Five basic methods for adjusting the density and hardness of pvc, pe, and pp products

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1. How to reduce the density of plastic?

Reducing the density of plastics means that the relative density of the plastics is reduced by appropriate means to suit the needs of different applications.

The methods for reducing the density of plastics include foaming modification, adding lightweight fillers, and blending lightweight resins.

1. Foaming modification

Foam molding of plastic products is the most effective way to reduce their density. The addition of light addition materials and blending of light resin can only reduce the density by a small amount, and the reduction is generally only about 50%, and the lowest relative density can only reach about 0.5. Plastic foamed products vary widely in density and have a relative density of 10-3. At present, our common PVC foaming products include PVC foam board, PVC foam sole, PVC foam tube, PVC foam profile, PVC wood plastic foam product (sliding door panel, door sleeve line, wall panel, etc.), PVC hair Soaking mats, etc.

2. Add light fillers, such as PE, PP, CPE, ABS, MBS; such as wood powder, hollow glass beads, etc.; such as micro-bead filler microstructure, this method makes the density reduction is relatively small, generally the lowest can be reduced The relative density is about 0.4-0.5. The relative density of the fillers is larger than that of plastics, and the types of fillers with a relatively low density of plastics are only as follows. In addition, the filler is better in calcined clay, the specific gravity is smaller than that of calcium powder, and the price is not much different from that of light calcium. The oil absorption value is equivalent to that of calcium powder.

1) Microbeads

a. Glass hollow microspheres (drift beads) with a relative density of 0.4-0.7, mainly used for thermosetting resins;

b. The relative density of the phenolic microbeads is 0.1.

2) Organic fillers

a. Cork powder has a relative density of 0.5 and an apparent density of 0.05-0.06;

b. The relative density of fiber dust and cotton chips is 0.2-0.3;

c. Fruit shell crops such as straw flour, peanut flour and coconut shell powder.

d, such as plasticizer, liquid internal and external lubricants, etc., the density of pure polyvinyl chloride is 1.4g / cm3, plasticized polyvinyl chloride (about 40% plasticizer) is 1.19 ~ 1.35;

3. Blending lightweight materials

Add low-density plastic blends, such as PE, PP, CPE, ABS, MBS; there is also a lightweight filler: wood flour, which is fine fiber of wood, very light. But there are certain limitations, according to Use different methods yourself.

2. How to increase the density of plastics?

Increasing the density of plastics is one way to increase the relative density of the original resin, mainly by adding heavy fillers and blending heavy resins.

1. Add heavy fillers including:

(1) Metal powder

(2) Heavy mineral filler

2. Blending heavy resin

This method is relatively small, and generally can only reach about 50%. Mainly suitable for some light resins such as PE, PP, PS, EVA, PA1010 and PPO. Heavy resins that are often added include: PTFE, FEP, PPS, and POM.

How to change the hardness of plastic?

1. The concept and representation of hardness

Hardness refers to the ability of a material to resist the pressing of other hard objects into its surface.

The magnitude of the hardness value is a conditional quantitative representation of the degree of softness and hardness of the material. It is not a purely defined physical quantity. The hardness value depends not only on the material itself, but also on the test conditions and the measurement method, that is, the different hardness measurement methods, and the hardness values ​​measured for the same material are not the same. Therefore, to compare the hardness between materials, the hardness values ​​measured by the same measurement method must be comparable.

The methods commonly used to indicate hardness are as follows:

a. Shore hardness

b. Rockwell hardness

c. Mohs hardness

2. Blending to improve the hardness of plastics

An improved method of plastic blending is to blend a high hardness resin in a low hardness resin to increase its overall hardness. Common blending resins are: PS, PMMA, ABS and MF, etc. The resins to be modified are mainly PE, PA, PTFE and PP.

3. Composite improved plastic hardness

The method of improving the hardness of the plastic composite is to combine a high hardness resin on the surface of the low hardness plastic product. This method is mainly suitable for extrusion products such as plates, sheets, films and pipes. Commonly used composite resins are PS, PMMA, ABS and MF.

4. Plastic surface hardness improvement

The method refers to only improving the hardness of the appearance of the plastic product, and the hardness inside the product is unchanged. This is a low cost hardness improvement method.

This modification method is mainly used for housings, decorative materials, optical materials, and daily necessities. This modification method mainly includes three methods of coating, plating and surface treatment.

How to improve the flexibility of plastics?

PVC hose

Intuitively, the flexibility of plastic refers to the softness of plastic products, that is, the softer the plastic products, the better the flexibility. In polymer physics, flexibility is defined as the property of a polymer chain to change its uniformity. The flexibility of a plastic depends on the molecular chain structure of its polymer.

1. Add plasticizer

Plasticizer refers to a kind of substance which can improve the plasticity of polymer. It is mainly used for PVC resin. The amount of PVC can be more than 98% of the total amount of plasticizer. In addition to PVC, plasticizers are also used in polymers such as PVDC, CPE, SBS, polyvinyl acetate, nitrocellulose, PA, ABS and PVA.

2. The main effects of plasticizers are as follows:

a. Reduce the melting temperature of the polymer and the viscosity of the melt, thereby reducing the molding processing temperature.

b. The polymer article has softness, elasticity and low temperature resistance.

3. The specific mechanism of action of plasticizers is as follows:

Volume effect

b. Shielding effect

V. Improve the gloss of plastics

High gloss plastic

The method for improving the gloss of plastics includes two aspects, one is to improve the surface gloss of the plastic product, which is called brightening modification; the other is to reduce the surface gloss of the plastic product, which is called extinction modification. The following mainly introduces the brightening method of plastic:

The brightening of the plastic enhances the surface gloss or finish of the plastic product. In addition to the reasonable selection of the raw materials, the addition method includes a brightening method, a blending brightening method, a form control brightening method, and a control of the finishing condition of the molding equipment. Sub-processing brightening method and surface coating brightening method.

1. Selection of plastic raw materials

Reasonable selection of plastic raw materials is the most basic factor to improve the surface finish of plastic products. If the raw materials are selected well, the gloss is easy to be improved; otherwise, it is more difficult.

Plastic raw materials can be divided into two major categories of resins and additives.

2. Resin selection

The characteristics of the resin itself have a great influence on the surface gloss of the plastic product, and are the most effective method for controlling the surface gloss of the plastic product. Its influence on the surface gloss of the corresponding plastic products mainly depends on the following aspects:

1) Variety of resin

The gloss of different resin varieties is quite different. It is generally believed that the gloss of the corresponding resin is better: melamine resin, ABS, PP, HIPS, PA, POM, PMMA and PPO, among which melamine resin and ABS has the most outstanding gloss.

For the same resin, the synthesis method is different, and the gloss of the resin corresponding to the product is also different. E.g:

a. For PP, the gloss of the synthetic varieties of different polymerization methods is as follows: PP-R> homopolymer PP> block copolymerized PP.

b. For PE, the glossiness of three different varieties is as follows: LDPE>LLDPE>HDPE

c. For PVC, the emulsion method PVC resin has higher gloss than the suspension method PVC resin.

d. For PS resin, high impact polystyrene (HIPS) gloss is greater than general purpose polystyrene (GPPS)

2) Characteristics of the resin

For the same resin. The specific characteristics are different, and the gloss is also different. The characteristics which affect the gloss in the properties of the resin are mainly as follows.

a. The greater the melt flow rate (MFR), the greater the gloss of the corresponding article.

b. Influence of molecular weight The influence of molecular weight is mainly reflected in the width of molecular weight distribution. The broader the molecular weight distribution, the lower the gloss of the corresponding article. This is mainly because the molecular weight distribution is wide and the irregularity of the material is increased.

c. Effect of water absorption rate The resin with high water absorption rate has a great influence on the gloss of its corresponding products. For example, PA, PI, PSF, PC, etc. containing ester groups (-COOR) and guanamine groups (-CONH2) in the molecule, if not dried or dried thoroughly, will produce water ripples, bubbles, and silver on the surface of the product. , markings, edulis, etc., so that the surface gloss is greatly reduced.

3. Selection of additives

Among all the additives for plastics, the filler has the greatest influence on the gloss; secondly, there are plasticizers, stabilizers and flame retardants, but the effect is small.

Effect of filler

The effect of filler on gloss can be divided into the following aspects:

a, the variety of fillers

Different filler types have different effects on gloss. Almost all fillers except glass beads reduce the gloss of the filled product, but only in different degrees.

The order of influence of several fillers on the gloss of filled products is as follows: metal salt>glass fiber

b, the shape of the filler

The microscopic shape of the filler particles is different, and the influence on the gloss of the filled product is also different. The order of influence is: spherical

c, the particle size of the filler

The smaller the particle size of the filler, the less the gloss of the filler product is reduced. In addition, the distribution width of the filler particle size is different, and the influence on the gloss of the filled product is also different. The influence law is: the wider the particle size distribution of the filler, the lower the surface gloss of the filled product. This is mainly because the larger the difference in the particle size range of the filler, the more uneven the surface of the filled product, and the more easily the incident light is diffusely reflected.

d, the filling amount of the filler

The filling of the filler is increased, and the surface gloss of the filled article is lowered. Taking the CaCO3 filled PP system as an example, when the CaCO3 loading amount is 5%, the surface gloss of the filled product is 50%. When the CaCO3 loading was 15%, the gloss of the filler decreased to 32%.

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