How to Reduce Odor and VOC Emissions of Automotive Rubber Products

Introduction

Against the backdrop of stringent standards for automotive NVH and indoor air quality, rubber components are no longer limited to sealing and vibration damping functions. As vehicle OEMs elevate the monitoring of in-cabin gas safety (VDA 270 odor grading and total VOC content) to a core evaluation index, rubber parts with high volatile emissions and pungent odors are being phased out comprehensively.

The intrinsic odor of rubber products essentially stems from the thermodynamic escape of low-molecular-weight volatiles under specific temperatures. To achieve low odor and low VOC performance, a three-in-one systematic engineering approach must be adopted: blocking volatile substances at the molecular source, modifying crosslinking networks, and implementing thermal dynamic post-treatment to minimize emissions to the greatest extent.

I. Purification of Raw Rubber Matrix and Plasticizers at the Molecular Source

Rubber base materials and process oils account for over 70% of the total formula volume, serving as the primary source of VOC emissions.

Elimination of Residual Third Monomers (ENB Residuals)

During the synthesis of conventional Ethylene Propylene Diene Monomer (EPDM) rubber, incompletely reacted third monomers (e.g., Ethylidene Norbornene, ENB) remain trapped within polymer clusters. These substances produce a strong acidic kerosene-like volatile odor.

Technical Solution

Fully phase out conventional Ziegler-Natta catalyzed raw rubber and switch entirely to metallocene-catalyzed EPDM (mEPDM). Metallocene catalysts feature ultra-high reaction activity and an extremely narrow Molecular Weight Distribution (MWD), fundamentally eliminating low-molecular-weight oligomers and residual monomers.

Alkane Purification of Lubrication Systems

Low-grade conventional process oils contain abundant heterocyclic compounds and short-chain hydrocarbons, which readily vaporize under vehicle exposure at 60–70°C.

Technical Solutions

1. Permanently ban all high-aromatic oils; only use high-purity hydrogenated paraffin oils with a flash point above 230°C.

2. For oil-resistant Nitrile Butadiene Rubber (NBR), replace highly volatile phthalate plasticizers (DOP/DBP) with high-molecular-weight non-volatile polyester plasticizers or composite Dioctyl Terephthalate (DOTP).

II. Crosslinking Network Reconstruction: Block Thermal Cracking Pathways of Small Additive Molecules

Traditional vulcanizing agents and accelerators undergo secondary thermal cracking at vulcanization temperatures of 150–180°C, releasing large volumes of foul-smelling amine-based gases.

Eliminate Secondary Amine Emission Sources

Failure Mechanism

Classic accelerators including TMTD (Thiuram Disulfide) and BZ (Zinc Dibutyldithiocarbamate) break chemical bonds during crosslinking, releasing dimethylamine and dibutylamine. These compounds are the primary culprits behind the fishy odor and excessive VOC levels detected inside vehicles.

Replacement Matrix

1. Adopt sulfenamide accelerators (e.g., NS, CZ) as the primary vulcanization system.

2. When thiuram reinforcement is required, exclusively use TBzTD (Tetrabenzylthiuram Disulfide). TBzTD decomposes into benzylamine, a high-molecular-weight, high-melting-point compound with zero volatility, delivering a dramatic improvement in odor grading.

Lattice Trapping: Add Nano Capture Agents

At the final stage of crosslinking network formation, incorporate 1.5%–3.0% ultra-fine porous modified zeolite molecular sieves or dedicated chemical adsorbents.

Mechanism

Uniform nano-scale pore channels in molecular sieves form strong physical adsorption potential wells within the crystal lattice, permanently trapping trace residual odor molecules generated during vulcanization and blocking their volatilization pathways.

III. Dynamic Post-Treatment: Vacuum and Thermal Stress Relief Before Delivery

Even with fully optimized formulas, trace free volatiles remain embedded deep within crosslinking networks. End-stage processes are required for ultimate volatile removal.

Purification Process for Finished Products

Vulcanized finished parts → Mechanical trimming → Recirculating hot air oven treatment (130°C, 3 hours) → Ultrasonic weak alkaline cleaning → Surface micropore sealing via polymer coating

Post-Curing Thermal Desorption in Ovens

This is currently the most effective and industrially feasible physical method to reduce odor in automotive rubber components.

Process Specifications

Feed molded products (brake pedal covers, wall grommets, air conditioning ducts, etc.) into forced recirculating hot air ovens and bake continuously at 120–140°C for 2 to 4 hours.

Working Principle

Long-duration artificial high-temperature thermal stress simulates extreme sunlight exposure conditions, forcing deep-seated low-molecular-weight volatiles inside rubber parts to release completely prior to shipment. Volatiles are then extracted and exhausted via the oven ventilation system.

Surface Barrier Coating Technology

For parts directly exposed to air intake systems, such as wiper blades and window guide channels, apply a micron-thick water-based polyurethane or functional silicone film coating during post-processing.

Working Principle

This dense rigid polymer film not only reduces surface friction significantly but also forms an impenetrable physical barrier on rubber micropores, fundamentally blocking the outward escape of odor molecules.

Comparison of Technical Parameters for High-Standard VOC Control