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Three flame retardant acrylate lotion adhesives, aluminum hydroxide (ATH), melamine phosphate (MP) and MP/pentaerythritol (PER), were prepared by mechanical blending. The results showed that the tensile strength of the system decreased with the increase of flame retardant addition, while the oxygen index (LOI) increased with the increase of flame retardant addition; At the same level, the ATH modified adhesive system has a higher residue rate; The results of the cone calorimeter indicate that the addition of various flame retardants can effectively reduce the heat release rate (HRR), mass loss rate (MLR), and smoke release rate (SPR) of the adhesive system; Scanning electron microscopy (SEM) shows that the expansion flame retardant effect of the modified adhesive system is optimal when the mass ratio of MP to PER is 3:1

1 Experimental section

1.1 Raw materials

· Matrix: acrylate lotion (commercial lotion adhesive)

Flame retardant: ATH aluminum hydroxide; MP melamine phosphate; PER Pentaerythritol

· Preparation method: mechanical and physical blending, adding flame retardant powder into acrylate lotion, stirring and dispersing to obtain flame retardant adhesive, without chemical copolymerization.

1.2 Test items

Oxygen index LOI, tensile strength, TG thermogravimetric analysis, cone calorimetry CONE, SEM scanning electron microscopy observation of carbon layer morphology.

Excerpts from the results of two core experiments

2.1 Effect of Flame Retardant Addition on Oxygen Index and Tensile Strength

Common laws:

1) An increase in the amount of flame retardant added leads to an increase in the oxygen index (LOI) and improved flame retardancy;

2) The filling of flame retardant powder increases, the cohesion of the adhesive is destroyed, and the tensile strength continues to decrease; Contradiction point: Improving flame retardant performance will sacrifice the mechanical bonding performance of the adhesive.

① ATH aluminum hydroxide system (inorganic filler type)

Flame retardant mechanism: endothermic decomposition dehydration, forming a metal oxide residue barrier layer;

Characteristics: The highest thermogravimetric residue rate is achieved with the same amount of addition; Belonging to solid phase barrier flame retardant, without expansion foaming;

Shortcoming: A high addition amount is required to achieve a high LOI, significantly reducing the adhesive bonding strength.

② MP melamine phosphate (single component of phosphorus and nitrogen)

Phosphorus nitrogen flame retardant, with both acid and gas sources; No external carbon source, the expanded carbon layer is thin and the integrity is average.

③ MP PER expansion complex system (MP as acid source gas source, PER as carbon source)

Optimal ratio: MP: PER=3:1 (mass) SEM observation: This ratio can generate a continuous, porous expanded carbon layer when heated, which is dense and complete, and has the best expansion flame retardant effect; When the ratio deviates from 3:1, the carbon layer cracks, there are too many holes, and the insulation protection decreases.

2.2 Cone Calorimetry Results (Combustion Behavior)

All three flame retardants have achieved:

Reduce the peak heat release rate (HRR);

Reduce the quality loss rate MLR and slow down the decomposition of the matrix;

Reduce the smoke release rate SPR to achieve smoke suppression effect.

Comparison of Differences:

ATH system has outstanding smoke suppression effect, high residual carbon, but no expansion;

The MP/PER expansion system relies on a foam carbon layer for insulation, resulting in a significant decrease in heat release but a lower residue rate than ATH.

2.3 Thermogravimetric TG Results

1. Pure acrylate lotion adhesive: almost completely decomposed at high temperature, with very low carbon residue;

2. ATH modification: Thermal decomposition is divided into two steps, ATH dehydration absorbs heat, and a large amount of inorganic alumina residue remains at high temperatures;

3. MP PER system: When heated, esterification and dehydration occur to form carbon, forming a carbon layer in the medium temperature range, and the high-temperature carbon layer gradually oxidizes and ablates.

3 Main conclusions of the article

1. Flame retardant acrylate lotion adhesive can be prepared by mechanical blending; The amount of flame retardant added is a double-edged sword: while improving the LOI flame retardant performance, it significantly reduces the tensile bonding strength of the adhesive.

ATH inorganic system: high residue rate, good smoke suppression effect, but does not expand, requiring high filling amount.

3. MP/PER expansion system, MP: PER=3:1 is the optimal ratio, forming a good expansion carbon layer, and the expansion flame retardant effect is better than adding MP alone.

4. All three flame retardant systems can reduce heat release, quality loss, and smoke release.

5. Limitations: This article is a physical blend system, and the flame retardant is an external filler, which poses risks of migration and precipitation; A large amount of powder filling will damage the storage stability of lotion and adhesive bonding performance.

4 inspirations

1. Expansive MP PER system is used for acrylic lotion adhesive, and the ratio of 3:1 is the key reference;

2. Relying solely on the addition of blended flame retardants results in a trade-off between flame retardancy and adhesive properties; To achieve both, it is necessary to consider the copolymerization modification of reactive phosphorus containing monomers;

3. Inorganic ATH is suitable for smoke suppression scenarios, but high filling can seriously degrade adhesion.