Material Stability for Automotive Interiors and Cabins

Interior parts are technically harder than exterior parts. The reason is direct: exteriors only need to hold their appearance where it is "visible", while interiors must pass weather resistance, low VOC, low odor, low fogging and flame retardancy - five tests at once, and between these indicators there is a real mutual constraint - for example, some low-molecular-weight additives that enhance weather resistance also increase fogging and odor contributions.

1. The core contradiction of interiors

Interiors are gated by VOC of 50 μg/g or less under VDA 278 and odour of grade 3.0 or less under VDA 270.

2. Tiangang's approach

2.1 Prefer polymeric high-molecular-weight grades to cut migration and fogging contributions

HS-944,HS-950,HS-622) have high molecular weight.

This is the single most important principle for interior parts.Low-molecular-weight HALS (e.g. the UV-770 family, molecular weight about 481) migrate fast and work early, but release amine compounds under sustained high temperature, contributing to fogging and odor; polymeric HALS (e.g.resist extraction and are low in volatility, making them the safer choice against limits such as VDA 278 / DIN 75201.

It should be noted that polymeric products act slightly slower and are weaker in early weather resistance, so in practice the common approach is "a polymeric base + a very small amount of low-molecular-weight surface touch-up" rather than either/or. On loadings, interior parts are typically held at HALS 0.2-0.5% and UVA 0.1-0.3%.

2.2 PVC systems: pay special attention to alkaline-HALS compatibility

Dashboard skins and seat upholstery use large amounts of flexible PVC. During processing and service, PVC continuously releases HCl, while conventional HALS is alkaline - when the two coexist, the HALS is neutralized and consumed by the HCl, and the PVC side also risks bloom or frost from the neutralization products.

Tiangang's approach: in PVC-related systems, give priority to low-alkalinity NOR products that do not react with acidic substances——XT-8 (high-molecular-weight N-OR, resistant to sulfur at 3000-7000 ppm and chlorine at ≤850 ppm) and HS-112 (low-molecular-weight liquid N-OR, whose low alkalinity avoids reaction with acidic components). Compared with conventional alkaline HALS, the N-OR structure stays active in acidic environments.

2.3 Interior-part flame retardancy: GB 8410 is a hard threshold

GB 8410-2006 requires a horizontal burning rate ≤100 mm/min, a mandatory test item; the US market counterpart is FMVSS 302 (≤102 mm/min). For polymers, the usual route is to introduce flame retardants or flame-retardant copolymers, and on parts requiring both flame retardancy and weather resistance (e.g. airbag covers, some interior frames), FR-810A the "flame retardancy + light stabilization + long-term thermal stability" three-effects-in-one is the more convenient solution.

3. Quick reference by part

For more parts and recommended loadings, see ⑤ Selection Guide & Product Matrix. To discuss a formulation for a specific interior part, feel free to contact us.