How To Manufacture Memory Foam?

Formulation Composition
Memory foam, also known as memory foam, derives its unique properties from a precisely designed chemical formulation. The core component is polyether polyol, which forms the basic skeleton of the foam. Polyether polyols with different molecular weights and hydroxyl values give the foam various physical properties: high hydroxyl values improve hardness and load-bearing capacity, while high molecular weights enhance softness and resilience. Typically, polyether polyols with molecular weights between 3000 and 6000 are most commonly used, with specific selections made based on product requirements.

Isocyanates are key reactants in the foam polymerization process, reacting with polyether polyols to form polyurethane structures. Toluene diisocyanate (TDI) is often used to make soft and breathable foams due to its high reactivity, though its volatility poses environmental and health risks. In contrast, methylene diphenyl diisocyanate (MDI) has lower reactivity but offers better aging resistance, mechanical strength, and lower toxicity. In practice, blends of TDI and MDI or modified MDI are often used to strike a balance between performance and safety.

Catalysts play a critical role in the foaming process. Stannous octoate is a commonly used organotin catalyst that efficiently accelerates the reaction between polyether polyols and isocyanates, allowing better control of the foaming process. Additionally, amine catalysts such as triethylamine are often used in combination with stannous octoate to further fine-tune the reaction rate and final foam properties.

The pore structure of the foam depends on the foaming agents used. Water is a common chemical blowing agent that reacts with isocyanates to produce carbon dioxide gas. Another common chemical foaming agent is azodicarbonamide (ADCA), which decomposes under heat to generate nitrogen gas. Physical foaming agents such as hydrocarbons (e.g., pentane) may also be used; they vaporize under heat to form bubbles, reducing foam density and enhancing softness and breathability. It's important to note that older foaming agents like chlorofluorocarbons (CFCs) have been phased out due to their ozone-depleting effects.

To optimize the overall foam performance, multiple additives are incorporated. Silicone-based surfactants effectively reduce the surface tension of the mixture, promoting uniform bubble formation and preventing cell rupture or coalescence, thereby ensuring fine and even foam structure. Antioxidants like butylated hydroxytoluene (BHT) delay yellowing and hardening caused by oxidation during use, extending product life. UV absorbers, such as benzophenone compounds, absorb harmful ultraviolet rays, significantly enhancing light aging resistance.

Typical Reference Formulation (Parts by Weight):
The following is a reference formulation for memory foam and can be adjusted as needed:

Polyether polyol (e.g., 330N): 100 parts

Isocyanate: 40–50 parts

Stannous octoate (catalyst): 0.5–1 part

Triethylamine (catalyst): 0.3–0.8 parts

Water (blowing agent): 3–5 parts

ADCA (blowing agent): 0.5–1 part

Silicone oil (surfactant): 1–2 parts

BHT (antioxidant): 0.2–0.5 parts

Benzophenone compound (UV absorber): 0.1–0.3 parts

Please note that raw materials from different suppliers may vary in performance. Optimal dosages must be determined through experimentation. Additionally, factors such as ambient temperature and humidity can influence the reaction process, potentially requiring slight adjustments in catalyst amounts to ensure smooth foaming and stable product properties.

Manufacturing Process
The production of memory foam typically involves the following main steps:

Raw Material Metering and Premixing: Precisely weigh polyether polyols, isocyanates, catalysts, blowing agents, and additives according to the formulation, and carry out initial mixing.

High-Speed Mixing and Reaction: Transfer the pre-mixed materials into a high-speed mixing machine to ensure thorough blending and initiate the polyurethane polymerization reaction.

Mold Foaming and Shaping: Quickly pour the mixture into pre-set molds. Under controlled temperature and humidity conditions, the chemical reaction continues, expanding the material to fill the mold and form foam blanks with defined shapes and sizes.

Curing and Aging: Let the foamed blanks rest at room temperature or slightly elevated temperatures for a period, allowing the polyurethane network to further crosslink and solidify, enhancing mechanical properties.

Post-Processing: Cut and trim the cured foam to meet final product specifications. Depending on product requirements, surface treatments such as moisture-proof or flame-retardant coatings may be applied to add extra functionalities.