Abstract

As the demand for lightweight and environmentally friendly buses increases, the comprehensive performance requirements for interior materials are becoming increasingly stringent. The combination of TPU (Thermoplastic Polyurethane) and ABS (Acrylonitrile Butadiene Styrene copolymer) through co-extrusion technology has emerged as an ideal choice for the new generation of bus interior panels. Jiangsu Compound has developed new product research and development based on existing projects. For this reason, we have customized a machine for the production of TPU/ABS sheets. Its core advantages such as scratch resistance and environmental protection provide theoretical support for its further promotion and application in the field of bus interiors.

 picture.1 New Machine Transportation

1. Requirements for Bus Interior Materials and Compatibility of TPU/ABS

1.1 Diverse Demands for Bus Interior Materials

With the vigorous development of the bus industry, the comfort and safety of interior environments have gained increasing attention. As a major component in the vehicle, interior panels must withstand mechanical stresses from daily passenger contact and luggage handling, while enduring environmental factors like light, temperature, and humidity changes. Key requirements include:

Mechanical Performance: High strength to resist vibrations, impacts, and loads from passengers/luggage, ensuring no deformation or fracture during long-term use. Good fatigue resistance is also critical.

Environmental Adaptability: Excellent weather resistance to UV, ozone, temperature fluctuations, and humidity to prevent yellowing, embrittlement, and fading-especially important for buses operating in high-altitude, strong-sunlight, or extreme-temperature regions.

Usability: Scratch resistance to maintain appearance under frequent friction (e.g., clothing, luggage), and easy cleanability to reduce maintenance costs through simple wiping.

Environmental Standards: Compliance with strict regulations like RoHS and in-vehicle VOC (Volatile Organic Compounds) limits, requiring low hazardous substances and high recyclability.

Lightweight Design: Reduced material weight to lower vehicle energy consumption and improve fuel efficiency.

picture.2   bus interior sheet with texture

1.2 Limitations of Traditional Materials

Pure ABS: Good rigidity and processability but poor surface hardness and weather resistance, prone to scratches and aging.

PVC: Contains plasticizers (non-environmental-friendly), with inadequate scratch/weather resistance and performance degradation over time.

Metal-Clad Materials: Heavy weight (incompatible with lightweight trends), high processing costs, and potential safety risks in collisions.

1.3 Advantages of TPU/ABS Composite System

The co-extruded TPU/ABS system meets all requirements through complementary properties:

Performance Synergy: ABS provides rigid support and processability as the base material, while TPU enhances surface performance with scratch resistance, weather resistance, and environmental friendliness.

Eco-Friendly & Lightweight: TPU is plasticizer-free (compliant with environmental standards) and low-density, reducing panel weight while maintaining performance.

picture.3 Traditional craftsmanship to make soft leather

2. TPU Properties and Their Enhancements for Interior Panels

2.1 Excellent Scratch and Wear Resistance

Material Flexibility: TPU offers a wide Shore hardness range (60A–80D) and low surface friction coefficient, allowing customized hardness for different parts (e.g., high-hardness TPU for frequently rubbed areas like seat panels, and low-hardness TPU for flexible parts like door panel corners).

Data Support: Taber abrasion loss (CS-17 wheel, 1kg load) is only 20–40mg, significantly lower than common plastics (e.g., 80–120mg for pure ABS), ensuring long-term surface integrity under friction (e.g., luggage contact).

2.2 Weather and Aging Resistance

Environmental Durability: TPU resists UV, ozone, and harsh temperature/humidity changes without molecular degradation or discoloration.

Field Performance: In high-altitude/sunny regions (e.g., Tibet, Qinghai), TPU-surfaced panels maintain appearance and performance for years, outlasting traditional materials in accelerated aging tests (withstanding thousands of hours of harsh conditions).

picture.4  Surface treatment of interior panels

2.3 Environmental Friendliness and Easy Cleanability

Green Attributes: TPU is free of heavy metals and plasticizers, compliant with RoHS and 车内 VOC standards, and recyclable.

Cleaning Efficiency: Its dense surface resists oil/stain penetration, enabling quick cleaning with a damp cloth-critical for high-traffic bus interiors.

2.4 Process Compatibility

Matching Melt Temperatures: TPU and ABS share similar melt ranges (180–220°C), enabling seamless co-extrusion without compatibility issues.

Process Flexibility: Adjustable TPU formulations and process parameters meet diverse part requirements.

picture.5 Traditional Technology

3. Key Technologies of TPU/ABS Co-Extrusion Process

3.1 Process Principle

Material Preparation: Dry TPU and ABS to remove moisture, then feed into a twin-screw extruder.

Melting & Plasticizing: Extruders heat both materials to 180–220°C, forming uniform melts.

Co-Extrusion Molding: TPU (surface layer) and ABS (core layer) merge in a custom die to form a "TPU functional layer + ABS support layer" structure, followed by cooling, traction and cutting.

3.2 Process Advantages

Cost Reduction:

Material Savings: ABS accounts for 70–80% of the composite, reducing expensive TPU usage (cost 45% lower than full-TPU injection).

Efficiency Gains: One-step forming eliminates adhesive bonding, reducing,equipment, and labor costs.

Performance Optimization:

Controllable Layer Thickness: TPU layer thickness (0.2–1.0mm) balances function and cost (e.g., thicker layers for high-scratch areas).

Integrated Performance: ABS rigidity + TPU surface properties create panels with superior strength, durability, and environmental compliance.

High Productivity: Continuous, automated production ensures consistency and low scrap rate.

3.3 Technical Challenges & Solutions

Interlayer Adhesion:

Issue: Chemical differences may cause delamination.

Solutions: Adjust melt temperature gradients (TPU slightly hotter than ABS) to promote molecular diffusion; optimize die flow channels for better mixing and interfacial pressure.

Surface Defect Control:

Issue: Temperature fluctuations or impurities cause surface flaws (e.g., melt fracture, bubbles).

Solutions: Use precision temperature control (±1°C tolerance), filter materials to remove impurities, and optimize extrusion/cooling parameters.

picture.6 Extrusion process equipment

4. Practical Applications and Results

4.1 Case 1: Large Bus Manufacturer

Background: Needed scratch/weather resistance and weight reduction for long-haul/tour buses (original ABS panels had rapid aging/scratches).

Solution: 75% ABS core + 0.5mm TPU layer, strict process control.

Results:

Scratch test: 500 cycles (500g steel wool) with no visible damage (vs. 100 cycles for pure ABS).

30% weight reduction vs. metal-clad panels, improving fuel efficiency.

45% cost saving vs. full-TPU injection, with 2+ years of stable performance in harsh environments.

4.2 Case 2: Urban Bus Company

Background: High passenger traffic required extreme scratch resistance, easy cleaning, and low VOC.

Solution: High-scratch TPU surface + high-rigidity ABS core.

Results:

50% faster cleaning with simple wiping, 3+ years of service life (double traditional panels).

VOC levels far below national standards, ensuring passenger health.

picture.7 Roller Embossing Process

5. Future Trends and Prospects

5.1 Expanded Applications

Advanced co-extrusion equipment will enable TPU/ABS composites for more interior parts (dashboard, door handles, seat frames) by adjusting formulations-e.g., heat-resistant TPU for dashboards and wear-resistant TPU for door handles.

5.2 Sustainable Development

Bio-Based TPU: Developed from renewable resources (plant oils, starch) to reduce carbon footprint and meet circular economy goals.

Recycling Systems: Focus on recyclable designs and waste panel reprocessing to promote resource efficiency.

5.3 Intelligent & Functional Innovations

Integration with sensors/conductive materials for smart features (self-healing surfaces, pressure-sensitive dashboards) and functional additives (antibacterial, anti-static properties) to enhance interior quality.

picture.8 Thermal Lamination Process

Conclusion

TPU/ABS co-extrusion technology balances performance, cost, and environmental needs through material and process innovation, offering an efficient solution for bus interior upgrades. Its scratch resistance, long lifespan, and eco-friendliness align perfectly with high-usage public transport scenarios, promising broad market potential. As technology advances, this composite will expand its applications, driving sustainable and intelligent development in the bus industry. Continuous R&D will be key to overcoming new challenges and maximizing its potential.