Long-Term Stability of Polyurethane Foam with DC-193: A Comprehensive Investigation
Abstract:
This study investigates the long-term stability of polyurethane (PU) foam formulated with DC-193, a commercially available silicone surfactant. PU foams are widely employed in various applications, necessitating a comprehensive understanding of their durability and resistance to degradation over extended periods. The research focuses on assessing the influence of DC-193 concentration on key performance characteristics, including mechanical properties, thermal stability, dimensional stability, and resistance to environmental factors such as humidity and UV radiation. Accelerated aging tests were conducted to simulate long-term exposure, and the resulting changes in foam properties were meticulously analyzed. The findings provide valuable insights into the long-term performance of PU foam modified with DC-193, aiding in the selection of optimal formulations for specific applications.
1. Introduction
Polyurethane (PU) foams are ubiquitous materials utilized across a diverse range of industries, including construction, automotive, furniture, and packaging. Their versatility stems from their tunable properties, such as density, stiffness, and thermal insulation, achievable through variations in the chemical composition and processing parameters. These properties make PU foams ideal for applications requiring cushioning, insulation, and structural support.
The long-term stability of PU foam is a critical consideration for its successful deployment in demanding environments. Degradation mechanisms, including hydrolysis, oxidation, and UV-induced chain scission, can significantly compromise the foam’s performance over time. These mechanisms are influenced by factors such as temperature, humidity, exposure to ultraviolet radiation, and the presence of chemical agents.
The incorporation of additives, such as surfactants, plays a crucial role in controlling the foam’s structure and properties. Silicone surfactants are commonly employed to stabilize the foam during processing, reduce surface tension, and control cell size. DC-193, a commercially available silicone surfactant, is widely used in PU foam formulations. However, its impact on the long-term stability of the foam remains an area of ongoing research.
This study aims to investigate the long-term stability of PU foam formulated with DC-193. The research will focus on evaluating the influence of DC-193 concentration on key performance characteristics, including mechanical properties, thermal stability, dimensional stability, and resistance to environmental factors. The results will provide valuable insights into the selection of optimal formulations for specific applications, ensuring the long-term performance and reliability of PU foam products.
2. Literature Review
The long-term stability of PU foam has been the subject of extensive research. Several studies have investigated the effects of environmental factors on the degradation of PU foams.
2.1 Degradation Mechanisms of PU Foam
- Hydrolysis: Water molecules can react with the urethane linkages in the PU polymer chain, leading to chain scission and the formation of polyols and amines. This process is accelerated at elevated temperatures and high humidity levels. (Grassie & Roche, 1968; Allen et al., 1991)
- Oxidation: Exposure to oxygen can lead to the oxidation of the PU polymer chain, particularly at unsaturated sites. This process can result in chain scission, crosslinking, and discoloration. (Tocker, 1961; Billingham & Calvert, 1980)
- UV Degradation: Ultraviolet radiation can induce chain scission and crosslinking in the PU polymer chain. This process is particularly pronounced at the surface of the foam and can lead to embrittlement and discoloration. (Davis & Sims, 1983; Rabek, 1995)
- Thermal Degradation: Elevated temperatures can cause the PU polymer chain to decompose, leading to the release of volatile organic compounds (VOCs) and a reduction in mechanical properties. (Conley, 1970; Ballistreri et al., 1981)
2.2 Influence of Additives on PU Foam Stability
- Antioxidants: Antioxidants can inhibit the oxidation of the PU polymer chain, thereby extending the foam’s lifetime. (Pospíšil, 2010)
- UV Stabilizers: UV stabilizers can absorb or reflect ultraviolet radiation, thereby protecting the PU polymer chain from UV-induced degradation. (Ranby & Rabek, 1975)
- Flame Retardants: Flame retardants can improve the fire resistance of PU foam, but some flame retardants can also accelerate the degradation of the foam. (Weil & Levchik, 2009)
- Surfactants: Surfactants, such as silicone surfactants, are essential for controlling the foam’s structure and properties. However, the type and concentration of surfactant can also influence the foam’s long-term stability. (Owen, 1981; Hill, 1995)
2.3 Role of DC-193 in PU Foam Properties
DC-193 is a silicone surfactant widely used in the production of flexible PU foams. It is known to influence cell size, cell openness, and overall foam stability during the foaming process. However, the long-term effects of DC-193 on the degradation of PU foams are not fully understood. Some studies suggest that certain silicone surfactants can enhance the hydrolytic stability of PU foams, while others indicate a potential for accelerated degradation under specific conditions. (Kendall, 1986; Rossmy et al., 1979)
3. Materials and Methods
3.1 Materials
The following materials were used in this study:
- Polyol: A commercially available polyether polyol (molecular weight approximately 3000 g/mol).
- Isocyanate: A polymeric methylene diphenyl diisocyanate (pMDI) with an NCO content of 31.5%.
- Water: Distilled water was used as the blowing agent.
- Amine Catalyst: A tertiary amine catalyst (DABCO 33-LV) was used to accelerate the reaction between the polyol and isocyanate.
- Tin Catalyst: A stannous octoate catalyst was used to promote the gelling reaction.
- Surfactant: DC-193, a silicone surfactant.
3.2 Foam Preparation
PU foam samples were prepared using a one-shot process. The polyol, water, catalysts, and surfactant were mixed thoroughly in a beaker. The isocyanate was then added, and the mixture was stirred vigorously for a few seconds before being poured into an open mold. The foam was allowed to rise and cure at room temperature for 24 hours.
Five different foam formulations were prepared, with varying concentrations of DC-193:
- Formulation 1 (Control): 0.0 phr (parts per hundred polyol) DC-193
- Formulation 2: 0.5 phr DC-193
- Formulation 3: 1.0 phr DC-193
- Formulation 4: 1.5 phr DC-193
- Formulation 5: 2.0 phr DC-193
The other components were kept constant across all formulations. The specific formulation is detailed in Table 1.
Table 1: PU Foam Formulations
| Component | Unit | Formulation 1 (Control) | Formulation 2 | Formulation 3 | Formulation 4 | Formulation 5 |
|---|---|---|---|---|---|---|
| Polyol | phr | 100 | 100 | 100 | 100 | 100 |
| pMDI | phr | Calculated based on OH # | Calculated | Calculated | Calculated | Calculated |
| Water | phr | 4.0 | 4.0 | 4.0 | 4.0 | 4.0 |
| DABCO 33-LV | phr | 0.2 | 0.2 | 0.2 | 0.2 | 0.2 |
| Stannous Octoate | phr | 0.1 | 0.1 | 0.1 | 0.1 | 0.1 |
| DC-193 | phr | 0.0 | 0.5 | 1.0 | 1.5 | 2.0 |
Note: pMDI amount was calculated to achieve an index of 110.
3.3 Characterization
The following properties were measured for each foam formulation:
- Density: Measured according to ASTM D3574.
- Tensile Strength and Elongation: Measured according to ASTM D3574 using a universal testing machine.
- Compression Set: Measured according to ASTM D395 after 50% compression for 22 hours at 70°C.
- Thermal Stability: Thermogravimetric analysis (TGA) was performed to assess the thermal decomposition behavior of the foams. Samples were heated from 25°C to 800°C at a rate of 10°C/min under a nitrogen atmosphere.
- Dimensional Stability: Measured according to ASTM D2126 after exposure to elevated temperature (70°C) and humidity (95% RH) for 7 days. The change in volume was recorded.
- Hydrolytic Stability: Samples were immersed in distilled water at 70°C for 7 days. The change in weight and tensile strength were recorded.
- UV Resistance: Samples were exposed to UV radiation (340 nm) for 500 hours using a UV weathering tester. The change in color and tensile strength were recorded.
- Cell Structure: Scanning electron microscopy (SEM) was used to examine the cell structure of the foams.
3.4 Accelerated Aging
Accelerated aging tests were conducted to simulate long-term exposure to environmental factors. The following aging conditions were used:
- Elevated Temperature: 70°C
- High Humidity: 70°C and 95% RH
- UV Exposure: UV radiation (340 nm) for 500 hours.
Samples were aged for 1, 2, 4, 8, and 12 weeks. After each aging period, the foam properties were measured as described above.
4. Results and Discussion
4.1 Initial Foam Properties
The initial properties of the PU foam samples are summarized in Table 2.
Table 2: Initial Properties of PU Foam Samples
| Property | Unit | Formulation 1 (Control) | Formulation 2 | Formulation 3 | Formulation 4 | Formulation 5 |
|---|---|---|---|---|---|---|
| Density | kg/m³ | 30 | 31 | 32 | 33 | 34 |
| Tensile Strength | kPa | 150 | 160 | 170 | 165 | 155 |
| Elongation | % | 120 | 130 | 140 | 135 | 125 |
| Compression Set | % | 15 | 13 | 12 | 14 | 16 |
The results indicate that the addition of DC-193 generally improves the mechanical properties of the PU foam. The tensile strength and elongation increase with increasing DC-193 concentration up to 1.0 phr, suggesting that the surfactant promotes better cell structure and improved polymer chain entanglement. However, at higher concentrations (1.5 and 2.0 phr), the tensile strength and elongation decrease slightly, potentially due to the formation of larger, less uniform cells. The compression set generally decreases with increasing DC-193 concentration up to 1.0 phr, indicating improved resilience and resistance to permanent deformation.
4.2 Thermal Stability
TGA results showed that the initial degradation temperature (Tonset) and the temperature at which 50% weight loss occurred (T50%) were similar for all formulations. This suggests that the addition of DC-193 does not significantly affect the inherent thermal stability of the PU polymer. Detailed TGA data are presented in Table 3.
Table 3: TGA Results
| Formulation | Tonset (°C) | T50% (°C) |
|---|---|---|
| Formulation 1 (Control) | 275 | 340 |
| Formulation 2 | 270 | 338 |
| Formulation 3 | 272 | 342 |
| Formulation 4 | 268 | 335 |
| Formulation 5 | 273 | 341 |
4.3 Dimensional Stability
The dimensional stability of the PU foam samples was assessed after exposure to elevated temperature and humidity for 7 days. The results are shown in Table 4.
Table 4: Dimensional Stability Results
| Formulation | Volume Change (%) |
|---|---|
| Formulation 1 (Control) | 3.0 |
| Formulation 2 | 2.5 |
| Formulation 3 | 2.0 |
| Formulation 4 | 2.3 |
| Formulation 5 | 2.8 |
The results indicate that the addition of DC-193 improves the dimensional stability of the PU foam. The volume change decreases with increasing DC-193 concentration up to 1.0 phr, suggesting that the surfactant helps to stabilize the foam structure and reduce shrinkage or expansion under humid conditions.
4.4 Hydrolytic Stability
The hydrolytic stability of the PU foam samples was assessed after immersion in distilled water at 70°C for 7 days. The results are shown in Table 5.
Table 5: Hydrolytic Stability Results
| Formulation | Weight Change (%) | Tensile Strength Retention (%) |
|---|---|---|
| Formulation 1 (Control) | 5.0 | 70 |
| Formulation 2 | 4.5 | 75 |
| Formulation 3 | 4.0 | 80 |
| Formulation 4 | 4.3 | 78 |
| Formulation 5 | 4.8 | 73 |
The results indicate that the addition of DC-193 improves the hydrolytic stability of the PU foam. The weight change decreases and the tensile strength retention increases with increasing DC-193 concentration up to 1.0 phr, suggesting that the surfactant helps to protect the PU polymer from hydrolysis.
4.5 UV Resistance
The UV resistance of the PU foam samples was assessed after exposure to UV radiation for 500 hours. The results are shown in Table 6.
Table 6: UV Resistance Results
| Formulation | Color Change (ΔE) | Tensile Strength Retention (%) |
|---|---|---|
| Formulation 1 (Control) | 8.0 | 60 |
| Formulation 2 | 7.0 | 65 |
| Formulation 3 | 6.5 | 70 |
| Formulation 4 | 6.8 | 68 |
| Formulation 5 | 7.5 | 63 |
The results indicate that the addition of DC-193 improves the UV resistance of the PU foam. The color change decreases and the tensile strength retention increases with increasing DC-193 concentration up to 1.0 phr, suggesting that the surfactant helps to protect the PU polymer from UV-induced degradation. The color change (ΔE) was calculated using the CIELAB color difference formula.
4.6 Aged Sample Properties
Analysis of the aged samples under all three accelerated aging conditions (elevated temperature, high humidity, and UV exposure) consistently revealed that Formulation 3 (1.0 phr DC-193) generally exhibited the best performance in terms of mechanical property retention (tensile strength, elongation) and dimensional stability. While the control sample (Formulation 1) showed the most significant degradation over time, the samples with higher DC-193 concentrations (Formulations 4 and 5) also exhibited a slight decrease in performance compared to Formulation 3, particularly after longer aging periods. This suggests that an optimal concentration of DC-193 exists for maximizing long-term stability.
4.7 Cell Structure Analysis
SEM analysis revealed that the addition of DC-193 resulted in a more uniform and finer cell structure compared to the control sample. Formulation 3 (1.0 phr DC-193) exhibited the most consistent and well-defined cell structure. At higher concentrations of DC-193 (Formulations 4 and 5), some cell collapse and irregularities were observed, which could contribute to the slight decrease in mechanical properties after aging.
5. Conclusion
This study investigated the long-term stability of PU foam formulated with DC-193. The results indicate that the addition of DC-193 can improve the mechanical properties, dimensional stability, hydrolytic stability, and UV resistance of PU foam. However, the concentration of DC-193 must be carefully optimized to achieve the best long-term performance. An optimal concentration of 1.0 phr DC-193 was found to provide the best balance of properties. Higher concentrations of DC-193 may lead to cell collapse and a reduction in mechanical properties after aging.
The findings of this study provide valuable insights into the selection of optimal formulations for PU foam products requiring long-term durability and resistance to environmental factors. Future research should focus on investigating the effects of other additives and processing parameters on the long-term stability of PU foam. Furthermore, studies on the migration and potential leaching of DC-193 from the foam matrix over time would provide a more comprehensive understanding of its long-term environmental impact. ⚙️
6. References
Allen, N. S., Edge, M., & Ortega, A. (1991). Photodegradation and stabilisation of polyurethanes. Polymer Degradation and Stability, 32(1), 1-25.
Ballistreri, A., Foti, S., Giuffrida, M., Montaudo, G., & Scamporrino, E. (1981). Thermal degradation of polyurethane elastomers. Polymer, 22(4), 471-478.
Billingham, N. C., & Calvert, P. D. (1980). Oxidation of polymers. In Developments in Polymer Stabilisation (Vol. 3, pp. 139-221). Applied Science Publishers.
Conley, R. T. (1970). Thermal stability of polymers. Marcel Dekker.
Davis, A., & Sims, D. (1983). Weathering of polymers. Applied Science Publishers.
Grassie, N., & Roche, R. S. (1968). The thermal degradation of polyurethanes. Part 1. The degradation of a polyetherurethane. Die Makromolekulare Chemie, 112(1), 16-32.
Hill, L. W. (1995). Chemistry and properties of waterborne polyurethanes. Progress in Organic Coatings, 26(3), 163-212.
Kendall, R. S. (1986). Silicone surfactants. Journal of the American Oil Chemists’ Society, 63(8), 1058-1063.
Owen, M. J. (1981). Surface active properties of silicones. In Silicon Based Polymer Science (pp. 705-739). American Chemical Society.
Pospíšil, J. (2010). Antioxidants in science, technology, medicine and nutrition. John Wiley & Sons.
Rabek, J. F. (1995). Polymer photodegradation: mechanisms and experimental methods. Springer Science & Business Media.
Ranby, B., & Rabek, J. F. (1975). Photodegradation, photo-oxidation and photostabilization of polymers: principles and applications. John Wiley & Sons.
Rossmy, G., Lidy, W., Kluth, H., Mach, H. J., & Dhein, R. (1979). Influence of surfactants on the formation of flexible polyurethane foams. Journal of Cellular Plastics, 15(6), 353-362.
Tocker, S. (1961). The thermal oxidation of polyurethanes. Journal of the American Chemical Society, 83(13), 2929-2933.
Weil, E. D., & Levchik, S. V. (2009). Flame retardants in commercial use or development. John Wiley & Sons.
