Elements in The Design of Plastic Modification Formulas

Plastic modification is a method of improving the quality of plastics by adding additives, fillers, etc. to alter their properties. Meanwhile, plastic modification is also the most effective way to reduce the cost of plastics. The elements of formula design in plastic modification mainly include material selection, compounding, dosage, and mixing method. The interaction between various elements can be either mutual assistance or mutual cancellation. Therefore, designing a high-performance, easy to process, and low-cost formula is not an easy task.

01 Selection of resin

1. Types and grades of resins

The selected target resin has the closest performance to the target resin that needs to be modified: first, screen the resin varieties, such as improving the toughness of the resin and selecting resins such as ABS and SBS; Transparent modification requires the first consideration of selecting the three major transparent resins PS, PMMA, and PC.

After determining the target resin, select the grade of the resin. The specific grade of resin has more specific performance indicators, which will make the target selection more deterministic. Choose resin: Choose large brands and universal resins to ensure more convenient resin procurement in the later stage.

2. Composite properties of resin

The composite properties of the selected target resin and the main resin, that is, the selected target resin and the main resin have compatibility and can form a whole without phase separation. The target resin can achieve the performance goal of modification.

3. The viscosity of resin and the flowability of composite resin

In the formula, the viscosity of the selected target resin should be close to that of the main resin. The selected target resin has a high viscosity, which can lead to a high viscosity of the composite resin. It is necessary to add a modifier to reduce the viscosity gradient. For example, PA66 toughening modification, adding PA6 as a modifier in the flame retardant formula; PA6 toughening modification, adding HDPE as a modifier to the flame retardant formula.

The change in viscosity will affect its fluidity, ultimately affecting the changes in processing methods, such as injection molding grade, extrusion grade, blow molding grade, rolling grade, etc. The main reason why the same resin affects its fluidity is due to its molecular weight and the arrangement of molecular chains, such as linear molecules and body shaped molecules. Among them, high fluidity resins include: PS, HIPS, ABS, PE, PP, PA, etc; Low fluidity resins: PC, MPPO, etc; Non flowing resins: polytetrafluoroethylene, UHMWPE, PPO, etc.

02 Selection of additives

1. Purposive selection of additives

Different types of additives have different target properties, and the additives added to the system can fully fulfill their expected functions and achieve the target specified indicators. Among them, the specified indicators are generally national standards, international standards, or performance requirements proposed by customers. The common performance of target resin modification is as follows.

1) Flame retardancy: inorganic phosphorus, organic halides, organic phosphides, organic silicon and nitrides, etc.

2) Reinforcement: There are two main categories: fibers and whiskers. Glass fiber, asbestos fiber, carbon fiber, whiskers, quartz fiber, graphite fiber, and ceramic fiber, etc; PAN fiber, polyethylene fiber, PA fiber, PC fiber, PVC fiber, and polyester fiber, etc; Boron fibers and metal whiskers such as aluminum, titanium, and calcium.

3) Toughening: High impact resistant resins 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 monomer (EPDM), nitrile rubber (NBR), styrene butadiene rubber, natural rubber, butadiene rubber, chloroprene rubber, polyisobutylene and butadiene rubber, etc.

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

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

2. The influence of the morphology of additives on the composite performance

The same additives have different morphological distributions and their effects on modification are also different. For powdered additives, the key influencing factor is their particle size.

1) The smaller the particle size, the more beneficial it is for the tensile and impact strength of the filling material. For example, in terms of impact strength, for every 1 decrease in the particle size of antimony trioxide μ m. The impact strength will double;

2) The smaller the particle size of the flame retardant, the better the flame retardant effect. For example, adding 4% particle size of 45 to ABS μ Antimony trioxide of m with addition of 1% particle size of 0.03 μ The flame retardant effect of antimony trioxide on m is the same;

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

4) Taking carbon black as an example, the smaller its particle size, the easier it is to form a network of conductive pathways, achieving the same conductive effect. The amount of carbon black added is reduced. But like colorants, there is also a limit to particle size. If the particle size is too small, it is easy to aggregate and difficult to disperse, but the effect is not good.

For fibrous additives, the higher the degree of fiber in the additive, the better the reinforcement effect. Among them, the degree of fibrosis of additives can be expressed by the aspect ratio (L/D). The molten state is more conducive to maintaining the aspect ratio and reducing the probability of fiber breakage than the powdered state, making it a better addition method.

3. Compatibility between additives and resins

The good compatibility between resin and additives is an important foundation for ensuring the good performance of additives, ensuring their durability, extraction resistance, migration resistance, and precipitation resistance during use. Good compatibility is a basic requirement, and even barrier formulations require additives to be distributed layer by layer in the resin. The main methods to improve resin compatibility are:

1) The addition of compatibility additives, such as surfactants, is best achieved in order to maximize their effectiveness.

2) Surface treatment. Using compatibilizers or coupling agents as surface treatment agents to improve the compatibility between resin and additives. Common coupling agents include silanes, titanates, and aluminates; Compatibilizers include maleic anhydride grafted polymers corresponding to the resin. The additives that require 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 performance, but also to establish a low cost based on economic foundation. The requirements for different additives vary: 1) Flame retardants, toughening agents, magnetic powders, barrier agents, etc. Although the more additives added, the better from a performance perspective, the cost must also be determined; 2) Conductive additives generally form circuit paths; 3) An anti-static agent can form a discharge layer on the surface; 4) Coupling agent can form surface coating.

5. The relationship between resin and additives

The addition of additives should not cause the inherent performance of the resin to deteriorate. For example, PPS cannot add additives containing lead and copper, and PC cannot use antimony trioxide, which can lead to depolymerization; Meanwhile, the acidity and alkalinity of the additives should be consistent with that of the resin, otherwise there will be a reaction between the two.

6. The relationship between additives and other components

In a formula, in order to simultaneously achieve multiple objectives, it is necessary to add various different additives. The interaction of additives is very complex, and the main overview is: 1) they are independent of each other and have no effect; 2) Synergistic effect: Multiple additives with heavy formula promote each other, resulting in an overall effect higher than the average of a single additive; 3) Mutual elimination: When two or more additives are added together, the effect is lower than the average value when they are added alone. For example, in anti-aging plastic formulas, sulfur ether co antioxidants and HALS light stabilizers are not used together because the acidic components generated by sulfur ether inhibit the photostability of HALS.

03 Mix evenly

Uniform mixing is a basic requirement for plastic formula modification, and it also requires the formation and uniform distribution of additives in the resin. Uneven distribution of additives not only fails to improve the performance of the original resin, but may also result in poorer performance than pure resin due to uneven distribution of fillers. For example, the use of fillers can affect the mechanical and processing properties of materials due to uneven dispersion, which not only significantly reduces the mechanical properties but also affects the processing performance. Common ways to improve the uniform mixing of additives: 1) Reasonably sort the added fillers, such as: during the coupling treatment process, the fillers are advanced, heated and dehydrated, and then the coupling agent is added; 2) The components should be added to the system in primary and secondary order, and large batches of fillers can be added in multiple batches to facilitate uniform mixing. Coupling agent treatment generally requires three sprays to disperse evenly and achieve good coupling effect.

04 Selection of Formula

Formula processability refers to the processability of modified plastic formulas, which meet the requirements of both modified plastic and product molding. The main manifestation of the processability of the formula is that the auxiliary agent has good heat resistance, does not undergo evaporation loss, decomposition and deactivation; The formed formula has minimal wear and corrosion on the equipment, and releases non-toxic gases, all of which can be used as assessment criteria.

1. The flowability of modified plastics

The fluidity of plastics is the main aspect that affects the processing performance of plastics, and it is also an important basis for choosing which plastic processing method to use. Generally speaking, the addition of inorganic fillers will lead to a decrease in flow performance, and it is necessary to add flow modifiers for optimization.

2. Heat resistance

The heat resistance is considered in two aspects: 1) reduce the processing temperature of the resin, and the processing temperature should not exceed the decomposition temperature of the additives to ensure the stable existence of the additives and reflect the modification performance; 2) Add a certain amount of antioxidant additives to prevent thermal decomposition and affect the performance of the resin. Generally speaking, most organic dyes have low decomposition temperatures and are not suitable for high-temperature processing of engineering plastics; The decomposition temperature of spices is generally below 150 ℃, and only low processing temperature resins such as EVA can be used as carriers.

3. The environmental friendliness of the formula

The environmental friendliness of the formula includes being harmless to the human body, equipment, environment, and users. Human hygiene - The resin and selected additives should be absolutely non-toxic, or their content should be controlled within the specified range. Environmental pollution - The selected components cannot pollute the environment.

4. Cost price and source

The plastic modification formula pursues the lower the price, the better. During the implementation process, the use of additives should follow the following principles:

1) Prioritize the use of low-priced raw materials;

2) Prioritize the use of existing raw materials: no need for procurement, stable sources, and clear performance;

3) Priority use of domestic raw materials: Price fluctuations are less affected by foreign exchange, trade policies, etc;

4) Prioritize the use of nearby raw materials: reduce the cost of inventory;

5) Priority should be given to using universal raw materials: with a wide range of sources and relatively stable performance.

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