Plastic additives, also known as plastic additives, are some compounds that must be added to polymers (synthetic resins) when they are molded to improve their processing performance or to improve the properties of the resin itself.
Different additives are selected according to different purposes
Toughening – Choose elastomers, thermoplastic elastomers and rigid toughened materials.
Reinforcement – Choose from glass fibers, carbon fibers, whiskers and organic fibers.
Flame retardant - bromine (common bromine and environmental bromine), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardant, antimony trioxide, hydrated metal hydroxide.
Antistatic - all kinds of antistatic agents.
Electrically conductive – carbons (carbon black, graphite, carbon fibers, carbon nanotubes), metal fibers and metal powders, metal oxides.
Magnetic - ferrite magnetic powders and rare earth magnetic powders include samarium cobalt (SmCo5 or Sm2Co17), NdFeB (NdFeB), samarium iron nitrogen (SmFeN), and alnico magnetic powders.
Thermal conductivity – metal fibers and powders, metal oxides, nitrides and carbides, carbon materials such as carbon black, carbon fibers, graphite and carbon nanotubes, semiconductor materials such as silicon and boron.
Heat-resistant – glass fibers, inorganic fillers, heat-resistant agents such as substituted maleimides and β crystalline nucleating agents.
Transparent – nucleating agent, for PP α the sorbitol series of crystalline nucleating agents Millad 3988 works best.
Wear-resistant - graphite, molybdenum disulfide, copper powder, etc.
Insulation – calcined kaolin.
Barrier – mica, montmorillonite, quartz, etc.
Surface treatment of additives
The good compatibility between the additives and the resin can ensure that the additives and resins are dispersed according to the expected structure, ensure the completion of the design indicators, and ensure that the effect is long-lasting during the service life, and is resistant to extraction, migration and precipitation. For example, most formulations require uniform dispersion of additives and resins, while barrier formulations require additives to be distributed in layers in the resin.
With the exception of a few additives such as surfactants, good compatibility with resins is the key to exerting their efficacy and increasing the amount of additives. Therefore, it is necessary to find ways to improve or improve its compatibility, such as surface activation with compatibilizers or coupling agents.
The surface of all inorganic additives is treated to improve the modification effect. In particular, fillers are the most obvious, and others include glass fibers, inorganic flame retardants, etc.
There are also coupling agents and compatibilizers, coupling agents such as silanes, titanates and aluminates, and the compatibilizer is the maleic anhydride grafted polymer corresponding to the resin.
Dosage of additives
Some additives have an optimal dosage
For example, conductive additives can be formed into the electrical path, and then added to have no effect; Another example is the coupling agent, the surface coating can be done, and then it is useless; Another example is an antistatic agent, which can form a leakage charge layer on the surface of the product.
The relationship of the additive to other components
Symphony
Refers to the effect of two or more additives added together in a plastic formulation that is higher than the average value of their individual additives.
In the anti-aging formulation, the specific synergistic effect is the combination of two phenolic antioxidants with different hydroxyl ortho-substituent hindrances.
In flame retardant formulations, the main synergistic examples are: in the halogen/antimony composite flame retardant system, the halogenated flame retardant can react with Sb2O3 to form SbX3, and SbX3 can isolate oxygen, so as to achieve the purpose of increasing the flame retardant effect.
Antagonistic effect
Refers to the fact that two or more additives in a plastic formulation are less effective than the average when they are added alone.
In the formulation of anti-aging plastics, the specific antagonistic effects are: HALS light stabilizers are not used in combination with thioether co-antioxidants, because the acidic components of thioethers inhibit the light stabilizing effect of HALS.
In the formulation of flame retardant plastics, the main examples of antagonistic effects are: halogenated flame retardants and silicone flame retardants are used together, which will reduce the flame retardant effect; Red phosphorus flame retardants are used in combination with silicone flame retardants, which also have an antagonistic effect.
The components of the formula should be mixed evenly
Some components are to be added in batches
For formulations where the amount of filler is too large, it is best to add the filler in two parts. The first time is in the hopper and the second time is in the middle side of the opening. If PE is added to 150 parts of aluminum hydroxide for halogen-free flame retardant formula, it must be added in two parts, otherwise it cannot be granulated.
For the coupling agent treatment of the filler, it is generally necessary to spray it in three times to disperse evenly, and the coupling effect is good.
Reasonable arrangement of feeding sequence
In the formulation of PVC or filler masterbatch, the feeding sequence of each material is very important. In the filling masterbatch formulation, the filler should be added first, and the water in it can be removed after mixing and heating, which is conducive to subsequent coupling treatment. In PVC formulations, external lubricants should be added later, so as not to affect the uniform mixing of other materials.
Negative effects of the formulation on other properties
The designed formula should not deteriorate or minimally affect the basic physical and mechanical properties of the resin, at least retain the original properties, and preferably improve some properties of the original resin by the way.
But the objective fact is that there are two sides to everything, and when one performance is improved, the other performance may be reduced. Therefore, when designing the formulation, it is important to consider it holistically so as not to affect other properties as much as possible. For example, the high filling formula has a great impact on the mechanical properties and processing properties of composite materials, the impact strength and tensile strength are greatly reduced, and the processing fluidity becomes poor.
If the product has specific requirements for the mechanical properties of the composite material, specific compensation should be made in the formula, such as adding elastomer materials to make up for the impact performance, and adding lubricants to improve the processing performance.
What are some of the properties in the formulation that are often affected?
Impact
Most inorganic materials and some organic materials reduce the impact properties of the formulation.
To compensate for impact strength, elastomers need to be added to the formulation. Such as PP/talc/POE formula in filling system, ABS/decabromo/antimony trioxide/toughener formulation in flame retardant system.
transparency
Most inorganic materials have an impact on transparency, and choosing an inorganic material with a refractive index similar to that of resin will have less effect on transparency.
Recently, transparent filler masterbatch is more popular, mainly for HDPE plastic bags, adding special varieties of talcum powder has little impact on transparency, but it is not absolutely no effect.
Organic materials also have an impact on transparency, such as PVC toughening, only MBS does not affect transparency, while CPE, EVA, ACR all affect transparency.
In inorganic flame retardant materials, colloidal antimony pentoxide does not affect transparency.
Colorability
In the formula design, we must pay attention to the color and discoloration of the additives themselves, some additives themselves are very dark, which will affect the color of the products, and it is difficult to process light-colored products. If the carbon black is black, only dark-colored products can be processed.
Others, such as graphite, red phosphorus, molybdenum disulfide, metal powder and industrial slag, all have their own colors, so they should be paid attention to when selecting. There are also some additives that are white in themselves, but change color due to high temperature reaction during processing, such as wollastonite itself is white, but it becomes light gray after being filled into resin and processed.
Other features
The thermal conductivity modification of plastics is generally the addition of metal and carbon thermal conductive agents, but such thermal conductive agents are conductive agents, which will improve the electrical conductivity while improving the thermal conductivity, thereby affecting the insulation.
Thermal conductivity is used in many materials that require insulation, such as circuit boards, connectors, packaging materials, etc. For this reason, thermal conductivity can not be added to insulate and conduct heat, but only insulating thermal conductives, such as ceramic metal oxides.
What other properties should the formulation have
The formula should ensure appropriate machinability to ensure the molding of the product, and have no adverse impact on the processing equipment and the use environment.
The heat resistance of the additives in the composite materials should be good, and no evaporation and decomposition will occur at the processing temperature (except for cross-linking agents, initiators and foaming agents); the addition of additives should have little impact on the original processing performance of the resin; the wear and corrosion of the equipment should be as small as possible, and no toxic gases should be released during processing, so as not to damage the health of employees.
liquidity
Most of the inorganic fillers affect the processability, such as the large amount added, the corresponding addition of processing modifiers to compensate for the loss of fluidity, such as the addition of lubricants, etc.
Organic additives generally promote processability, such as decabromodiphenyl ether and tetrabromobisphenol A flame retardants can promote processing fluidity, especially the effect of tetrabromobisphenol A is more obvious.
Generally, the right amount of lubricant needs to be added to the modified formulation.
heat tolerance
Ensure that the additives do not decompose during processing, except for the foaming agent, initiator, and cross-linking agent that must be decomposed due to functional requirements.
Precautions
Due to its low decomposition temperature, aluminum hydroxide is not suitable for use in PP and can only be used in PE.
Tetrabromobisphenol A is not suitable for the flame retardant of ABS due to its low decomposition temperature.
Most organic dyes have a low decomposition temperature and are not suitable for high-temperature processing of engineering plastics.
The decomposition temperature of spices is low, generally below 150°C, and resins with low processing temperatures such as EVA can only be used as carriers.
Due to the strong shear effect during processing, antioxidants need to be added to the modified plastic formula to prevent thermal decomposition from occurring, resulting in yellowing of the raw material.
Environmental friendliness of plastic formulation components
Requirements: All kinds of additives in the formula are harmless to the operator, harmless to the equipment, harmless to the user, and harmless to the contact environment.
In the past, the scope of environmental protection requirements was small, but it was only non-toxic to food, drugs and other contact with the human body.
Now the requirements are higher, and indirect contact with the human body is not possible, and there must be no pollution to the environment, such as soil, water, atmosphere, etc.
Prices and sources of additives
On the basis of meeting the above requirements of the formula, the lower the price of the formula, the better. In the specific selection of additives, the same kind of additives must be selected with low price.
Choose low-cost raw materials whenever possible – reducing product costs
Whenever possible, stock ingredients – no need to buy them
Locally sourced raw materials are selected wherever possible – low transportation costs reduce inventory and save working capital
Choose domestic raw materials as much as possible - imported raw materials are greatly affected by factors such as foreign exchange, trade policies, and transportation time
Choose generic raw materials as much as possible - new raw materials are not available in a small number of distribution units, and their performance is unstable
Article source: Eighth Element Plastic Edition
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