In everyday production and daily life, PP corrugated sheets are highly favored for their light weight, corrosion resistance, and affordability. However, many users have found that once exposed to the outdoors, these panels tend to become brittle, fade, or even crack, severely shortening their service life.
The culprit behind this lies within the molecular chains of the PP (polypropylene) material—the tertiary carbon atom.
This structure is highly susceptible to the combined effects of outdoor UV radiation, oxygen, and temperature fluctuations, leading to molecular chain breakage and oxidative degradation.
But don’t worry—this problem is not insurmountable. By addressing every stage of the process—from raw materials and production to protective measures during use—we can significantly enhance the material’s weather resistance.
Raw Material Formulation: Dressing the Sheets in “Protective Gear”
The first step is to strengthen the “constitution” of the sheets fundamentally. The key lies in adding anti-aging additives to build a synergistic protection system.
1. Blending Anti-Aging Additives:
This is the most critical measure. It requires a “combination of measures”:
UV absorbers (such as UV-326): These absorb UV light like “sunscreen,” typically used at a concentration of 0.1%–0.5%.
Hindered amine light stabilizers (e.g., Tinuvin 770): When used in combination with UV absorbers, they produce a “1+1>2” effect, improving weather resistance by 3–5 times; the recommended usage is 0.2%–1%.
Primary and secondary antioxidants: A blended system of “primary antioxidant 1010 + secondary antioxidant 168” (total 0.1%–0.3%) effectively inhibits thermal oxidative degradation during processing and use.
2. Strictly control the proportion of recycled material:
Recycled material has extremely poor weather resistance. For outdoor-use sheets, the proportion of recycled material should not exceed 20%.
Furthermore, during use, anti-aging additives equivalent to 50%–80% of the virgin material formulation must be added.
3. Selecting the Optimal Base Resin:
Copolymer PP inherently exhibits better weather resistance than homopolymer PP.
For applications with extremely high performance requirements, blending 5%–10% HDPE or EVA into the PP can effectively enhance UV resistance and impact resistance.
Production Process: Intrinsic Quality Is Key
A good formulation requires a good production process to be realized; otherwise, potential issues may arise during production.
1. Precise Control of Extrusion Temperature:
PP material is temperature-sensitive and degrades very easily at temperatures exceeding 230°C.
The temperature in the homogenization section of the barrel should be controlled between 180–210°C, and the die temperature should be maintained between 200–220°C. Equipment should be cleaned regularly to prevent material buildup and coking.
2. Use Gradient Cooling:
Uneven cooling can lead to concentrated internal stress, making the sheets more prone to cracking when exposed to outdoor conditions. A “gradient cooling” method should be adopted, with the water temperature in the front section of the shaping jacket controlled at 50–60°C and reduced to 20–30°C in the rear section, while ensuring uniform water spray distribution.
3. Optimize Traction Parameters:
The traction speed must be perfectly matched to the extrusion speed, with the draw ratio ideally controlled between 1.1 and 1.3 times.
At the same time, ensure consistent pressure at both ends of the traction rollers to avoid improper molecular chain orientation caused by uneven stretching.
Post-Processing and Use: The Final Protective Barrier
Even with panels of the highest quality, proper post-processing and usage guidelines can significantly extend their outdoor service life.
1. Design Protective Structures:
For transparent or light-colored sheets, a dark light-blocking layer can be laminated onto the surface.
Alternatively, a “core layer + surface layer” composite structure can be used, with the surface layer made from a high-weatherability formulation and the core layer made from recycled material, balancing cost and performance.
2. Standardized Storage and Use:
Storage: Finished sheets must not be stacked outdoors for extended periods.
They should be stored in an indoor warehouse or tightly covered with a shade cloth, and kept away from heat sources.
During Use: Avoid prolonged direct exposure of the sheets to intense sunlight as much as possible.
Direct UV exposure can be reduced by installing awnings or similar measures.
Summary
Addressing the weather resistance of PP corrugated sheets is a systematic process that requires coordination among three key areas: materials, production, and usage:
1. Materials are the foundation: Enhance anti-aging capabilities from the source through a “synergistic protection” additive system.
2. Production is the safeguard: Precise and gentle processing is key to ensuring the intrinsic quality of the panels.
3. Use is the extension: Proper post-production protection and standardized use serve as the final line of defense for extending service life.
By addressing these three key points, we can effectively overcome the challenge of PP corrugated sheets’ “short outdoor lifespan,” enabling them to serve various application scenarios more durably and reliably.