Discover how these key components determine the mechanical, thermal, and structural properties of versatile materials used in automotive, construction, and consumer products.
The comfortable resilience you feel in vehicle seats, the protective cushioning in appliance packaging, the thermal insulation in building materials - all these products utilize semi-rigid polyurethane foam.
Balancing between the softness of flexible foams and the rigidity of hard foams, this material has become essential in automotive interiors, furniture, and construction materials. Particularly, chain extenders and inorganic fillers are crucial elements that determine the magical properties of this material, where subtle adjustments can significantly alter the foam's strength, elasticity, and heat resistance2 .
Seats, headrests, armrests with optimal support and comfort
Insulation materials with excellent thermal properties
Protective cushioning for appliances and fragile items
Semi-rigid polyurethane foam exhibits intermediate characteristics between flexible and rigid foams2 . While flexible foams feature high elasticity and flexibility, and rigid foams are characterized by strong strength and stiffness, semi-rigid foams provide appropriate elasticity and resilience while maintaining a certain level of support strength2 .
High elasticity and flexibility
Used in mattresses, cushions
Strong strength and stiffness
Used in insulation panels
To understand and measure the physical properties of semi-rigid polyurethane, standard test methods such as ISO 844 (compression properties), ISO 1926 (tensile properties), and ISO 1209 (bending test) are used2 . These tests allow quantitative evaluation of the foam's mechanical characteristics.
Chain extenders serve to connect polyol and isocyanate chains during polyurethane synthesis, increasing the molecular weight of the polymer4 . This contributes to improving the mechanical strength and heat resistance of polyurethane.
Research shows that when polycaprolactone triol (PCL) is used as a chain extender, the foam exhibits uniform cell structure and high thermal and mechanical properties4 .
Particularly, the NCO/OH ratio (NCO index) is an important factor directly connected to the effectiveness of chain extenders. Research has shown that the NCO index around 0.98 exhibits optimal physical properties and uniform cell structure4 . This is because if the NCO index is too low, the degree of polymerization is insufficient, and if too high, it affects crosslink density.
Inorganic fillers disperse within the polyurethane matrix and reinforce the overall physical properties of the foam. Fillers improve mechanical strength, stiffness, heat resistance, and chemical resistance, and in some cases, also contribute to making the cell structure of the foam more uniform.
Additionally, certain inorganic fillers can help reduce the flammability of the foam.
A domestic research team conducted systematic experiments to elucidate the effects of chain extenders and inorganic fillers on the properties of semi-rigid polyurethane foam5 . This experiment represents a typical research case that provided important guidelines for performance optimization of semi-rigid polyurethane foam.
Polyol, isocyanate, chain extenders, fillers
Precise ratio adjustments
Controlled temperature and conditions
ISO standard mechanical tests
The experimental results showed that the type and amount of chain extenders significantly affected the tensile strength and heat resistance of the foam. When specific chain extenders were used and the NCO index was adjusted to around 0.98, uniform cell structure and high thermal and mechanical properties were observed4 .
In the case of inorganic fillers, using appropriate types and amounts could significantly improve the compressive strength and flexural strength of the foam. However, when the filler amount was too high, problems such as uneven cell structure of the foam, increased density, and decreased elasticity and elongation were also observed.
| Chain Extender Type | Tensile Strength | Elongation |
|---|---|---|
| PCL Series | Greatly Improved | Excellent |
| BG Series | Improved | Moderate |
| No Chain Extender | Baseline | Baseline |
| Filler Content (wt%) | Compressive Strength | Density |
|---|---|---|
| 0% | Baseline | Baseline |
| 5% | +15% | +3% |
| 10% | +25% | +7% |
| 15% | +30% | +12% |
| NCO Index | Tensile Strength | Foam Structure |
|---|---|---|
| 0.96 | Moderate | Relatively Uniform |
| 0.98 | High | Uniform |
| 0.99 | High | Somewhat Non-uniform |
Key reagents and their functions used by scientists researching and developing semi-rigid polyurethane foam.
Forms the basic skeleton of polyurethane. Polyether polyol and polyester polyol are used, and polycaprolactone triol (PCL) may be utilized as a chain extender4 .
Substances that extend polyurethane chains to increase molecular weight and strength. 1,4-butanediol among others is used4 .
Solid particles that reinforce the mechanical strength and heat resistance of foam.
Controls the reaction rate between polyol and isocyanate. Amine catalysts and tin catalysts among others are used1 .
Substances that create pores in foam. Water can be used as an environmentally friendly blowing agent6 , and when water reacts with isocyanate, it generates carbon dioxide to induce foaming.
Semi-rigid polyurethane foam has established itself as an indispensable material in modern industry due to its unique physical properties. And scientific research has proven that chain extenders and inorganic fillers play a key role in optimizing the performance of this material.
By systematically controlling the type and ratio of chain extenders, and the addition amount and type of inorganic fillers, the strength, elasticity, heat resistance, etc. of the foam can be precisely designed according to purpose.
Such research and development leads to various products that improve our quality of life, such as more comfortable and safe automotive interiors, high energy efficiency insulation materials, and packaging materials with excellent durability and cushioning. Scientists continue to explore the infinite combinations of chain extenders and inorganic fillers to develop semi-rigid polyurethane foams that are more environmentally friendly6 , have superior performance, and possess new functions.
Sustainable formulations
Optimized properties
Enhanced capabilities