Engineering Plastics Flame Retardant System Inventory

Engineering Plastics Flame Retardant System Inventory

With the continuous progress of polymer synthesis and processing technology, engineering plastics have penetrated into all areas of people's lives, in some areas that are often exposed to high temperature environments, the flame retardancy of engineering plastics has become an important indicator of its comprehensive performance.

I. Experimental Methods for Flame Retardancy of Plastics

The flame retardancy of plastics can be evaluated by the combustion test method, which is categorized into horizontal and vertical methods. The vertical method evaluates the flame retardancy of a material by measuring the duration of afterflame and afterglow, the range of burning, and the drop of particles. According to the behavior of the specimen, the material is classified into V-0, V-1, and V-2 levels (V means vertical burning) according to the criteria shown in Table 1.

Note: t₁, t₂ refer to the duration of afterflame; t₃ refers to the duration of afterglow; t_f refers to the total afterflame time.

Different plastics have different combustion properties. For example, PC itself has a certain degree of flame retardancy and can reach a V-2 level in the vertical combustion test. However, ABS is flammable and cannot be graded. Flame retardant modification of plastics through the addition of flame retardants can delay combustion and reduce the intensity of combustion. In the combustion process, plastics not only burn themselves but also produce droplets that can ignite other combustible materials, leading to the spread of fire with serious consequences. Therefore, flame retardant plastics often require the addition of anti-drip agents to prevent melt dripping during combustion.

II. Flame Retardant System for Engineering Plastics

• Flame Retardant

The flame retardants used in engineering plastics are mainly halogenated flame retardants and phosphorus flame retardants.

1. Halogenated flame retardants

Halogenated flame retardants are divided into chlorine flame retardants and bromine flame retardants.

Chlorine flame retardant is cheap, but it has poor thermal stability and is only suitable for products with processing temperature below 200℃.

Brominated flame retardants have high flame retardant efficiency, which is twice as much as that of chlorinated flame retardants, so the relative dosage is small, and because of its good mutual compatibility with the base resin, it has less influence on the mechanical properties of the material, so it has an important position in the field of flame retardant.

However, halogenated flame retardants in the combustion process will produce smoke and corrosive gases, etc., to bring serious secondary disasters to human health and the environment, so low-halogen or halogen-free environmentally friendly flame retardants are of great concern.

2. Phosphorus flame retardants

Phosphorus flame retardants have formed a wide range of varieties, including inorganic phosphates, phosphate esters, phosphorus heterophenols, phosphorus nitrile and red phosphorus.

Phosphorus flame retardants in the combustion process of decomposition of the formation of high-boiling oxygen-containing acid can promote polymer dehydration and carbonization, and the formation of carbonized residue protective layer, so that the polymer and air isolation. At the same time, the dehydrated water absorbs a large amount of heat, which can also reduce the surface temperature of the polymer, thus achieving the effect of flame retardant. The advantages of phosphorus-based flame retardants are low toxicity and corrosiveness, good thermal stability and long-lasting effect.

The European Union has banned the use of halogenated flame retardants such as polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers (PBDEs) in the manufacture of electronic equipment. Bisphenol A-bisphosphate diphenyl ester (BDP), a phosphate ester-based phosphorus flame retardant, is compatible with engineering plastics such as PC/ABS and has the advantages of good environmental performance, high thermal stability, and low impact on material properties, so it is widely used in electronic and electrical equipment such as cell phones, laptops, and televisions.

• Basic Resin

1. PC / ABS

PC has the advantages of high impact strength, creep resistance, good dimensional stability, heat resistance, transparency and dielectric properties, but also exists in the processing of poor mobility, prone to stress cracking, notch sensitivity, poor abrasion resistance and other shortcomings, ABS has a better resistance to chemicals and molding and processing, however, its heat and weathering resistance is relatively poor.

The two blended modified PC / ABS alloys in the performance of complementary, not only heat resistance, impact strength and tensile strength is better than ABS, and its melt viscosity is lower than that of PC, processing performance is good, the product of the internal stress and impact strength of the thickness of the product sensitivity are greatly reduced. pc / abs alloy is widely used in the automotive industry, communications equipment, electrical and electronic appliances, lighting equipment, and so on.

In order to meet the fire safety requirements in some applications, PC/ABS alloy must have good flame retardancy. For example, in the new energy vehicle charging pile and part of the electrical and electronic flame retardant grade to reach V-0.

Used in PC / ABS blending system is currently a better effect of good thermal stability of bis-phosphate esters and phosphate ester zwitterion, etc., of which BDP on PC / ABS alloys show good flame retardant properties.

2. PC

PC has good heat resistance, excellent optical properties, good dimensional stability, high mechanical strength and impact strength and other characteristics, widely used in household appliances, electronic appliances, automotive parts, mechanical equipment and optical instrument parts.

The ultimate oxygen index (LOI) of PC can reach 21% to 24%, and the material itself can reach UL94V-2 level flame retardant, but still cannot meet the higher requirements for flame retardant performance in special fields, such as electrical and electronic and automotive fields require PC flame retardant grade to V-0.

Flame retardant PC, with potassium perfluoroalkyl sulfonate (PPFBS) as the representative of the sulfonate flame retardant is the best effect, adding a small amount of sulfonate flame retardant can significantly improve the flame retardant properties of PC, to achieve a flame retardant grade of 1.6 ~ 3.0mmV-0, and after modification of the physical and mechanical properties of PC and the general-purpose PC equivalent.

Industrialized PC products in the most used phosphorus flame retardant is mainly triphenyl phosphate (TPP), resorcinol bis (diphenyl phosphate) (RDP) and BDP, in the flame retardant additive amount of 10% (mass fraction), 1.6mm thickness of PC up to the V-0 level, which is volatile at high temperatures, TPP only play a role in the gas phase of the flame retardant; RDP and BDP can play a flame retardant effect in the gas phase and solid phase at the same time.

TPP at room temperature for the solid state, thermal stability is relatively poor, easy to volatilize in the PC processing temperature, RDP and BDP at room temperature for the liquid, thermal stability is better, BDP better than RDP hydrolysis resistance.

3. ABS Resin

ABS has high gloss, good toughness, good heat and low temperature resistance, excellent processing performance, has excellent comprehensive mechanical properties.ABS electrical properties do not appear with the temperature and humidity changes and great changes, is a good insulating material, widely used in household appliances, audio-visual equipment, office supplies and electrical and electronic fields.

ABS resin is combustible, LOI 18.3% to 18.8%, according to UL94 standard belongs to HB level.ABS burns fast when it catches fire, and emits a lot of poisonous gas and black smoke, which is unfavorable for practical application.

At present, the main halogen flame retardants and Sb2O3 compounding use, halogen antimony synergistic effect of ABS flame retardant modification. Flame retardant ABS is mainly used in telephones, computers, liquid crystal displays (LCD) and other electrical and electronic equipment shells, automotive components and external components, small kitchen appliances, tool boxes, vacuum cleaner shells and so on.

4. HIPS

HIPS is made of polystyrene (PS) and polybutadiene (PB) through the copolymerization of the two common advantages, easy to process, good dimensional stability and excellent electrical insulation, high impact resistance, is widely used in food packaging, household appliances, electronic products and military materials, such as shell packaging and other fields.

However, the LOI of HIPS is only 18%, easy to burn, in order to improve the safety of use, it must be flame retardant modification. Used for HIPS flame retardant modification of the main bromine flame retardants such as decabromodiphenyl ethane (DBDPE), most of the synergistic effect with Sb2O3, with excellent flame retardant effect.

5. PBT

PBT is a crystalline saturated polyester, with excellent mechanical properties, good dimensional stability, good electrical insulation and resistance to chemicals, etc., widely used in automobiles, electronic appliances, machinery and other fields.

However, PBT has poor flame retardant properties (UL94HB level), easy to burn in the air, difficult to become charcoal, easy to drip when burning, and releases a large amount of smoke and toxic gases, easy to produce a relatively large number of hazards, so it must be flame retardant modification.

Flame retardants for PBT flame retardant modification is mainly halogenated flame retardants, more commonly used brominated flame retardants such as DBDPE, brominated epoxy resins, etc., through the synergistic effect with the Sb2O3, to achieve excellent flame retardant effect.

Flame retardants used in PBT also include aluminum diethylphosphonate (ADP) or its magnesium hydroxide, aluminum hydroxide and other complex products.

6. PA

PA has good mechanical properties, electrical properties and more prominent lubricating properties, widely used in electronic components and automotive parts and other fields.

Unmodified PA flame retardant grade UL94V-2, LOI of 20% to 22%, in contact with an open flame, rapid combustion will occur, releasing a large amount of heat, but also due to the presence of molten flame drop phenomenon, which creates conditions for the further spread of the open flame.

In order to prevent fire hazards, the industry has clear flame retardant requirements for PA composites used in automobiles, electrical appliances and other products, which are generally required to reach UL94V-0 level.

Halogenated flame retardants are widely used in PA due to their good compatibility with PA and high flame retardant efficiency.Flame retardants used in PA also include aluminum diethylphosphonate (ADP) or its compounded products with magnesium hydroxide and aluminum hydroxide.

In summary, at present, in the flame retardant system of engineering plastics, flame retardant PC/ABS, flame retardant PC mainly use phosphorus flame retardant BDP. flame retardant ABS, flame retardant HIPS, flame retardant PBT, flame retardant PA mainly use bromine flame retardant.

• Antidropping Agent

Early anti-drip agents were products such as chlorinated polyethylene and silicone rubber, which were gradually replaced by high molecular weight polytetrafluoroethylene (PTFE) as the mainstream of the market due to issues of environmental friendliness, maneuverability and migration. At the same time PTFE has also been proved to form compounds with antimony under combustion state to promote gas phase flame retardancy.

PTFE has the property of fibrillation under the action of shear force, and in the process of plastic processing, it forms a network structure running through the matrix of the plastic. In the case of heat, PTFE itself does not burn, and has the property of contraction, therefore, its interpenetrating fibrillated network structure can prevent the plastic from dripping, thus increasing the flame retardant properties of the plastic.

Specially modified coated PTFE, added to flame retardant material formulations, plays a flame retardant and anti-drip role, helping plastics to achieve higher flame retardancy standards.

Compared with conventional PTFE pure powder, coated PTFE has excellent dispersibility and ease of operation, no agglomeration at room temperature, no wrinkles in injection-molded products, no crystalline dots in black and white products, and the improvement of product surface gloss is especially obvious. Due to good compatibility, the impact strength is less affected in high impact formulations.

Anti-drip agent is suitable for PC, ABS, PC/ABS, HIPS, PBT, PA flame retardant plastics which need to reach V-0 or V-1 flame retardant grade.

In the field of engineering plastics flame retardancy, YINSU Flame Retardant has been dedicated to the development of advanced flame retardant solutions, offering a wide range of flame retardants tailored for different types of plastics. With a strong focus on research and development, the company has achieved significant breakthroughs in creating environmentally friendly and efficient flame retardants that meet the growing demands of various industries. YINSU Flame Retardant continues to push the boundaries of technology, developed special flame retardants for different engineering plastics, such as PET-55D and YS-F22B, not only enhance the safety of engineering plastics but also contribute to a more sustainable future.