4. Footwear Chemicals: From Toxicity Reduction to De-Fossilization
| Dimension | 2021 (5 years ago) | 2026 (Present) | Future Trend (c.2030) |
|---|---|---|---|
| Adhesive Route | Solvent-borne PU glue with high benzene & VOC emissions | Water-based WPU / PUR hot melt, solvent-free system | Self-healing dynamic covalent bio-adhesives with thermally triggered debonding for easy shoe disassembly & recycling |
| Core Environmental Indicators | VOCs >500 g/L; poor hydrolysis resistance | VOCs <50 g/L; peel strength ≥3.5 N/mm matching solvent adhesives | Zero VOC emission; tunable bonding strength enabling controlled degradation at recycling stage |
| Functional Additives | C6/C8 fluorinated water repellents containing PFAS persistent substances | Fluorine-free polymer / silicone waterproof additives | Biomimetic superhydrophobic nano-coatings relying on physical surface structure |
| Raw Material Source | Fully fossil chemical feedstock | Petroleum base + 15%–40% castor oil derived bio-based polyols | CCU captured CO₂ feedstock or 100% bio-based chemical systems |
Part III Precise Physical Property Data & Process Temperature Parameters of Core Raw Materials
1. Supercritical Physical Foaming of PEBA (Blowing-Agent-Free Ultra-Light Midsole)
1) Post-Molding Physical Properties
2) Hardness: 38 Shore C ~ 45 Shore C (balanced cushioning and landing support)
3) Foam Density: 0.09 ~ 0.12 g/cm³
4) Rebound Rate: 78% ~ 85%
5) Tensile Strength: ≥ 2.2 MPa
6) Tear Strength: ≥ 12 N/mm
7) Compression Set (70°C, 22h): ≤ 25% (excellent anti-collapse performance)
Supercritical Injection / Compression Foaming Process Parameters
1) Feed zone: 165°C ~ 175°C
2) Compression zone: 180°C ~ 190°C
3) Metering zone: 195°C ~ 205°C
4) Nozzle: 200°C ~ 210°C
Supercritical fluid injection pressure:
1) N₂ system: 22 MPa ~ 28 MPa
2) CO₂ system: 12 MPa ~ 16 MPa
2. Water-Based Polyurethane Adhesive (WPU / PUD for Upper-Sole Bonding)
1) Adhesive Physical Properties (As Supplied)
2) Appearance: Homogeneous milky white liquid
3) Solid Content: 45% ~ 50%
4) Viscosity (25℃): 2000 ~ 3000 mPa·s (suitable for automatic spraying or manual application)
5) pH Value: 7.0 ~ 9.0 (weakly alkaline)
6) VOCs: <20 g/L (far exceeding EU and China latest environmental standards)
Peel Strength:
1) Initial tack: ≥ 2.0 N/mm
2) Ultimate strength (24h full crosslinking): ≥ 3.8 N/mm (preferred failure mode: substrate tearing instead of adhesive separation)
Production Line Application & Drying Parameters
Part IV Material Performance under Extreme Operating Conditions
1. Extreme Condition Performance of Supercritical Foamed PEBA Midsole
Hydrolysis Resistance Test
2) Hardness variation: ≤ 3 Shore C drop (no obvious softening)
3) Rebound retention: Initial rebound 80%; maintained at 72% ~ 75% after aging, decay rate <10%
4) Volume expansion / shrinkage: ≤ ±1.5% (stable geometry, no demolding or deformation)
-20°C Low-Temperature Brittleness Test
2) No visible cracks after 100,000 flexing; no cell collapse
3) Hardness increment: Only rises from 40 Shore C (ambient) to 44–46 Shore C at -20°C, increase <15%
4) DMA glass transition temperature Tg: -60°C ~ -65°C
5) Conventional EVA suffers >30% hardness surge and severe cracking under subzero conditions; PEBA retains over 85% of ambient cushioning and rebound at extreme low temperatures.
2. Extreme Condition Performance of Water-Based Polyurethane Adhesive (WPU)
Two-component crosslinking forms dense interpenetrating polymer networks (IPN) that effectively prevent sole delamination under humid and cold environments.
Hydrolysis & Humid Aging Test
2) Post-aging peel strength: ≥ 2.5 N/mm (initial strength 3.8 N/mm, retention rate 65%–70%)
Failure characteristic: Formulations based on polycarbonate diol (PCDL) resist water molecule attack; failure occurs via substrate tearing rather than adhesive gelation.
-20°C Dynamic Flex & Cold Delamination Test
2) Low-temperature peel strength rises to ≥ 5.0 N/mm due to polymer chain freezing
3) No edge delamination after 50,000 low-temperature flex cycles
Controlled crystallinity of WPU emulsion ensures limited chain mobility at low temperature to avoid glass-like brittle fracture of adhesive layers.
