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The key points of the selection of plastic additives are the most comprehensive interpretations I have ever seen.

2022-05-18 Page view : 39 views

Choice of resin

(1) Selection of varieties of plastic particles
The plastic particles should be selected with the performance closest to the modification purpose. The advantage of this is that the amount of additives can be saved, so as to reduce the production cost and reduce the process flow.
The most common example: If you want to get wear-resistant modified varieties, plastic particles (resins) should first consider choosing the three major wear-resistant resins PA, POM, UHMWPE; for transparent modification, the resin should first consider choosing the three major transparent resins PS, PMMA, PC.

(2) Selection of resin fluidity
The viscosity of various plasticized materials in the formula should be close to ensure processing fluidity. For materials with widely different viscosities, a transition material should be added to reduce the viscosity gradient.
(3) Plastics are divided into high fluidity plastics, low fluidity plastics and illiquid plastics.

Details as follows:
High fluidity plastics – PS, HIPS, abs, PE, PP, PA, etc.
Low-flow plastics – PC, MPPO, PPS, etc.

Immobile plastics – PTFE, UHMWPE, PPO, etc.

Different processing methods require different fluidity, so the grades are divided into injection molding grade, extrusion grade, blow molding grade, calendering grade, etc.
Different modification purposes require different fluidity, such as high filling requiring good fluidity.

(4) The selectivity of resin to additives
Such as PPS cannot add lead and copper additives, PC cannot use antimony trioxide, these can lead to depolymerization. At the same time, the acidity and alkalinity of the auxiliary agent should be consistent with the acidity and alkalinity of the resin; otherwise there will be a reaction between the two.

Selection of Auxiliaries

(1) Select additives according to the purpose to be achieved

The specific selection range of additives is as follows:
Toughening – choose elastomers, thermoplastic elastomers and rigid toughening materials.

Reinforcement – Choose from glass fibers, carbon fibers, whiskers and organic fibers.
Flame retardant – bromine (common bromine and environmentally friendly bromine), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardant, antimony trioxide, hydrated metal hydroxide.

Antistatic – all kinds of antistatic agents.
Conductive – carbon (carbon black, graphite, carbon fiber, carbon nanotube), metal fiber and metal powder, metal oxide.
Magnetism – Ferrite magnetic powder and rare earth magnetic powder include samarium cobalt (SmCo5 or Sm2Co17), neodymium iron boron (NdFeB), samarium iron nitrogen (SmFeN), and AlNiCo magnetic powder.
Thermal conductivity – metal fibers and metal 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 resistance – glass fibers, inorganic fillers, heat-resistant agents such as substituted maleimides and β-crystal nucleating agents.
Transparent – nucleating agent, for PP, the sorbitol series Millad 3988 of α crystal nucleating agent has the best effect.
Wear resistance – graphite, molybdenum disulfide, copper powder, etc.
Insulation – Calcined Kaolin.
Barrier – mica, montmorillonite, quartz, etc.

(2) The additives are selective to the resin

Red phosphorus flame retardant is effective for PA, PBT, PET; nitrogen flame retardant is effective for oxygen-containing types, such as PA, PBT, PET, etc.; nucleating agent has good effect on copolymerized polypropylene; glass fiber heat-resistant modification is effective for crystallization It has good effect on crystalline plastics, but poor effect on amorphous plastics; carbon black filled conductive plastics has good effect in crystalline resins.

(3) Surface treatment of additives

The compatibility between the additive and the resin should be good, so as to ensure that the additive and the resin are dispersed according to the expected structure, to ensure the completion of the design indicators, to ensure that the effect is lasting within the service life, and it is resistant to extraction, migration and precipitation. For example, most formulations require the additives to be uniformly dispersed in the resin, and for barrier formulations, the additives are expected to be distributed in layers in the resin. In addition to a few additives such as surfactants, good compatibility with resin is the key to exerting its efficacy and increasing the addition amount. Therefore, we must try to improve or improve its compatibility, such as using a compatibilizer or a coupling agent for surface activation treatment.
After the surface of all inorganic additives is treated, the modification effect will be improved. In particular, fillers are the most obvious, and others include glass fibers and inorganic flame retardants.
The surface treatment is mainly based on coupling agents and compatibilizers, such as silanes, titanates and aluminates, and the compatibilizers are maleic anhydride grafted polymers corresponding to resins.

Reasonable dosage of additives

(1) The more additives are added, the better
Specifically, such as flame retardant, toughening agent, magnetic powder, barrier, etc., the more the amount added the better.
(2) Some additives have the best value
For example, conductive additives can be formed after the electrical path is formed, and then adding them has no effect; another example is a coupling agent, which can be coated on the surface, and it is useless; another example, an antistatic agent can be formed on the surface of the product to form a charge discharge layer.

The relationship between additives and other components

1. Synergy
Synergy means that the effect of two or more additives in a plastic formulation is higher than the average of their individual additions.

(1) In the anti-aging formula, the specific synergistic effects are:
Two kinds of phenolic antioxidants with different steric hindrance of hydroxyl ortho-substituents have synergistic effect when used together;
Typical BASF antioxidants 1010 and 168 play the role of primary and secondary antibodies, respectively.
(2) In flame retardant formulations, there are many examples of synergy, mainly including:
In the halogen/antimony composite flame retardant system, the halogen flame retardant can react with Sb2O3 to generate SbX3, and SbX3 can isolate oxygen to achieve the purpose of increasing the flame retardant effect.

2. Confrontation

The antagonistic effect means that the effect of two or more additives added together in the plastic formulation is lower than the average value of their individual additions.
(1) In the formulation of anti-aging plastics, there are many examples of antagonism, mainly including:
HALS light stabilizers are not used in combination with thioether auxiliary antioxidants, because the acidic components of thioethers inhibit the light stabilization of HALS.

(2) There are also examples of antagonism in the formulation of flame retardant plastics, mainly including:
The combination of halogen-based flame retardants and silicone flame retardants will reduce the flame retardant effect; the combination of red phosphorus flame retardants and silicone flame retardants also has an antagonistic effect. 
The ingredients of the formula should be mixed evenly

(1) Some components should be added in batches
For formulations with too much filler added, it is best to add the filler in two portions. The first time is in the feeding hopper, and the second time is the feeding port on the middle side. If PE adds 150 parts of aluminum hydroxide halogen-free flame retardant formula, it should be added in two times, otherwise it cannot be granulated.
For the coupling agent treatment of the filler, it is generally necessary to spray it in three times to achieve uniform dispersion and good coupling effect.

(2) Reasonably arrange the feeding sequence
In the formulation of PVC or filler masterbatch, the order of addition of various materials is very important. In the formulation of the filler masterbatch, the filler should be added first, and the water in it can be removed after mixing and heating, which is beneficial to the subsequent coupling treatment. In the PVC formulation, the external lubricant should be added later, so as not to affect the uniform mixing of other materials.

Negative effects of formulation on other properties

The designed formula should not degrade or affect the basic physical and mechanical properties of the resin in a minimal way, at least retain the original properties, and preferably improve some properties of the original resin by the way. But the objective fact is that everything has two sides. When one performance is improved, other performances may be reduced. Therefore, when designing the formula, it must be considered comprehensively, and other properties should not be affected as much as possible. For example, the high filling formula has a great influence on the mechanical properties and processing properties of the composite material, the impact strength and tensile strength are greatly reduced, and the processing fluidity is deteriorated. 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 an elastomer material to compensate for the impact performance, and adding a lubricant to improve the processing performance.  

Here are a few of the properties that are often affected.

(1) Impact

Most inorganic materials and some organic materials reduce the impact properties of the formulation. To compensate for impact strength, an elastomer needs to be added when designing the formulation. Such as the PP/talc/POE formulation in the filling system, and the ABS/decabromo/antimony trioxide/toughening agent formulation in the flame retardant system. 

(2) Transparency

Most inorganic materials have an impact on transparency. Selecting an inorganic material with a refractive index similar to that of the resin will have less impact on transparency. Recently, transparent filler masterbatch is more popular, mainly for HDPE plastic bags, adding special varieties of talc has little effect on transparency, but 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, and ACR all affect its transparency.
In inorganic flame retardant materials, colloidal antimony pentoxide does not affect the transparency.

(3) Color

When designing the formula, we must pay attention to the color and discoloration of the additives themselves. Some additives are very dark in color, which will affect the color of the product, and it is difficult to process light-colored products. If carbon black is black, only dark products can be processed; others such as graphite, red phosphorus, molybdenum disulfide, metal powder and industrial slag have their own colors, so pay attention when selecting them. There are also some additives that are white, but discolored due to high temperature reaction during processing. For example, wollastonite itself is white, but it becomes light gray after being filled into resin.

(4) Other properties

The thermal conductivity modification of plastics is generally by adding metal and carbon thermal conductivity agents, but these thermal conductivity agents are also conductive agents, which can improve the electrical conductivity while improving the thermal conductivity, thereby affecting the insulation. And heat conduction is used in many materials that require insulation, such as circuit boards, connectors, packaging materials, etc. For this reason, in order to insulate and conduct heat, it is not possible to add conductive heat-conducting agents, but only insulating heat-conducting agents, such as ceramic metal oxides.

The formulation should be machinable

The formula should ensure proper machinability, so as to ensure the molding of the product, and have no adverse effect on the processing equipment and the use environment. The heat resistance of the additives in the composite material is better, and there is no evaporation and decomposition at the processing temperature (except for crosslinking agents, initiators and foaming agents); the addition of additives has little effect on the original processing properties of the resin; the added The wear and corrosion of the auxiliary agent to the equipment should be as small as possible, and no toxic gas will be released during processing, which will damage the health of the processing personnel.

(1) Liquidity

Most inorganic fillers affect the processability. If the amount added is large, it is necessary to add processing modifiers to compensate for the lost fluidity, such as adding lubricants.
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.
The general modified formula needs to add an appropriate amount of lubricant.

(2) Heat resistance

Ensure that the additives do not decompose during processing, except that the foaming agent, initiator, and crosslinking agent must be decomposed due to functional requirements. Also note the following:
Aluminum hydroxide is not suitable for use in PP due to its low decomposition temperature, but can only be used in PE.
Tetrabromobisphenol A is not suitable for flame retardancy of ABS due to its low decomposition temperature.

Most organic dyes have a low decomposition temperature and are not suitable for engineering plastics processed at high temperatures.
The decomposition temperature of spices is low, generally below 150 ℃, and only resins with low processing temperature such as EVA can be used as carriers.
Modified plastic formulations need to be added with antioxidants due to the strong shearing effect during processing to prevent thermal decomposition and cause the raw materials to turn yellow.

Environmental friendliness of plastic formulation components

The specific requirements are that 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, and it was only necessary to be non-toxic to food, medicine, etc. in contact with the human body. Now the requirements are higher, and the indirect contact with the human body is not enough. It must not pollute the environment, such as soil, water, and atmosphere.

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