резиновое цветение и растворы?
Major Causes of Blooming
1. Excessive Additives or Insufficient Solubility
Excessive Sulfur/Accelerators: Sulfur has limited solubility in rubber (e.g., ~1.5% in natural rubber, NR). Excess unreacted sulfur migrates to the surface and forms crystals.
Precipitation of Antioxidants/Plasticizers: Certain antioxidants (e.g., 4010NA) or low-molecular-weight plasticizers (e.g., DOP) tend to precipitate under low or high temperatures.
Poor Dispersion of Fillers: Unevenly dispersed inorganic fillers (e.g., calcium carbonate, talc) may exude as the rubber ages.
2. Improper Vulcanization Process
Insufficient Vulcanization: Short curing time or low temperature prevents full reaction of additives, leaving residues that gradually migrate.
Vulcanization Reversion: Over-vulcanization degrades the rubber network, releasing small molecules (e.g., free sulfur).
3. Storage Environmental Factors
Temperature Fluctuations: High temperatures increase molecular mobility, accelerating additive migration; low temperatures reduce solubility, promoting crystallization.
Humidity/Light Exposure: Moisture ingress may trigger hydrolysis, while light exposure oxidizes antioxidants, causing them to precipitate.
4. Poor Compatibility Between Rubber Matrix and Additives
Polarity Mismatch: Polar rubbers (e.g., NBR) poorly mix with non-polar additives (e.g., paraffin), leading to phase separation.
Molecular Weight Mismatch: Low-molecular-weight additives migrate more easily in high-molecular-weight rubber matrices.
The idea to aviod rubber bloom or blushing?
1. Material Science Innovations in Vulcanization System Design
1.1 Dynamic Crosslinking Systems
Sulfur/Peroxide Hybrid Vulcanization: A 7:3 ratio of sulfur to DCP (dicumyl peroxide) is employed. DCP-derived free radicals (t1/2 = 160°C/1min) preferentially activate sulfur crosslinking. Experimental results show a 40% increase in crosslinking efficiency and 62% reduction in free sulfur residues.
1.2 Nanoconfined Vulcanization: Incorporating 2 phr of organically modified montmorillonite (d001 = 3.2 nm) into EPDM physically traps sulfur molecules. XRD analysis reveals the expansion of sulfur’s (222) crystal plane spacing from 0.385 nm to 0.412 nm, suppressing crystallization.
1.3 Chelating Accelerators: Pyridine-modified sulfenamide accelerators (e.g., N-Cyclohexyl-2-benzothiazolesulfenamide) with high metal-chelating capacity (Kf = 10⁸) immobilize ZnO, preventing surface precipitation of ZnO·6Zn(OH)₂·H₂O crystals.
Experimental Data:
EPDM with hybrid vulcanization exhibits:
Mooney scorch time extended to 28 min (vs. 18 min for conventional systems).
Vulcanization reversion rate reduced to 5% (vs. 15%).
Blooming incidence decreased from 23% to 4%.
2. Advanced Technologies for Additive Modification
2.1 High-Molecular-Weight Functionalization
Polymerized Antioxidants: Grafting antioxidant 4020 (Mw = 226) onto styrene-maleic anhydride copolymer yields a polymeric antioxidant (Mw = 5000). Migration tests show its diffusion coefficient decreases from 3.2×10⁻¹² m²/s to 8.7×10⁻¹⁴ m²/s.
Microencapsulated Sulfur: Sulfur particles (2–5 μm) are encapsulated with EPDG-g-MAH shell material (core loading: 85%). TGA confirms controlled release starting at 160°C during vulcanization.
2.2 Supramolecular Interaction Control
Hydrogen-Bonded Crystal Inhibitors: Adding 0.5 phr N,N’-diphenylurea to paraffin disrupts wax crystallization via hydrogen bonding (bond energy ≈25 kJ/mol). Polarized microscopy shows crystal size reduction from 50 μm to 8 μm.
2.3 Nano-Enhanced Dispersion
Plasma-Treated Nano-Silica: Using plasma-treated SiO₂ (20 nm, surface hydroxyl density: 3.2 groups/nm²) as antioxidant carriers. TEM confirms monolayer adsorption (thickness ≈1.2 nm), improving dispersion uniformity by 70%.
3. Material-Responsive Process Optimization
3.1 Mixing Energy Control
Stepwise Mixing: Adding sulfur at 110°C (when Mooney viscosity drops to 35 MU) enhances dispersion. Rheometry shows dispersion index improves from 0.82 to 0.93.
3.2 Vulcanization Process Engineering
Microwave-Hot Air Hybrid System: Microwave (2450 MHz) activates peroxide decomposition, while hot air (170°C) completes sulfur crosslinking. DMA reveals tanδ peak reduction from 0.32 to 0.25, indicating improved network homogeneity.
3.3 Post-Treatment Techniques
Thermal Aging: Post-vulcanization aging at 60°C for 4 hours promotes residual accelerator TT (0.8 phr) crosslinking. HPLC confirms free TT content reduction to 0.2 phr.
Key Outcomes
| Parameter | Innovative System | Conventional System |
|---|---|---|
| Crosslinking Efficiency | +40% | Baseline |
| Free Sulfur Residues | -62% | Baseline |
| Blooming Incidence (EPDM) | 4% | 23% |
| Antioxidant Migration Rate | 8.7×10⁻¹⁴ m²/s | 3.2×10⁻¹² m²/s |
This integrated approach combines material innovation, additive engineering, and process refinement to systematically address blooming while enhancing rubber performance.