(1) Selection of types of plastic particles
Plastic particles should be selected with properties closest to purpose of modification. Advantage of this is that it can save amount of additives added, thereby reducing production costs and process flow.
The most common example: If you want to obtain wear-resistant modified varieties, plastic particles (resins) must first consider choosing three major wear-resistant resins PA, POM, and UHMWPE; for transparent modification, resin must first consider choosing three major transparent resins. PS, PMMA, PC.
(2) Selection of resin fluidity
Viscosity of various plasticizing materials in formula should be close to ensure processing fluidity. For materials with widely different viscosities, transition materials should be added to reduce viscosity gradient.
(3) Plastics are divided into high-flow plastics, low-flow plastics and non-flow plastics
Details as follows:
High flow plastics - PS, HIPS, abs, PE, PP, PA, etc.
Low flow plastics - PC, MPPO, PPS, etc.
Non-flowing plastics - PTFE, UHMWPE, PPO, etc.
Different processing methods require different fluidity, so grades are divided into injection molding grade, extrusion grade, blow molding grade, calendering grade, etc.
Different modification purposes require different fluidity. For example, high filling requires good fluidity.
(4) Selectivity of resin to additives
For example, lead- and copper-containing additives cannot be added to PPS, and antimony trioxide cannot be used in PC, as these can lead to depolymerization. At the same time, acidity and alkalinity of additive should be consistent with acidity and alkalinity of resin, otherwise the two will react.

 

(1) Select additives according to purpose to be achieved
Specific selection range of additives is as follows:
Toughening - Choose elastomers, thermoplastic elastomers and rigid toughened materials.
Reinforcement – Choose from glass fiber, carbon fiber, whiskers and organic fibers.
Flame retardant - bromine (ordinary bromine and environmentally friendly bromine), phosphorus, nitrogen, nitrogen/phosphorus composite intumescent flame retardant, antimony trioxide, hydrated metal hydroxide.
Antistatic - various types 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 three categories: 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 fiber, graphite and carbon nanotubes; semiconductor materials such as silicon and boron.
Heat resistance - glass fiber, inorganic fillers, heat-resistant agents such as substituted maleimides and beta crystal nucleating agents.
Transparent - nucleating agent. For PP, sorbitol series Millad 3988, an alpha crystalline nucleating agent, has the best effect.
Wear resistance - graphite, molybdenum disulfide, copper powder, etc.
Insulation – Calcined kaolin.
Barrier - mica, montmorillonite, quartz, etc.
(2) Additive is selective for resin
Red phosphorus flame retardants are effective for PA, PBT, and PET; nitrogen-based flame retardants are effective for oxygen-containing species, such as PA, PBT, PET, etc.; nucleating agents are effective for copolymerized polypropylene; glass fiber heat-resistant modification is effective for crystallization It has good effect on conductive plastics but poor effect on amorphous plastics; carbon black filled conductive plastics has good effect on crystalline resins.
(3) Surface treatment of additives
Compatibility between additive and resin must be good, so as to ensure that additive and resin are dispersed according to expected structure, to ensure completion of design indicators, effect is long-lasting during service life, is resistant to extraction, migration and precipitation. For example, most formulas require additives and resin to be evenly dispersed, while for barrier formulas, additives are expected to be distributed in layers in resin. Except for a few additives such as surfactants, good compatibility with resin is the key to exerting its effect and increasing amount of addition. Therefore, efforts must be made to increase or improve its compatibility, such as using compatibilizers or coupling agents for surface activation.
After surface of all inorganic additives is treated, modification effect will be improved. Especially fillers are the most obvious, and others include glass fiber, inorganic flame retardants, etc.
Surface treatment mainly uses coupling agents and compatibilizers. Coupling agents include silanes, titanates and aluminates. Compatibilizer is maleic anhydride graft polymer corresponding to resin.

(1) The more additives you add, the better.
Specifically, such as flame retardants, toughening agents, magnetic powder, barriers, etc., the more added, the better.
(2) Some additives have optimal adding amounts.
For example, conductive additives can be added after forming an electrical path, then adding them will have no effect; for example, coupling agents can be surface-coated, but adding them is useless; and for example, antistatic agents can form a charge-discharging layer on the surface of product.

1. Synergy
Synergy means that effect of two or more additives in a plastic formula when added together is higher than average value when added alone.
(1) In anti-aging formula, specific synergistic effects are:
Combined use of two phenolic antioxidants with different steric hindrance of ortho-substituents on the hydroxyl group has a synergistic effect;
Typical BASF antioxidants 1010 and 168 play the role of primary antioxidant and auxiliary antioxidant respectively.
(2) In flame retardant formulas, there are many examples of synergy, mainly including:
In halogen/antimony composite flame retardant system, halogen flame retardant can react with Sb2O3 to form SbX3. SbX3 can isolate oxygen to achieve purpose of increasing flame retardant effect.
2. Antagonism
Antagonistic effect means that effect of two or more additives in a plastic formula when added together is lower than average value of adding them alone.
(1) In anti-aging plastic formulas, there are many examples of antagonistic effects, mainly including:
HALS light stabilizers should not be used together with thioether auxiliary antioxidants because acidic components generated by thioethers inhibit light stabilizing effect of HALS.
(2) In flame-retardant plastic formulas, there are also examples of antagonistic effects, mainly including:
Combined use of halogen flame retardants and silicone flame retardants will reduce flame retardant effect; combined use of red phosphorus flame retardants and silicone flame retardants also has antagonistic effects.

(1) Some components need to be added in batches
For formulas where amount of filler added is too large, it is best to add filler in two batches. The first time is in feeding hopper, and the second time is in the middle side feeding port. If PE is added to a halogen-free flame retardant formula of 150 parts of aluminum hydroxide, it must be added in two times, otherwise granulation will not be possible.
For coupling agent treatment of fillers, it is generally sprayed in three times to achieve even dispersion and good coupling effect.
(2) Reasonably arrange order of feeding
In formula of PVC or filled masterbatch, order of adding various materials is very important. In filling masterbatch formula, filler must be added first. After mixing and heating, water in it can be removed, which is beneficial to subsequent coupling processing. In PVC formula, external lubricant must be added later to avoid affecting uniform mixing of other materials.

Designed formula should not degrade or minimally affect basic physical and mechanical properties of resin. At the very least, original properties should be retained, and it is best to improve some properties of original resin. But objective fact is that everything has two sides. When improving one performance, it may reduce other performance, which can be said to be a loss of the other. Therefore, when designing formula, all aspects must be considered to avoid affecting other properties as much as possible. For example, high-filling formulas have a great impact on mechanical properties and processing properties of composite materials. Impact strength and tensile strength are greatly reduced, and processing fluidity becomes worse. If product has specific requirements for mechanical properties of composite materials, specific compensation must be made in formula, such as adding elastomer materials to compensate for impact performance and adding lubricants to improve processing performance.

 

Here are a few frequently affected performances.
(1) Impact
Most inorganic materials and some organic materials reduce impact properties of formulation. In order to compensate for impact strength, elastomers need to be added when designing formulation. Such as PP/talc/POE formula in filling system, and ABS/decabromide/antimony trioxide/toughener formula in flame retardant system.
(2) Transparency
Most inorganic materials have an impact on transparency. Choosing an inorganic material with a refractive index similar to that of resin will have less impact on transparency. Recently, transparent filling masterbatch has become more popular, mainly for HDPE plastic bags. Adding special varieties of talcum powder has little impact on transparency, but it does not have absolutely no impact.
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.
Among inorganic flame retardant materials, colloidal antimony pentoxide does not affect transparency.
(3) Color
When designing formula, you must pay attention to color and discoloration of additives themselves. Some additives themselves are very dark in color, which will affect color of product and make it difficult to process light-colored products. If carbon black is black, it can only process dark-colored products; others such as graphite, red phosphorus, molybdenum disulfide, metal powder and industrial slag are themselves colored, so pay attention when selecting them. There are also some additives that are white themselves, but change color due to high-temperature reactions during processing. For example, wollastonite itself is white, but after being filled into resin and processed, it turns light gray.
(4) Other properties
Thermal conductivity modification of plastics generally involves adding metal and carbon thermal conductive agents, but such thermal conductive agents are also electrically conductive agents. When improving thermal conductivity, they will also increase electrical conductivity, thereby affecting insulation. Thermal conductivity is often used in materials that require insulation, such as circuit boards, connectors, packaging materials, etc. For this reason, if you want to insulate and conduct heat, you cannot add conductive thermal conductive agents. You can only add insulating thermal conductive agents, such as ceramic metal oxides.

Formula must ensure appropriate processability to ensure molding of product, have no adverse effects on processing equipment and use environment. Additives in composite materials should have good heat resistance and will not evaporate or decompose at processing temperature (except for cross-linking agents, initiators and foaming agents); addition of additives should have little impact on original processing properties of resin; wear and corrosion of equipment should be as small as possible, toxic gases should not be released during processing and harm health of processing personnel.
(1) Liquidity
Most inorganic fillers affect processability. If amount is large, processing modifiers need to be added to compensate for loss of fluidity, such as adding lubricants.
Organic additives generally promote processability, such as decabromodiphenyl ether and tetrabromobisphenol A flame retardants, which can promote processing fluidity, especially tetrabromobisphenol A, which has a more obvious effect.
General modified formulas require addition of an appropriate amount of lubricant.
(2) Heat resistance
Ensure that additives do not decompose during processing, except for foaming agent, initiator, and cross-linking agent that must be decomposed due to functional requirements. Also note following points:
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 ABS flame retardancy due to its low decomposition temperature.
Most organic dyes have low decomposition temperatures and are not suitable for high-temperature processing of engineering plastics.
Decomposition temperature of spices is low, generally below 150℃, so only resins with low processing temperatures such as EVA can be used as carriers.
Modified plastic formulas require addition of antioxidants due to strong shear during processing to prevent thermal decomposition, which would cause raw materials to turn yellow.

Specific requirements are that all kinds of additives in formula are harmless to operator, equipment, user, and environment. In the past, scope of environmental protection requirements was small, and it only required that food, medicine, etc. be non-toxic when they come into contact with human body. Nowadays, requirements are higher, and those that come into direct contact with human body are not allowed. They must be non-polluting to environment, such as soil, water, atmosphere, etc.

 

On the basis of meeting above requirements of formula, the lower price of formula, the better. When specifically selecting additives, be sure to choose low-price types for similar additives.
Choose low-priced raw materials as much as possible - reduce product costs
Choose ingredients that are in stock when possible—no need to buy them.
Choose local raw materials as much as possible - low transportation costs, which can 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 general-purpose raw materials as much as possible—new raw materials have fewer distribution units, are difficult to purchase, and have unstable performance.