What are the elements of plastic modification formula design?

What are the elements of plastic modification formula design?

Plastic modification is a method to change the properties and improve the quality of plastics by adding additives and fillers. At the same time, plastic modification is also the most effective way to reduce the cost of plastics. The factors of formula design in plastic modification mainly include: material selection, compounding, dosage and mixing mode. Each element interacts with each other to either complement or cancel each other out, so designing a high-performance, easy-to-process, low-cost formula is not a easy task.

Resin Selection

1. Resin Varieties and Grades

The selected target resin and the target performance need modification has the closest performance: first of all, in the resin variety screening, such as: improve the toughness of the resin, the selection of ABS, SBS and other resins; Transparent modification, the resin should first consider the selection of three transparent resin PS, PMMA, PC.

After the target resin is identified, the resin brand is selected. Specific grades of resin with more specific performance indicators, will make the target selection more deterministic. Resin selection: select big brands, general resin, to ensure that the later purchase of resin is more convenient.

2. The Complexity of Resin

The compound of the selected target resin and the main resin, that is, the selected target resin and the main resin have compatibility, can form a whole, there is no phase separation. The target resin can achieve the modified performance objectives.

3. Viscosity of Resin and Fluidity of Composite Resin

In the formulation, the viscosity of the selected target resin should be close to that of the main resin. If the viscosity of the selected target resin is too large, it will lead to high viscosity of the composite resin, and modifiers need to be added to reduce the viscosity gradient. For example: toughening modification of PA66, adding PA6 as modifier in flame retardant formula; PA6 toughened and flame retardant formula was readded to HDPE as a modifier.

The change of viscosity will affect the change of its fluidity, and ultimately affect the change of processing methods, such as: injection grade, extrusion grade, blow molding grade, calendering grade and so on. The main factors affecting the fluidity of the same resin are the molecular weight and the arrangement of molecular chains, such as linear molecules and shape molecules. Among them, high fluidity resins include: PS HIPS, ABS, PE, PP, PA, etc.; Low fluidity resin: PC, MPPO, etc.; Non-flowing resin: PTFE, UHMWPE/PPO.

Selection of Additives

1.Purposeful selection of additives

Different types of auxiliaries have different target performance, the auxiliaries added to the system can fully its expected function, and achieve the target specified indicators. Among them, the prescribed indicators are generally national standards, international standards, or customer performance requirements. The properties of common target resins modified are as follows.

1) Flame retardancy: inorganic phosphorus, organic halide, organophosphoride, organic silicon and nitride etc.

2) Reinforcement: fiber and whisker two categories. Glass fiber, asbestos fiber, carbon fiber, whisker, quartz fiber, graphite fiber and ceramic fiber; PAN fiber, POLYETHYLENE fiber, PA fiber, PC fiber, PVC fiber and polyester fiber; Boron fiber and aluminum, titanium, calcium and other metal whiskers.

3) Toughening: high impact resistance resin, such as CPE, MBS, ACR, SBS, ABS, EVA, modified petroleum resin (MPR), etc. High impact resistant rubber, such as ethylene propylene rubber (EPR), ethylene propylene diene rubber (EPDM), nitrile rubber (NBR), styrene butadiene rubber, natural rubber, butyl rubber, chloroprene rubber, polyisobutene and butadiene rubber, etc.

4) Wear resistance: graphite, MoS2, silica, etc.

5) Degradability: starch filling, degradation additives, etc.

2. The influence of the form of auxiliaries on the composite properties

The same additives, its morphology distribution is also different, relative to the effect of modification is not the same. For powder additives, the key factor is its particle size.

1) The smaller the particle size is, the more beneficial it is to the tensile strength and impact strength of the filling material. For example, in terms of impact strength, the impact strength will increase twice when the particle size of antimony trioxide is reduced by 1μm;

2) The smaller the particle size of flame retardants, the better the flame retardant effect, such as ABS adding 4% antimony trioxide particle size of 45μm and adding 1% antimony trioxide particle size of 0.03μm flame retardant effect is the same;

3) The smaller the particle size of the colorant, the higher the coloring power, the stronger the covering power, the more uniform color. But the particle size of colorant is not the smaller the better, there is a limit value, and the limit value of different performance is different;

4) Taking carbon black as an example, the smaller its particle size is, the more likely it is to form a network conductive pathway to achieve the same conductive effect, and the amount of carbon black added is reduced. But like colorants, there is a limit to particle size, particle size is too small to gather and difficult to disperse, but the effect is not good.

For fiber additives, the higher the fiber degree of additives, the better the enhancement effect. Among them, the degree of fibrosis of auxiliaries can be expressed by L/D. The molten state is better than the powder to maintain the length-diameter ratio, reduce the probability of broken fiber, so it is also a better way to add.

3.Compatibility of additives and resins

Good compatibility between resin and additives is an important basis to ensure good performance of additives, to ensure good durability, extraction resistance, migration resistance and precipitation resistance during use. Good compatibility is a basic requirement, even barrier formulations also require additives in the resin middle layer distribution. The main methods to improve resin compatibility:

1) Compatibility additives, such as surfactants, should be added in quantities to maximize their effectiveness.

2) Surface treatment. Compatibilizer or coupling agent is used as surface treatment agent to improve the compatibility of resin and auxiliary agent. Common coupling agents include silane, titanate and aluminate. The compatibilizer includes a maleic anhydride graft polymer corresponding to the resin. The additives that need surface treatment include inorganic additives and fiber additives.

4. The amount of additives added

The appropriate amount of additives is not only to improve the target resin to the appropriate properties, but also based on the economic basis of low cost. For different additives to add different requirements:

1) flame retardant, toughening agent, magnetic powder, barrier agent, performance Angle, although the more the amount of the better, but also to check and ratify the cost;

2) conductive auxiliaries, generally forming circuit paths;

3) antistatic agent, the surface can form a charge leakage layer;

4) Coupling agent, surface coating can be formed.

5. The relationship between resin and auxiliaries

The addition of additives can not lead to the deterioration of the resin itself, such as: PPS can not join lead and copper additives, PC can not use antimony trioxide, which can lead to depolymerization; At the same time, the acid and alkali of the additives should be consistent with the acid and alkali of the resin, otherwise there will be a reaction between the two.

6. Relationship between additives and other components

In a formula, in order to take into account multiple purposes at the same time, a variety of different additives need to be added. The interaction of additives is very complex, the main overview:

1) Independent of each other without influence;

2) Synergistic effect: multiple auxiliaries with heavy formula promote each other, so that the overall effect is higher than the average of single auxiliaries;

3) Mutual elimination: when two or more additives are added together, the effect is lower than the average value of their addition alone. For example, in the formulation of anti-aging plastics, sulfur ether co-antioxidants and HALS light stabilizers are not used at the same time, because the acidic components bred by sulfur ether inhibit the light stability of HALS.

Uniform mixing

Uniform mixing is the basic requirement of plastic formula modification, and also requires the uniform distribution of additives in the formation of resin. The uneven distribution of additives can not only improve the performance of the original resin, but also may be worse than the performance of pure resin because of the uneven distribution of filler. For example: the use of filler on the mechanical properties and processing properties of the material, the dispersion is not uniform, not only the mechanical properties are greatly reduced, the processing properties will be affected. The common ways to improve the uniform mixing of additives are as follows:

1) Reasonable ordering of the fillers added, such as: in the coupling treatment process, the fillers are advanced, after heating and dehydration, and then the coupling agent is added;

2) Components should be added into the system in primary and secondary order. Large quantities of fillers can be added into multiple batches to facilitate uniform mixing. Coupling agent treatment, generally should be divided into three spray can disperse evenly, the coupling effect is good.

Selection of Formula

Formula workability that modified plastic formula has workability, is to meet the molding plastic modified after both products molding care. The main embodiment of the formula processability: auxiliaries good heat resistance, no evaporation loss, decomposition inactivation; The formula formed on the equipment wear and corrosion is small, no toxic gas release, can be used as the standard of assessment.

1. Fluidity of modified plastics

The fluidity of plastics is the main aspect that affects the processing performance of plastics, and it is also the important basis to choose the plastic processing method. Generally speaking, the addition of inorganic filler will lead to the decrease of flow performance, and it is necessary to add flow modifier for optimization.

2. Heat resistance

Heat resistance in accordance with two aspects:

1) Reduce the processing temperature of resin, processing temperature does not exceed the decomposition temperature of additives, to ensure the stable existence of additives, reflect the modification performance;

2) Add a certain amount of antioxidant additives, prevent the occurrence of thermal decomposition, affect the performance of the resin. Generally speaking, most organic dyes decomposition temperature is low, not suitable for high temperature processing of engineering plastics; The decomposition temperature of spices is low, generally below 150℃, and resin with low processing temperature such as EVA can only be used as the carrier.

3.Environmental protection of the formula

The environmental protection of the formula includes: harmless to the human body, equipment, environment and users. Human hygiene - resins and selected additives should be absolutely non-toxic or contained within specified limits. Environmental contamination - The selected component must not contaminate the environment.

4.Cost price and source

The lower of the price of plastic modification formula, the better, the use of additives in the implementation process according to the following principles:

1) Preferentially use low-price raw materials;
2) Preferentially use existing raw materials: no need to purchase, stable source, clear performance;
3) Preferential use of domestic raw materials: price fluctuations are less affected by foreign exchange and trade policies;
4) Give priority to nearby raw materials: reduce the cost of inventory;
5) General raw materials should be preferred: the source is wide and the performance is stable.