PVC Profile Durability — TiO2 Selection for 15-Year Service

Outdoor PVC applications — window frames, siding, fencing, deck boards — demand exceptional photostability. The PVC polymer itself is photochemically vulnerable; without proper TiO2 + UV stabilizer protection, PVC turns yellow, chalks, and embrittles within 1–3 years of outdoor exposure.

Modern PVC profiles routinely achieve 15–25 year service life. This isn't accidental — it's the result of careful TiO2 selection, dosage optimization, and UV stabilizer formulation.

TiO2 selection criteria for outdoor PVC: 1. Process route: chloride only. Sulfate process has too broad PSD and too much metallic impurity for premium outdoor service. 2. Surface treatment: must include zirconia or heavy silica overcoat. The zirconia layer is essential to suppress photocatalytic degradation of the PVC polymer at the pigment surface. 3. PVC stabilizer compatibility: the TiO2 surface treatment must not antagonize the Ca/Zn or Sn stabilizer system. Some heavy alumina coatings have caused stabilizer issues — qualify carefully.

Recommended SEMITI grades: - SEMITI 2160 — direct Kronos 2160 alternative, standard 10–15 year outdoor PVC - SEMITI 2190 — premium 15–20 year outdoor PVC, slightly higher cost - SEMITI 996 — acceptable for 3–5 year outdoor or indoor PVC only

Dosage levels: - Window frame profile: 4–6 phr (parts per hundred resin) - Siding/cladding: 3–5 phr (often co-extruded with higher-TiO2 capstock over standard core) - Fence boards / decking: 4–6 phr - Indoor PVC pipe/profile: 2–4 phr

Why dosage matters for durability: TiO2 in PVC serves two functions: opacity (cosmetic) and UV protection (durability). For premium outdoor service, you need both: - Below 3 phr: insufficient UV protection for 10+ year service - 4–6 phr: typical premium range, balances cost and durability - Above 7 phr: diminishing returns; PVC mechanical properties begin to suffer

UV absorber package — equally important: TiO2 alone is not enough for premium outdoor PVC. The formulation needs additional UV protection: - HALS (hindered amine light stabilizer): 0.1–0.3% for premium grades. Avoid traditional HALS with aminocompatible TiO2 issues; use modern NOR-HALS for better compatibility. - UV absorber (UV-326, UV-329, UV-360): 0.05–0.1% for premium grades. Absorbs UV before it reaches the polymer. - The HALS + UV absorber combination is synergistic — both together perform much better than either alone.

Capstock vs full-thickness pigmentation: Modern premium PVC profile increasingly uses co-extrusion: a thin (0.3–0.8 mm) "capstock" layer of higher-TiO2 PVC over a thicker (3–6 mm) standard PVC core. The capstock provides outdoor durability; the core is cost-optimized. - Capstock recipe: 5–7 phr SEMITI 2190 + full HALS package - Core recipe: 2–4 phr SEMITI 996 + minimal stabilizer

This approach delivers premium 20-year service at significantly lower total cost than full-thickness pigmentation.

Common failure modes: 1. Using interior-grade rutile (SEMITI 996, 902) in outdoor PVC — visible yellowing within 18 months 2. Insufficient HALS package — pigment alone can't protect PVC at premium service levels 3. Mixing sulfate rutile in outdoor PVC — broader PSD and impurity carry-through cause uneven aging 4. Lead-stabilized PVC (now regulated out in most markets) — the Pb migrates and discolors the surface independently of TiO2

For new product development, validate with 2000+ hr QUV-A exposure plus 1-year Florida natural weathering before committing to a formulation. Accelerated testing alone is not reliable for premium 15-year claims.