Expandable graphite-magnesium hydroxide-straw fiber-polyurethane rigid foam composite insulation material: innovative preparation and performance research

With the increasing demand for efficient thermal insulation materials in the construction and industrial fields, rigid polyurethane foam (RPUF) has been widely used due to its excellent thermal insulation performance. However, the improvement of its flame retardant and mechanical properties remains a challenge. This study aims to develop a new composite thermal insulation material by introducing expandable graphite, magnesium hydroxide and straw fiber to improve the flame retardancy, mechanical properties and environmental friendliness of polyurethane rigid foam.

Overview of preparation method

Straw fiber pretreatment:

Select suitable straw fiber (such as corn straw) as filler.

The straw fiber is crushed and the particle size is controlled at 1-5mm.

Immerse it in a 12% sodium hydroxide solution to improve its surface properties and enhance its bonding with the polyurethane matrix.

Wash and dry the treated straw fiber.

Addition of expandable graphite and magnesium hydroxide:

Mix expandable graphite (EG) and magnesium hydroxide (MH) evenly, and use their synergistic effect to improve the flame retardant properties of the composite material.

It is possible to use electrochemical intercalation and other technologies to prepare magnesium hydroxide/expandable graphite composites.

Preparation of polyurethane rigid foam:

Add pretreated straw fiber, expandable graphite and magnesium hydroxide to polyurethane prepolymer in proportion.

After mixing evenly, inject into the mold and form rigid polyurethane foam through the foaming process.

After foaming, solidify and cool to obtain the final product.

Performance study

Physical properties:

Investigate indicators such as density, compression strength, tensile strength, etc.

Thermal properties:

Evaluate thermal conductivity, limiting oxygen index (LOI), thermal stability, etc.

Flame retardant properties:

Test burning rate, smoke density, combustion residue rate, etc.

Environmental performance:

Detect the amount of toxic gas released, biodegradability, etc.

Research significance

Improve flame retardancy:

The addition of expandable graphite and magnesium hydroxide significantly improves the flame retardant properties of polyurethane rigid foam and reduces the risk of fire.

Enhance mechanical properties:

As a filling material, straw fiber not only enhances the mechanical properties of polyurethane rigid foam, but also reduces costs.

Environmentally friendly:

Renewable resources (such as straw fiber) are used to replace some non-renewable materials to reduce the impact on the environment.

This composite insulation material has a broad application prospect due to its excellent performance and environmental friendliness, especially in the fields of building insulation and industrial insulation.