Kabond Foam, Heshan (2026)

26/05/2026

Why Does Flexible PU Foam Cell Structure Vary So Much?

In the production of flexible polyurethane (PU) foam, cell structure has always been one of the core factors determining product quality. Whether it is comfort, rebound performance, breathability, or long-term stability in use, all of these characteristics are closely related to how the microscopic cells inside the foam are formed.

In many cases, such differences are simply attributed to formulation or equipment. However, if we trace the process back to an earlier stage, the true source of variation often appears at the very moment when foam cells are first “born,” namely the nucleation stage.

In most flexible PU foam systems, the primary source of gas is carbon dioxide generated by the reaction between water and isocyanate. As the reaction proceeds, increasing amounts of CO₂ are produced and dissolved in the polyol system. When the amount of dissolved gas exceeds what the system can stably accommodate under the given conditions, the system enters an unstable state.

In simple terms, there is “too much gas” trapped in the system, and it must be released in the form of bubbles. However, gas does not automatically or uniformly transform into stable foam cells, because the formation of a bubble itself must overcome an interfacial energy barrier.

During the initial nucleation stage, extremely small gas aggregates continuously appear in the system, but only a portion of them can survive and continue to grow. This is because the smaller the bubble, the stronger the effect of surface tension acting on it, making it more likely to be compressed and re-dissolved into the liquid phase.

Only when a bubble grows beyond a certain size can it escape this unfavorable condition and enter a stage of sustained growth. For flexible PU foam production, the key issue at this stage is therefore not simply whether bubbles appear, but how many of them are able to survive and participate in the subsequent formation of the cellular structure.

For this reason, industrial production rarely relies on random gas aggregation to achieve nucleation. Instead, nucleation is actively guided by processing conditions. During mixing, strong shear and turbulence inevitably entrain air and break it into a large number of microscopic bubbles. These microbubbles effectively act as pre-existing nucleation sites, making it much easier for gas to evolve and grow at these locations.

The greater the number of nucleation sites and the more uniform their distribution, the higher the density of initial bubbles, and the finer and more stable the resulting cell structure. From the perspective of the finished product, this usually translates into more uniform feel, more consistent rebound behavior, and a lower risk of coarse cells or bubble coalescence.

Of course, this guidance cannot be intensified without limit. Excessive shear, if not matched with timely structure formation, can also lead to cell instability. Nucleation must always be coordinated with the overall reaction kinetics of the system.

In this process, the role of surfactants cannot be overlooked. In flexible PU foam systems, foam stabilizers do far more than influence the visual appearance of cells.

They directly participate in stabilizing the nucleation stage. A suitable surfactant system can reduce the difficulty of forming gas–liquid interfaces, improve the survival rate of newly formed bubbles, and provide early-stage interfacial support, thereby reducing the likelihood of coalescence and collapse.

This is why, even when other conditions remain unchanged, adjusting the foam stabilizer system alone can lead to significant differences in cell structure.

As the reaction continues, the system temperature gradually rises due to the exothermic nature of polyurethane reactions. With increasing temperature, gas evolution and bubble growth are both accelerated. If the temperature rises too quickly in the early stage, bubbles may form faster than the system can establish sufficient structural strength, leading to non-uniform cell distribution.

If the reaction proceeds too slowly, nucleation may be insufficient, resulting in a low cell density. In practical production, the coordination between nucleation, bubble growth, and gelation is often far more important than any single parameter taken in isolation.

It should be emphasized that nucleation is not the only factor determining final cell structure, but it defines the quality of the starting point. In flexible PU foam, nucleation density affects cell fineness, nucleation stability influences structural uniformity, and nucleation controllability directly determines how wide the usable processing window will be.

Truly stable and reproducible foam quality is built upon a clear understanding and rational control of the nucleation process. This is the fundamental logic that allows flexible PU foam to progress from merely “foaming successfully” to achieving stable production and comfortable, reliable performance in use.

21/05/2026

How Do Manufacturing Processes Determine the Performance Limits of High-Resilience Foam?

Soft and cushiony to sit on yet able to rebound quickly, staying supportive after long periods without collapsing while remaining breathable—high-resilience foam has long become a core material in premium furniture, automotive seats, and medical supports.

As the “performance powerhouse” in the polyurethane family, its outstanding behavior is no accident: from raw-material ratios to molding and curing, every process step precisely regulates its molecular network and cell structure.

Today, let’s dig into the logic behind it and understand the strong correlation between process and performance!

Raw-Material Ratios:
Performance’s “Innate Genetics”—Tiny Differences, Huge Consequences

The core raw materials of high-resilience foam are polyether polyols and isocyanates (commonly a blend of TDI and polymeric MDI), along with additives such as crosslinkers, blowing agent (water), catalysts, silicone surfactants, and others. Different ratios directly determine the “ceiling” of the foam’s final performance.

Polyether polyols: Choosing the right reactivity is key. High-activity polyether must be used; a common choice is grafted polyether (often called “polymer polyol” or POP).

This type of polyol can form stiffer segments, providing strong support. If ordinary polyols or polyols with insufficient activity are used, the foam’s resilience and fatigue resistance will be greatly reduced.

Isocyanate index: The precision art of calculation. The dosage of isocyanate is by no means a simple proportion; it is precisely calculated through the isocyanate index. This index is the ratio of the actual dosage to the theoretical dosage required for complete reaction.

For high-resilience foam, this index is typically controlled between 105–115. If the index is too low, the reaction is incomplete and the foam becomes soft, weak, and easily deformed; if the index is too high, excessive crosslinking occurs, making the foam hard and brittle and even causing cracking.

Additive tuning: The “perfumers” who fine-tune the feel.

Crosslinkers (e.g., trimethylolpropane): A small addition (typically 0.5–3 parts per 100 parts of polyether) can significantly enhance the stability of the molecular network and improve load-bearing capacity and rebound. Too much, however, will make the foam overly hard.

Catalysts: A combination of amine catalysts and organotin catalysts is generally used to balance the “blowing reaction” and the “gelling reaction,” ensuring the foam rises smoothly and then solidifies quickly to form uniform, fine cells.

Silicone surfactants (surface-active agents): They are the “architects” of the cells, stabilizing cell walls and controlling cell size and open-cell rate, which are crucial to the final rebound speed and breathability.

Foaming And Molding:

The “Shaper” Of Cell Structure That Determines Rebound And Breathability

Foaming is the magical moment when foam transforms from liquid into a porous solid. Cold-mold molding is the mainstream process for modern high-resilience foam. It can react and mold near room temperature, consumes less energy, and enables more precise control of the cells.

Core control logic:

Temperature and mixing: Raw-material temperature must remain stable (typically 22–25°C), and the mold is kept at a constant temperature (about 45–50°C). Temperature fluctuations can seriously affect reaction speed and cell uniformity. The materials must be instantly mixed uniformly through high-speed mixing and injected into the mold within an extremely short time after mixing.

Cell-structure optimization: The performance soul of high-resilience foam lies in its high open-cell rate and uniform, fine cell structure. Ideally, cells are interconnected; when compressed, air can be expelled and re-enter quickly.

This is the physical basis for “instant rebound” and good breathability. Through precise control of silicone surfactants, this ideal structure can be created. Cells that are too large or uneven will disperse support and slow rebound.

Curing And Post-Treatment:

The “Stabilizer” Of Performance That Prevents Later Sagging

Foam just demolded only “looks” ready; internal chemical reactions have not fully ended, so curing is needed to “set” it.

Room-temperature curing: After demolding, the foam should be placed for 48–72 hours in a constant temperature and humidity environment to allow sufficient post-crosslinking of molecular chains and stabilize the cell structure. Foam with insufficient curing may meet initial performance targets, but is prone to permanent deformation after use.

Post-curing (thermal treatment): To further improve performance, the foam can be treated for several hours in an oven/tunnel at 60–80°C. This process can significantly improve mechanical strength, rebound, and fatigue resistance, keeping the foam in good condition after long-term use.

Crushing treatment (for specific needs): For applications with extremely high requirements, “crushing” is sometimes performed, meaning the foam is strongly compressed once.

This is intended to break any remaining extremely thin cell membranes, ensuring the open-cell structure is fully interconnected, thereby achieving the best breathability and rebound while further reducing long-term compression set.

Process Out-Of-Control Warnings:

These Problems Mean The Process Wasn’t Tuned Properly!

Slow rebound, soft sagging, weak support: Possibly due to insufficient polyol reactivity, a low isocyanate index, or inadequate curing.

Hard and brittle, with cracks: Usually caused by excessive crosslinker, an overly high isocyanate index, or uncontrolled post-curing temperature.

Uneven density, local dents: Problems often arise in the foaming stage: uneven mixing of materials, uneven mold temperature, or incorrect shot-weight calculation.

Shrinkage and deformation: An overly high closed-cell rate, insufficient curing, or a fundamental imbalance in the formulation.

16/05/2026

How to Identify High-Quality Flexible PU Foam?

When purchasing flexible PU foam, the most frustrating scenario for buyers is often: “The sample looks perfect, but the bulk order performs poorly.”

Even when density fully meets specifications, physical performance can still vary between batches. In a complex supply chain, relying solely on experience or hand feel is not enough. Buyers must establish an objective evaluation system based on production logic.

Below are the three core dimensions for identifying high-quality flexible PU foam:

I. Observing Internal Structure: Cell Morphology Determines the Foundation

The physical performance of foam is fundamentally determined by the microscopic structure of thousands of internal cells.

Cell uniformity:
After cutting, high-quality foam should show fine, evenly distributed cells. Visible large voids, bubbles, or hardened lumps indicate insufficient mechanical shear during foaming or unstable chemical reactions.

Cell openness and airflow:
Good flexible PU foam must have a high open-cell rate. Only when cells are interconnected can air be expelled instantly under compression. Excessive closed cells trap air inside, causing delayed rebound and even post-curing shrinkage or deformation.

Cell wall toughness:
Closely observe the cell “struts.” In high-quality foam, the cell walls are intact and elastic. This directly determines tear resistance and whether the foam will crumble or shed under repeated stretching.

II. Breaking Down Core Indicators: Using Data to Expose Quality Traps

Data is the only objective language. Focus on these four parameters that most strongly affect product lifespan:

Ball rebound resilience ≥45%:
This is a standard indicator of foam elasticity (typically for high-resilience grades). Foam meeting this value provides effective kinetic energy feedback. Low rebound leads to a soft, weak feel and faster elastic fatigue.

Compression set ≤30%:
This parameter directly defines service life. After being compressed for 22 hours at 70 °C, less permanent deformation indicates a more stable crosslinked network. This is the baseline for preventing irreversible sagging in sofas or mattresses.

Support feel (ILD):
High-quality foam delivers layered support—soft under light pressure and firm under deep compression. This tactile experience comes from precise indentation load control and defines overall comfort.

Tensile strength ≥0.8 MPa:
This is a rigid toughness indicator. Quality foam should resist tearing. Foam that can be easily torn by hand often indicates improper chain extender usage or insufficient curing time during production.

III. Tracing Process Origins: Ensuring Batch-to-Batch Stability

The core value of professional flexible PU foam supply lies in stability. Evaluate factory control capability through the following:

Density consistency verification:
Randomly sample different positions from bulk foam blocks and weigh them. High-level factories control foaming temperature variation within ±1 °C and maintain stable pressure, ensuring minimal density deviation from the first block to the hundredth. Large density fluctuations indicate insufficient equipment precision.

Odor and safety assessment:
Freshly unpacked foam with pungent or irritating odors often contains excessive free monomers (such as TDI). This reflects incomplete reaction conversion, affecting physical properties and posing long-term environmental and health risks.

Aging resistance:
Quality formulations include appropriate antioxidants to slow yellowing and powdering. While yellowing is inevitable, high-quality foam maintains physical performance stability longer across diverse climate conditions.

Veteran Technicians’ Practical Inspection Methods

When no instruments are available on-site, use these quick screening techniques:

Press and release forcefully:
Upon releasing your hand, the foam should rebound instantly like a spring. Delayed recovery signals poor quality.

Tear resistance test:
Pull firmly at the foam edge. Only foam with strong toughness and elongation qualifies.

Smell test:
No sharp chemical odor or off-smell is the minimum acceptance threshold.

Light transmission check:
Hold a thin foam piece against bright light. Uniform light pe*******on without dark clumps indicates extremely stable foaming.

11/05/2026

What Will Define the PU Foam and Mattress Supply Chain in 2026?

Introduction: From Industry Consolidation to the Era of Efficiency

Entering 2026, the global polyurethane industry has moved into a phase of deep structural reconfiguration. As milestone mergers and acquisitions—such as ADNOC’s integration with Covestro—enter the ex*****on stage, and Wanhua Chemical further consolidates its global capacity, the industry is shifting from pure scale expansion toward a new cycle driven by technological innovation and multi-dimensional compliance.

For global mattress manufacturers, the core challenge in 2026 lies in building a highly resilient supply system amid a volatile macroeconomic environment.

I. Supply Side: Post-Consolidation Dividends and Risk Hedging

The large-scale industry consolidation of 2025 begins to release operational synergies in 2026. Global raw material distribution systems are becoming more efficient, and supply volatility of high-performance isocyanates (MDI/TDI) has eased to some extent.

However, despite increasing supply-side concentration, raw material prices remain dynamic due to a higher share of green electricity, fluctuations in natural gas prices, and the internalization of carbon emission costs. Against a backdrop of geopolitical uncertainty and volatile global shipping costs, partners with globally distributed chemical production bases and strong supply-chain resilience now offer value that goes far beyond simple low-price strategies.

II. Green Barriers: From Voluntary Sustainability to Mandatory Market Access

By 2026, sustainability has shifted from a brand value enhancer to a hard entry threshold for international markets. Regulatory frameworks in Europe and North America covering carbon footprint accounting and recycled material ratios are now fully implemented.

CO₂-based polyols and bio-based raw materials produced via the mass balance approach have made significant progress within mainstream mattress supply chains. Beyond CertiPUR-US and GRS certifications, ISCC PLUS certification has emerged as a core indicator for evaluating suppliers’ expertise in circular economy and bio-based material applications.

III. Manufacturing: Breakthroughs in High-Efficiency Processes and Thermal Management

Advancements in production technology are redefining the functional boundaries of foam, enabling finished products to achieve stronger differentiation in downstream markets. Optimization of new-generation amine catalysts and the adoption of low-energy foaming systems have effectively reduced volatile organic compound emissions and overall energy intensity during production.

Meanwhile, the introduction of graphene and high-performance aerogel additives is significantly enhancing mattress thermal management capabilities and long-term antibacterial performance. Through deep integration with flexible PU foam substrates, mattress components are evolving from single-function support materials into multifunctional performance modules.

IV. Risk Management: Compliance and Digital Traceability Systems

As trade compliance requirements grow increasingly complex in 2026, supply-chain transparency has become a matter of survival. National energy-efficiency and emission standards for polyurethane products are accelerating the phase-out of outdated capacity.

The adoption of safer railway transport modes and the establishment of digital traceability systems not only reduce hazardous chemical logistics risks but also provide complete carbon footprint tracking for end products, meeting the regulatory expectations of global buyers.

Conclusion: A Return to the Fundamentals of Business Strategy

The polyurethane market in 2026 stands at a critical transition point—from scale-driven growth to quality-driven development. As green standards become mandatory thresholds and supply-chain stability replaces price volatility as the core competitive variable, the underlying logic of industry competition has fundamentally changed.

In this cycle, companies that maintain strategic focus, invest deeply in sustainable technologies, and embrace digital transparency will secure a decisive global competitive advantage over the next five years.

05/05/2026

Why Does Cell Structure Define the Performance and Quality of PU Cleaning Sponges?

Using the same polyurethane (PU) material, why can some sponges remove grease effectively while others only smear dirt around?

The core reason lies in how the foaming process controls the cell structure.

1. Cross-Application Comparison: Not All Pores Are Meant to “Fight”

The performance of a sponge is determined by its microstructure. Sponges designed for different applications have fundamentally different pore architectures:

Professional PU cleaning sponges:
Designed with a high open-cell structure, typically featuring an open-cell rate of 75%–85%. This highly interconnected network is the foundation for water absorption and effective physical friction.

Furniture cushioning sponges (sofas / mattresses):
Optimized for support and resilience. To maintain elasticity, their structure contains a large proportion of cell membranes (semi-closed cells). As a result, water cannot flow through effectively and friction is insufficient, making them unsuitable for cleaning.

Filter sponges:
Although fully open-cell and extremely permeable, their struts are very thin and lack mechanical strength. Under repeated friction, they are prone to breaking and shedding.

Cosmetic sponges:
Designed for extreme fineness, with pore sizes as small as 10–50 μm. Their ultra-soft texture is suitable only for gentle application and cannot remove hardened grease or industrial contaminants.

2. Mechanism Breakdown: How Do Cells Enable Physical Cleaning?

The high efficiency of PU cleaning spongess comes from precise internal structural cooperation:

Capillary absorption system:
Interconnected cells generate capillary action that locks water within the pores. This forms a liquid lubrication film that protects the surface being cleaned and helps release detergents evenly.

Physical stripping effect:
Under microscopic observation, each open-cell edge acts as a mechanical friction point. These strong strut frameworks function like miniature scrapers, physically detaching contaminants and trapping them deep within the pores to prevent recontamination.

High-density compression processes:
Some high-performance sponges undergo high-temperature compression to further densify the cell structure. This process creates microfibrillar struts that pe*****te fine gaps and enable deep cleaning.

3. Production Parameters: Matching Specific Cleaning Scenarios

Manufacturers must precisely control pore size (μm) and density (kg/m³) to meet different market demands:

Delicate surfaces (50–100 μm):
Suitable for tableware and glass. Fine cells ensure evenly distributed friction and leave no water marks after wiping.

Heavy-duty contamination (100–200 μm or larger):
Ideal for kitchens or car washing. Larger pores can accommodate more grease and coarse particles, and allow easier rinsing and debris removal.

Industrial-grade cleaning (high density):
Density typically ranges from 20–50 kg/m³. Stronger strut toughness ensures durability on rough industrial equipment surfaces without shedding or tearing.

4. Quality Control Guide: How to Evaluate Foaming Quality?

As professional producers, we can quickly assess quality through three physical dimensions:

Cell uniformity:
For precision PU cleaning spongess, pore size should be highly consistent. Non-uniformity indicates issues with the foaming machine’s pressure stability or raw material ratios.

Mechanical rebound feel:
Compress the sponge firmly and observe its response. A high-quality product should provide clear mechanical feedback. Loose texture or weak rebound indicates insufficient strut strength.

Load stability when wet:
Observe the sponge after full water absorption. A high-quality sponge should maintain its geometric shape even in a wet state, without collapsing or softening excessively.

In essence, producing a good sponge means constantly competing with these microscopic cells. When parameters are controlled within the right window, product performance speaks for itself. Hopefully, these micro-level insights can offer fresh inspiration to those working on the foaming front line.

23/04/2026

How to Correctly Evaluate the Performance Indicators of Flexible PU Foam?

This guide outlines the key technical indicators and validation methods used to determine the quality of flexible polyurethane foam. These evaluation criteria are critical for material selection in furniture, automotive interiors, and mattress industries.

Core International Performance Verification Framework

The performance verification of flexible foam materials is typically based on the following three major international standard systems:

ASTM D3574: A comprehensive set of test methods for slab, bonded, and molded polyurethane cellular materials.
ISO 2439: Measurement specification for hardness (load-bearing capacity) of flexible cellular polymeric materials.
EN ISO 1856: Test standard for permanent deformation (compression set) of flexible cellular materials.

I. Material Intrinsic Characteristics and Initial Properties

This section evaluates the basic physical structure and mechanical stability of the foam.

1. Apparent Density

This parameter defines the weight of material contained per unit volume of foam and serves as a fundamental indicator for cost control and durability estimation. Apparent density is typically expressed in pounds per cubic foot or kg/m³. Verification follows ASTM D3574 (Test A) and ISO 845.

2. Tensile Strength and Ultimate Elongation

Tensile strength records the peak stress required to pull a specimen of defined cross-sectional area until fracture, expressed in psi. Ultimate elongation records the percentage extension of the specimen prior to break. These tests are specified in ASTM D3574 (Test E) and EN ISO 1798.

3. Tear Resistance

This indicator quantifies the energy required to propagate an initiated tear and is particularly critical for applications involving stitching or stapling. Results are expressed in pounds-force per linear inch. Verification follows ASTM D3574 (Test F) and EN ISO 8067.

4. Air Permeability

This test evaluates the ease with which air passes through the foam structure. Low permeability may indicate slow recovery after compression and insufficient breathability. Measurement is conducted in accordance with ASTM D3574 (Test G).

II. Support Performance and User Experience

This category of tests is directly related to product comfort, support strength, and elastic feedback.

1. Stiffness and Load-Bearing Evaluation

Indentation Force Deflection (IFD)
This is the primary method for determining foam stiffness or firmness. A large foam specimen is indented, and the force required to reach a specified percentage of deflection (such as 25% or 65%) is recorded. Verification follows ASTM D3574 (Test B1/B2) and ISO 2439.

Compression Force Deflection (CFD)
This indicator quantifies the overall stiffness of smaller test specimens, expressed in psi. The key difference is that CFD applies uniform pressure across the entire cross-section, whereas IFD simulates localized loading. Verification follows ASTM D3574 (Test C).

Critical Performance Ratios

Sag Factor: The ratio of 65% R IFD to 25% R IFD; higher values indicate superior support under heavy loads.
Guide Factor: The ratio of 25% IFD to foam density, used to evaluate cost-effectiveness.
Recovery Ratio: The ratio of 25% R IFD after unloading to its initial value.

2. Dynamic Response Characteristics

Resilience / Ball Rebound
This test measures material elasticity by expressing the rebound height of a steel ball as a percentage of its initial drop height. Verification follows ASTM D3574 (Test H) and ISO 8307.
Recovery Time
This test is specific to viscoelastic (slow-recovery) foams and measures the time required for a specimen to return to a predetermined thickness after removal of compressive stress. Verification follows ASTM D3574 (Test M).
Hysteresis Loss
This indicator quantifies the energy absorbed and dissipated during compression and release cycles. Lower loss values indicate faster recovery of support characteristics. Verification follows ASTM D3574 (Test N).

III. Long-Term Use and Environmental Resistance

These tests are designed to predict product lifespan and assess resistance to repeated wear and environmental stress.

1. Compression Set

This test determines the residual permanent thickness loss after the foam has been subjected to controlled temperature and sustained compression. Results are expressed as a percentage of the original thickness; lower values indicate better durability. Verification follows ASTM D3574 (Test D) and EN ISO 1856.

2. Dynamic Fatigue Assessment

This test predicts real-world service life by simulating repeated stress and quantifying the percentage decay in load-bearing capacity. Subtests include static constant stress, roller shear dynamic stress, and constant-force repeated impact. Verification follows ASTM D3574 (Test I) and EN ISO 3385.

3. Accelerated Aging Procedures

These tests evaluate performance degradation by exposing foam to extreme environments. Types include high-temperature steam aging (Test J), high-temperature dry aging (Test K, e.g., 140 °C air), and humid heat aging (Test L, e.g., 50 °C at high humidity). Verification follows ASTM D3574 (Tests J, K, L).

18/04/2026

Why Does Foam Burning or Soft Collapse Occur? Revealing the “Triple-Balance Technique” in Low-Density Polyurethane Foaming

I. Analysis: Chemical Origin of Core Burning and Soft Collapse

Producing low-density flexible PU foam is a challenge against the thermal-stability limit of the material. The essence of core burning or red-core formation is that the internal temperature surpasses the safety threshold of 160 °C, causing thermal degradation of polymer chains.

The key framework for controlling core burning lies in precisely managing three core variables: gas volume, internal heat value, and reaction rate.

Heat source (exothermic paradox):
The TDI–water reaction is the main exothermic contributor. Its heat value and reaction rate determine the absolute internal heat of the foam.

Heat-dilution principle:
The larger the gas volume (CO₂ from water and vaporized physical blowing agent), the stronger the heat-dilution effect. When heat value stays constant, larger gas volume results in lower internal temperature.

Core contradiction:
Increasing water increases gas volume, but the rise in heat value is much larger than the increase in gas volume. Therefore, increasing water alone easily causes temperature runaway.

II. Balance Technique 1: Precise Control of Heat and Volume

To solve high-temperature issues, the “less water + more physical blowing agent” strategy must be used to reduce internal heat value while maintaining low density.

1. Core Tool: Formula Calculation Using “Effective Water (W)”

Because physical blowing agents (such as MC) provide cooling but also slow the gel reaction due to solvent effects—leading to soft collapse and lower hardness—the formula must not be based solely on total water.

Core formula:
Effective water (W) = actual water (W1) − virtual water (W2)
Virtual water (W2) = MC dosage ÷ 8.4

Safety window:
Only when effective water W is kept within the 2.5–4.5 “golden window” can low density, no core burning, and hardness consistency be achieved.
Below 2.5 → density fails
Above 4.5 → core burning is inevitable

2. Selection and synergy of physical blowing agents

In extreme low-density conditions (10–15 kg/m³), MC alone cannot provide sufficient cooling. Selection must consider cooling efficiency, environmental impact, and cost:

MC/Pentane: Moderate cost, good cooling, but flammability and hardness loss risks

HFOs: Ultra-low GWP, eco-friendly replacement for HFCs, suitable for ultra-low density but expensive

Supercritical CO₂: Zero ODP & GWP, highly efficient, works with water to reduce urea formation and maintain softness, but requires high-pressure equipment

III. Balance Technique 2: Matching Chemical Reaction Rates

Reaction rate is the third critical variable. Faster reactions release heat more intensely, increasing peak temperatures.

1. Catalyst adjustment and reaction-rate control

Catalyst dosage is the most direct way to control reaction rate:

Reducing amine catalysts (slow-down):
A33 and other amines mainly catalyze the TDI–water exothermic reaction. When slight core burning occurs, the most common first adjustment is reducing amine to slow heat-release speed.

Gel-reaction matching:
T9 (tin catalysts) primarily control the gel reaction (skeleton formation). Foaming rate and gel rate must match:
Gel too slow → collapse or soft collapse
Gel too fast → insufficient expansion time for gas

2. Raw-material reactivity & TDI index corrections

Polyol reactivity:
High-reactivity polyols (e.g., EO-containing polyols) increase reaction speed and require reducing T9 to prevent excessive reaction and poor cell structure.

TDI index:
Adjusting the index affects water reaction and residual-TDI reaction.
Higher index suppresses water reaction (slower) but increases residual-TDI reaction.
Its effect on temperature must be calculated precisely—not judged by experience.

IV. Balance Technique 3: Counterbalancing Additives and External Conditions

1. “Heating” vs “Cooling” additives

Cooling additives:
Inorganic fillers like calcium carbonate do not react but slow reaction speed via physical hindrance, resulting in cooling.

Heating additives:
Most flame retardants are acidic and catalyze the TDI–water reaction, accelerating exothermic reactions and increasing internal temperature.
After adding flame retardants, the correction must combine:
less water + more MC + lower A33.

2. Dynamic corrections in process conditions

Temperature of raw materials:
Higher material temperature (e.g., 25 °C → 35 °C) accelerates all reactions and requires reducing water and physical blowing agents.

Mixing speed:
Too high → entrained air + blowing-agent gas → collapse
Too low → poor mixing → reduce total blowing-agent dosage

Mold pressure (in molded foam):
Compressed conditions suppress gas expansion, requiring increased blowing-agent levels to ensure full mold filling.

V. Conclusion: Criteria for Optimal Foaming

Producing low-density flexible PU foam requires mastering a triple balance of thermodynamics, kinetics, and formula precision.

The core adjustment principle is synchronizing gas-generation rate with polymer-network curing rate.

Optimal results must show: uniform cell structure, target density, no burning/collapse defects, and mechanical properties (resilience, hardness) meeting design standards.

Kabond Foam

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