Internal Factors Affecting the Anti-Ultraviolet Aging Performance of Plastic Products

The following is a systematic analysis and summary of the influence of main materials, filler masterbatch, color masterbatch and recycled materials on the anti-ultraviolet aging performance of plastic products based on the principles of material science and practical experience in the industry.

I. Influence of main material (matrix resin)

Difference between molecular structure characteristics and crystallinity

Polypropylene (PP) contains a lot of tertiary carbon in its molecular chain, which is easy to undergo free radical reaction under the action of ultraviolet rays, leading to photooxidative degradation, so its anti-ultraviolet aging performance is poor. Its crystallinity is at a medium level.

High density polyethylene (HDPE) has stable molecular chain structure and excellent ultraviolet resistance. The higher crystallinity makes the molecular chains closely arranged, which reduces the ultraviolet permeability and delays the aging process. However, the grain boundary region may become the starting point of ultraviolet aging because of stress concentration and many defects.

Low density polyethylene (LDPE) also has a stable molecular chain structure and good ultraviolet resistance. However, due to the low crystallinity, large intermolecular gap and relatively strong ultraviolet penetration, the overall anti-aging ability is slightly lower than that of HDPE.

II. Impact of Filling Masterbatches

1. Types and functions of fillers

Inorganic fillers (such as talcum powder and calcium carbonate): mainly reduce the UV penetration rate through physical shielding, but the mechanical properties of the material, especially the impact toughness, will be significantly deteriorated when the dosage exceeds 30%.

Functional filler: nano-TiO₂: it has UV reflection function, and needs surface modification (such as silane coupling agent) to improve dispersion and avoid agglomeration of nano-particles; Wollastonite: the unique fibrous structure can form a three-dimensional barrier network, effectively delaying the diffusion path of UV radiation.

2. Decentralization problem

If the filler masterbatch is poorly dispersed (common in high-filling systems), it will form stress concentration points in the matrix, which will become the priority initiation sites of microcracks during UV aging and accelerate the crack growth rate. It is suggested to improve the dispersion uniformity by the twin-screw melt blending process.

III. Impact of Color Masterbatches

1. Pigment Selection and Stability

Carbon Black:

Optimal UV shielding performance (absorption rate > 99%)

Potential drawback: High heat absorption may cause localized temperature rise (15-20°C higher than blank samples)

Recommended applications: Dark-colored products and outdoor infrastructure

Organic Pigments (e.g., Phthalocyanine Blue):

Photodegradation tendency: Prone to photo-oxidation in the 380-500 nm wavelength range

Dual hazard: Not only causes fading but also generates degradation byproducts that induce resin chain scission

Titanium Dioxide (TiO₂):

Reflective UV protection: Requires Al₂O₃/SiO₂ double-layer coating (coverage > 90%)

Untreated risk: Surface hydroxyl groups catalyze free radical formation, accelerating material yellowing

2. Critical Concentration Effects

Carbon Black:

0.5-2% addition can reduce UV transmittance to 1/10 of the initial value

Titanium Dioxide:

Minimum effective concentration: 8% (volume fraction)

Insufficient concentration: Discontinuous reflective interfaces lead to UV "hot spots"

IV. Impact of Recycled Materials

Molecular chain degradation

The molecular weight of recycled materials decreased, and the content of free radicals increased due to repeated processing, which made them more vulnerable to UV attack.

Impurities and compatibility

Residual additives (such as old pigments) may react with the new formula to form aging weak points.

When recycled materials from different sources are mixed, poor compatibility will accelerate interface aging.