The density, hardness, and gloss of the plastic can be reduced or increased by appropriate methods to reduce or increase the plastic’s initial relative density, increase the hardness or increase the flexibility, and change the gloss to meet the needs of different applications.
1. How to reduce the density of plastic?
Reducing plastic density refers to lowering the plastic’s initial relative density through appropriate methods to meet different applications’ needs. There are three methods to reduce plastics’ density: foaming modification, adding lightweight fillers, and blending light resins.
1. Foaming modification
The foam molding of plastic products is the most effective way to reduce its density. The two modification methods of adding lightweight additives and blending light resins can only mitigate the density slightly, and the decrease is generally only about 50%. The lowest relative density can only reach about 0.5. The thickness of plastic foam products can vary widely, and the relative density can get as low as 10-3. At present, our everyday PVC foam products include PVC foam board, PVC foam shoe sole, PVC foam tube, PVC foam profile, PVC wood plastic foam products (moving door panel, door line, wall panel, etc.), PVC hair Soak floor mats and so on.
2. Add light filler
Such as PE, PP, CPE, ABS, MBS, such as wood flour, hollow glass beads, etc.; such as the microstructure of microbead fillers, this method makes the density reduction relatively small. Generally, the lowest relative density can reduce to about 0.4-0.5. The relative density of fillers is mostly higher than that of plastics, and there are only the following types of stuffing with lower relative density than plastics. The better fill is calcined clay, which has a smaller specific gravity than calcium powder. The price is not much different from that of light calcium, and the oil absorption value is equivalent to that of calcium powder.
- The relative density of glass hollow microspheres (floating beads) is 0.4-0.7, mainly used for thermosetting resins;
- The relative density of phenolic microbeads is 0.1.
2) Organic fillers
- The relative density of cork powder is 0.5, and the apparent viscosity is 0.05—0.06;
- The relative density of fiber dust and cotton dust is 0.2-0.3;
- Fruit husk crops such as rice straw powder, peanut powder, and coconut husk powder.
- Such as plasticizers, liquid internal and external lubricants, etc., the density of pure polyvinyl chloride is 1.4g/cm3, and plasticized polyvinyl chloride (containing approximately 40% plasticizer) is 1.19~1.35;
3. Blending of lightweight materials
Add low-density plastic blends, such as PE, PP, CPE, ABS, MBS; there is also a kind of lightweight filler: wood flour, which is the fine fiber of the wood, which is very light. But there are certain limitations, according to your Use different methods.
2. How to increase the density of plastics?
Increasing the plastic’s density is a way to increase the relative density of the original resin, mainly by adding heavy fillers and blending heavy resins.
1. Add heavy filler
- Metal powder
- Heavy mineral filler
2. Blending heavy resin
This method has a relatively small improvement and generally can only reach about 50% at the highest. It is mainly suitable for some light resins such as PE, PP, PS, EVA, PA1010, and PPO, etc. Heavy resins often added are PTFE, FEP, PPS, and POM, etc.
3. How to change the hardness of plastic?
1. The concept and representation of hardness
Hardness refers to a material’s ability to resist other more complex objects press into its surface.
The hardness value is a conditional quantitative reflection that characterizes the hardness of the material. It is not a pure and definite physical quantity. The size of the hardness value not only depends on the material itself but also depends on the test conditions and measurement methods. With different hardness measurement methods, the hardness value measured for the same material is not the same. Therefore, to compare the hardness between materials, the same measurement method’s hardness value must be used for comparability.
There are several methods commonly used to express hardness:
- Shore hardness
- Rockwell hardness
- Mohs hardness
2. Blending improves the hardness of plastics
The plastic blending improvement method is to blend high-hardness resin with low-hardness resin to increase its overall hardness. Standard blended resins are PS, PMMA, ABS, and MF, etc. The resins that need to be modified are mainly PE, PA, PTFE, and PP.
3. Compound to improve the hardness of plastic
The method of plastic compounding to improve the hardness is to compound a layer of high-hardness resin on low-hardness plastic products’ surfaces. This method is mainly suitable for extruding products, such as plates, sheets, films, and pipes. Commonly used composite resins are PS, PMMA, ABS, and MF.
4. Improved surface hardness of plastics
This method refers to only improving the plastic product’s external hardness, while the internal hardness of the product remains unchanged. This is a low-cost hardness improvement method.
This modification method mainly uses for housings, decorative materials, optical materials, and daily necessities. This modification method includes explicitly three methods: coating, plating, and surface treatment.
4.How to improve the flexibility of plastics?
Intuitively speaking, plastic’s flexibility refers to the softness of plastic products. That is, the softer the plastic product, the better its flexibility. In polymer physics, flexibility defines as the property of polymer chains that can change their uniformity. The flexibility of a plastic depends on the molecular chain structure of its polymer.
1. Add plasticizer
Plasticizer refers to a class of substances that can improve the plasticity of polymers. It mainly uses for PVC resin. The amount of plasticizer in PVC can account for more than 98% of the total amount of plasticizer. In addition to PVC, plasticizers also use in polymers such as PVDC, CPE, SBS, polyvinyl acetate, nitrocellulose, PA, ABS, and PVA.
2. The main functions of plasticizers are as follows:
- Reduce the melting temperature and melt viscosity of the polymer, thereby reducing its molding processing temperature.
- Make polymer products that have softness, elasticity, and low-temperature resistance.
3.The specific mechanism of action of the plasticizer is as follows:
- Volume effect
- Shielding effect
5.Improve plastic gloss
There are two ways to improve the gloss of plastics. One is to improve the surface gloss of plastic products, which call brightening modification; the other is to reduce plastic products’ surface gloss, called matting modification.
Brightening of plastics means improving the surface gloss or finish of plastic products. Besides the reasonable selection of raw materials, the specific methods include adding the brightening method, blending the brightening method, shape control brightening method, molding equipment smoothness control, two Sub-processing brightness enhancement method, and surface coating brightness enhancement method, etc.
The following mainly introduces the brightening method of plastic:
1. Selection of plastic raw materials
The reasonable selection of plastic raw materials is the most fundamental factor to improve the surface finish of plastic products. If the raw materials are selected well, it is easy to improve the gloss; otherwise, it is more complicated.
Plastic raw materials can divide into two categories: resins and additives.
2. The choice of resin
The resin’s characteristics have a more significant impact on the surface gloss of plastic products, and it is the most effective way to control the surface gloss of plastic products. Its influence on the surface gloss of related plastic products mainly depends on the following aspects:
1) Variety of resin
The gloss of the related products of different resin varieties is quite different. It generally considers that the glow of the following resins’ related products is better: melamine resin, ABS, PP, HIPS, PE, POM, PMMA, and PPO, etc., among which melamine resin and ABS two kinds of gloss are the most outstanding.
For the same resin, the synthesis method is different, and the gloss of the resin corresponding to the product is also further. E.g.:
- For PP, the glossiness of different types synthesized by other polymerization methods is as follows: PP-R>homopolymer PP>block copolymer PP.
- For PE, the gloss of three different varieties is as follows: LDPE>LLDPE>HDPE
- For PVC, emulsion PVC resin has a higher luster than suspension PVC resin.
- For PS resin, the brilliance of high-impact polystyrene (HIPS) is greater than that of general-purpose polystyrene (GPPS)
2) Characteristics of resin
The specific characteristics are different, and the gloss is also other. Among the features of the resin, the factors that affect the glow.
- Generally, the greater the melt flow rate (MFR), the greater the gloss of the related product.
- The influence of molecular weight is mainly reflected in the width of molecular weight distribution. The wider the molecular weight distribution, the lower the gloss of the related products. This is because the molecular weight distribution is comprehensive, and the irregularity of the material has increased.
- The influence of water absorption The resin with high water absorption has a more significant impact on its related products’ gloss. For example, PA, PI, PSF, and PC with ester group (-COOR) and galantamine group (-CONH2) in the molecule, if it is not dried or dried incompletely, water ripples, bubbles, and silver wires will be produced on the surface of the product. , Markings, blemishes, etc., so that the surface gloss is significantly reduced.
3. Selection of additives
Among all plastic additives, fillers have the most significant impact on gloss, followed by plasticizers, stabilizers, and flame retardants, but the effect is relatively small. The influence of fillers on a gloss can divide into the following aspects:
1) Type of filler
Different fillers have different effects on gloss. Except for glass microbeads, almost all fillers will reduce the glow of filled products, but the decline is additional.
The influence of several fillers on the gloss of filled products is as follows: metal salt>glass fiber<talc powder<mica.
2) The shape of the filler
Different microscopic shapes of filler particles have other effects on the gloss of the filled products. The order of the magnitude of the impact is spherical <granular <needle-like <flake.
3) The particle size of the filler
The smaller the filler’s particle size, the smaller the decrease in the filler product’s gloss. Also, the filler particle size’s distribution width is different, and the effect on the glow of the filled product is also different. The influence law is the more comprehensive the filler particle size distribution, the lower the surface gloss of the supplied product. This is mainly because the more significant the filler’s particle size range, the more uneven the filled product’s surface, the more likely the incident light can produce a diffuse reflection.
4) Filling amount of filler
The filling of the filler increases and the surface gloss of the filled product decreases. Taking the CaCO3 served PP system as an example, when the CaCO3 filling amount is 5%, the supplied product’s surface gloss is 50%. When the CaCO3 filling amount is 15%, the gloss of the filling drops to 32%.