Plastic modification methods and technical parameters

Time:2021-08-19 11:52:23 / Popularity: / Source:

Plastic modification methods and technical parameters 

1, masterbatch core

Amount of masterbatch nucleus in masterbatch is generally more than 20%.

2, dispersant

Its function is to have good compatibility between filler and carrier tree, melting point and melt viscosity should be lower than that of carrier resin. Common dispersants include stearic acid and its salts, erucamide, solid paraffin, liquid paraffin, polyethylene wax (polyethylene with relative molecular weight), oxidized PE, and α-methylstyrene. Dispersant has a low melting point and can melt rapidly when temperature rises, it is coated on the surface of inorganic filler treated with coupling agent and crosslinking agent. Surface tension of masterbatch is closer to that of main resin, thus greatly improving dispersibility of inorganic filler, can reduce viscosity of composite material and improve fluidity. General dosage is about 5%.

3, carrier resin

Whether filler masterbatch can be uniformly dispersed in main resin depends on choice of carrier resin. Atactic polypropylene has low soft point, good coating effect on calcium carbonate and other particles, melt flow rate of filler masterbatch is very high. Dispersion of masterbatch in main resin is very good, but it has a greater impact on mechanical properties of product and cannot meet better requirements of product.
Since filler masterbatch is mainly used for processing of polyolefin plastic products such as polyethylene or polypropylene, available carrier resins mainly include LDPE, PS, EVA, CPE, etc., but HDPE, PP, PS are used alone as filler masterbatch for carrier resin production. Material strip is relatively brittle, not easy to cut (particles are fragile). Flow rate of LLDPE melt is low, masterbatch made is not easy to disperse.

4, ABS plastic vs. PVC

ABS plastic can significantly enhance impact strength of PVC, but has a small decrease in tensile strength. Some varieties have function of processing aids, and general dosage is 5 to 15 parts. Due to different composition and relative molecular weight of ABS, modification effect is often different.

5, ABS plastic and MBS plastic

Both ABS plastic and MBS plastic are effective impact modifiers for PVC. Main difference is that the former is mainly used for extruding pipes, profiles, calendering and blow molding bottles. It should be noted that this type of modified polymer has unsaturated double bond structure of butadiene in its components, so weather resistance of blending with PVC is poor, and light stabilizers should be added to formulation. Both are very toxic and can be used in food contact occasions.

6, CPE

CPE generally has a chlorine content of 20% to 50%, and a chlorine content greater than 25% is non-flammable. CPE modified PVC, the biggest feature is good weather resistance, it is generally believed that variety with 36% chlorine content has the best modification effect in rigid PVC, can obtain good processability, dispersion and impact resistance. Varieties with chlorine content below 25% are not compatible with PVCD. Main disadvantages of CPE are poor transparency of its products, low tensile strength, and surface gloss of products is not as good as that of pure PVC products. In addition, pores of CPE pellets are higher than that of PVC, and there is more entrapment gas. During processing, special attention should be paid to venting. It is best to use a vented extruder during extrusion.

7. PVC

Due to difference in shell and core composition, number of layers, there are countless varieties, so for rigid PVC products, it is the most successful transparency (processing or impact) changer developed after MBS.
A. Modification effect of impact type ACR
b. Improve impact strength of rigid PVC materials. With increase in amount of ACR added, impact strength of rigid PVC gradually rises, especially in the range of 5-10 parts, impact strength changes the fastest, and at 10 parts, it basically reaches peak. After that, increasing amount of ACR has no obvious effect.
C. As amount of ACR added in blend increases, melting and plasticizing time is shortened. ACR has effect of promoting gelation and plasticization of PVC resin. PVC with ACR has a significant increase in extrusion expansion than PVC without ACR. General dosage of ACR201 is 1~3 servings.

8, EVA plastic raw material modified plastic PVC plastic

Varieties of EVA modified plastic PVC are mostly ternary EVA copolymers, such as ethylene-vinyl acetate-carbon oxide (E-VA-CO). Blending compatibility of the two is very good, and it acts as a polymer plasticizer. It has excellent durability and is used in industries such as building materials, automobiles, boots and shoes.

9. PVC plastic and cyanide butadiene rubber (NBR)

PVC plastic and cyanide butadiene rubber (NBR) have good compatibility, but compatibility of the two is extremely affected by acrylonitrile (AN) in NBR. When AN content in NBR is about 20%, impact strength of its blend with PVC is the highest.

10, PA plastic and PP plastic blend

PA plastics and PP plastics are blended, addition of compatibilizers increases, mechanical properties of blends are improved, indicating that amount of graft copolymers added in a certain range is large, and chemical reactions generated at two interfaces are correspondingly large, compatibility of PA and PP is better. However, when graft copolymer exceeds 6.25%, performance decreases instead.

11. CPE

CPE (with a chlorine content of 36%) can be used as a compatibilizer for PVC and PE blends. For example, adding 15% to 25% of CPE in a PVC/PE/PP blend system (30:28:42) can achieve better blending results.

12. Natural rubber and PE blend

In blending system of natural rubber and PE, due to interpenetration between non-crystalline part of PE and non-crystalline natural rubber, mechanical properties are poor. If 6% of two block copolymer (NR-b-PE) is added, compatibility of the two is improved, reduction of interfacial tension is reduction of size of dispersion of PE.

13. Compatibilizer

Under premise of fully saturating the entire interface of blend, amount of compatibilizer is as small as possible, and usual amount is less than 20%.

14. Reactive compatibilizer

Reactive compatibilizers mostly contain acid-based, epoxy-based, isocyanate-based and vinyl-based, etc., which form new chemical bonds with blended polymer components, which are also called chemical compatibilizers. It is especially suitable for blending of polymers with poor compatibility and reactive functional groups. There are mainly carboxylated PE, carboxylated PP, carboxylated PS, etc. They are designed to promote compatibility of non-polar polymers (PE, PP, PS, etc.) with polar polymer polyamide (PA) . Question: What is reaction type, reaction mechanism, and specific reaction content ofreactive compatibilizer? Mainly include maleic anhydride grafting, acrylic acid grafting, and sulfonation treatment.

15. Classification of plastic flame retardant grades

Flame retardant grades of plastics increase gradually from HB, V-2, V-1 to V-0:
HB: UL94 and CSA C22.2 No 0.17 standard in the lowest flame retardant grade. It is required that for samples with a thickness of 3 to 13 mm, burning rate is less than 40 mm per minute; for samples with a thickness of less than 3 mm, burning rate is less than 70 mm per minute; or extinguished before 100 mm mark.
V-2: After two 10-second burning tests are performed on sample, flame goes out within 60 seconds. There may be burning materials falling.
V-1: After sample is subjected to two 10-second burning tests, flame is extinguished within 60 seconds. No burning objects can fall.
V-0: After sample is subjected to two 10-second burning tests, flame is extinguished within 30 seconds. No burning objects can fall.

16. Pay attention to some conventional precautions for dyeing modified plastics:

1. PS coloring formula
PS is a colorless and transparent plastic. Its coloring is mainly to make full use of its excellent coloring performance to make various beautiful parts. Sharpness, transparency and heat resistance of coloring agent should be emphasized. Since general colors migrate for a long time in PS, there is a wide range of solid colorants to choose from.
2. PVC coloring formula
There are several factors that affect coloring of PVC. The first is that PVC is decomposed by heat to release HCL, so a heat stabilizer should be added to formula. Secondly, in order to reduce cost, fillers are often added. Type and amount of these additives have a great impact on color change; again, soft and hard products, especially plasticizer added to the former, will also make color change greatly. This should be fully understood and valued.

17. There are some shortcomings in using titanate coupling agent:

1. Higher cost
2. Titanate is prone to form darker compounds due to its own oxidation or with certain antioxidants in polyolefins, which affects whiteness of calcium carbonate and makes master batch gray.
3. Calcium carbonate treated with titanate coupling agent, during storage or processing, lipophilic end of titanate molecule is prone to hydrolysis or alcoholysis and lose its function. Optimal amount of titanate is determined through experiments according to nature of filler and purpose of product. In general, recommended amount is 0.5%-3% of filler.

18. Aluminate coupling agent

It can improve dispersibility of various fillers and pigments, and vividness of pigments. Since it has a lighter color, it can increase organic film of fillers such as calcium carbonate. Thermal stability is better than titanate, it can play a chemical role on the surface of filler, can produce adhesion and crosslinking at interface. Amount of titanate coupling agent is generally 0.5%~2.5% of filler. For fillers with high specific surface area or active surface such as carbon black, alumina, etc., amount can be increased to 1.5%~2.5%. Aluminate coupling agent can be used together with titanate coupling agent to produce synergistic effects, improve performance and reduce costs.

19, titanate

Amount of titanate is calculated as percentage of filler. Optimal amount in the process of modifying plastic should be determined through experiments according to nature of filler and purpose of product. In general, recommended amount is 0.5% to 3%.

20, aluminate

General dosage of aluminate is 0.25~0.5 parts. It can be used together with tribasic lead sulfate and dibasic lead phosphite, which has a synergistic and stabilizing effect. It also has a certain lubricating effect on PVC, and surface finish of product is improved. Aluminate coupling agent is cheap, can reduce cost of formulation, can also be used in formulations of PE, PP, PU, PS, etc.

21. MBS modified plastic PVC

Amount of MBS modified plastic PVC is usually maintained at 10%~15%. And MBS modified PVC is generally a transparent product.

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