets, often exhibit “chalking” — a white powdery layer on the surface. This indicates surface degradation, which renders the product brittle and prone to fracture upon impact.
• Solution: A combination of UV absorbers and free radical inhibitors (HALS) is integrated into the material blending process prior to injection molding.
• Benefit: Maintains impact strength and surface gloss, allowing the product to withstand heavy impacts even after prolonged outdoor exposure.