CN110330594A - Method for modifying polyethylene by crosslinking - Google Patents

Abstract

The invention belongs to the technical field of material modification, and discloses a method for crosslinking and modifying polyethylene. The method for crosslinking and modifying polyethylene is the silane crosslinking method of PE. The silane crosslinked PE uses PE as the base resin. Silane is a bridge material, which forms chemical covalent bonds between polymer macromolecular chains to replace the original van der Waals force, making the molecules form a three-dimensional network. The preparation of silane crosslinked PE includes two stages of grafting and crosslinking. The present invention adopts the silane cross-linking method, which does not require expensive equipment investment, can obtain higher extrusion speed, and can reduce the waste generated during the start-up stage, and the aging resistance of the cross-linked polyethylene is better than other preparation methods. The technically simple and stable silane crosslinking method can be applied to a wide range of composite processing.

Description

A kind of method of polyethylene cross-linking modification

technical field

The invention belongs to the technical field of material modification, and in particular relates to a method for cross-linking modification of polyethylene.

Background technique

At present, the existing technologies commonly used in the industry are as follows: modern plastics have very excellent physical properties, but are only affected by their relatively poor heat resistance, and their service life is still limited in many application fields. Due to its structural characteristics, PE It cannot withstand high operating temperature, and its low mechanical strength limits its application in many fields. In order to improve the heat resistance and mechanical properties of PE, an effective method is to modify it by cross-linking.

For cross-linked polyethylene, it is precisely because of its unique three-dimensional network molecular structure that it has more excellent performance. Cross-linked polyethylene is widely used in the pipe manufacturing industry due to its excellent mechanical processing properties, and gradually replaces non-cross-linked plastic pipes such as polypropylene, polyvinyl chloride and various thermoplastic polyethylenes. In more demanding applications, such as in the automotive industry, XLPE can be used as an alternative to more expensive engineering plastics. The application of cross-linked polyethylene foam in the automotive field, the main uses include automotive interior roofing, luggage, floor mats, side panels, heat insulation pads, door inner guards, waterproof curtains, sun visors, waxing plates, air conditioning systems Wait. At present, there are many cross-linking modification methods for polyethylene, but the modification often needs to invest in expensive equipment, the technology is more complicated, more waste materials are generated, and greater economic losses are caused.

To sum up, the problems existing in the prior art are: at present, expensive equipment needs to be invested in the modification of polyethylene, the technology is more complicated, more wastes are produced, and greater economic losses are caused.

Contents of the invention

Aiming at the problems in the prior art, the invention provides a method for crosslinking and modifying polyethylene.

The present invention is achieved in this way, a polyethylene cross-linking modification method is: PE silane cross-linking method, silane cross-linked PE with PE as the base resin, with silane as the bridge material, in the polymer macromolecule A chemical covalent bond is formed between the chains to replace the original van der Waals force, so that the molecules form a three-dimensional network. The preparation of silane cross-linked PE includes two stages of grafting and cross-linking.

Grafting stage: The peroxide initiator is decomposed by heat to form primary free radicals, which capture the H atoms on the PE macromolecular chain to form PE macromolecular free radicals, which are combined with vinyltrialkoxysilane CH ₂ =CH _—The vinyl group in Si (OR) ₃ undergoes an addition reaction to form a PE-grafted silane active macromolecule. The active macromolecule realizes chain transfer by capturing the H atom in PE to obtain a PE-grafted silane product, namely grafting Material A;

Crosslinking stage: PE grafted silane products are hydrolyzed under the action of organotin catalysts to generate silanols, and silanols are dehydrated or dealcoholized to form PE silane crosslinked products.

Further, the base resin is a homopolymer or copolymer of olefin after drying treatment.

Further, the initiator is DCP, and the amount of DCP is 0.05-0.5 parts.

Further, the cross-linking agent adopts ethylenically unsaturated silane, and the dosage of the cross-linking agent is between 0.5-4 parts.

Further, the antioxidants are antioxidant 330, 168, 1010, RD and other aromatic amine stabilizers, and compound antioxidants can also be used, and the antioxidant content is not more than 1 part.

Further, the crosslinking catalyst is dibutyltin dilaurate, and its consumption is share.

Further, the polymerization inhibitor is added into a complex polymerization inhibitor during the grafting process.

To sum up, the advantages and positive effects of the present invention are: the present invention adopts the method of silane cross-linking, which does not require expensive equipment investment, can obtain higher extrusion speed, and can reduce the waste generated during the start-up stage, and its cross-linking The aging resistance of polyethylene is superior to other preparation methods, and the simple and stable silane crosslinking method can be applied to a wide range of composite processing.

Description of drawings

Fig. 1 is a flow chart of the preparation method of silane crosslinked PE provided by the embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with the examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The application principle of the present invention will be described in detail below in conjunction with the accompanying drawings.

The method for cross-linking modification of polyethylene provided in the embodiments of the present invention is: silane cross-linking method of PE, silane cross-linked PE uses PE as the base resin, and silane is used as the bridging material to form between polymer macromolecular chains. Chemical covalent bonds are used to replace the original van der Waals force, so that the molecules form a three-dimensional network. The preparation of silane cross-linked PE includes two stages of grafting and cross-linking (as shown in Figure 1).

S101: Grafting stage: The peroxide initiator is decomposed by heat to form a primary free radical, which captures the H atom on the PE macromolecular chain to form a PE macromolecular free radical, which is combined with vinyltrialkoxysilane CH ₂ The vinyl group in =CH—S _i (OR) ₃ undergoes an addition reaction to form a PE-grafted silane active macromolecule, and the active macromolecule realizes chain transfer by capturing the H atom in PE to obtain a PE-grafted silane product, namely Grafting material A.

S102: Cross-linking stage: the PE grafted silane product is hydrolyzed under the action of an organotin catalyst to generate silanol, and the silanol is dehydrated or dealcoholized to form a PE silane cross-linked product.

The base resins provided in the embodiments of the present invention are homopolymers and copolymers of olefins after drying treatment.

The initiator provided in the embodiment of the present invention is DCP, and the dosage of DCP is 0.05-0.5 parts.

The cross-linking agent provided in the embodiment of the present invention adopts vinyl unsaturated silane, and the dosage of the cross-linking agent is between 0.5-4 parts.

The antioxidants provided in the examples of the present invention are antioxidant 330, 168, 1010, RD and other aromatic amine stabilizers. Compound antioxidants can also be used, and the antioxidant content is not more than 1 part.

The cross-linking catalyst provided in the embodiment of the present invention is dibutyltin dilaurate, and its dosage is 0.02-0.15 parts.

In the polymerization inhibitor provided in the embodiment of the present invention, a complex polymerization inhibitor is added during the grafting process.

The present invention will be further described below in conjunction with specific embodiments.

Example 1

Factors affecting silane grafted cross-linked PE are:

Base resin: Homopolymers and copolymers of olefins can be grafted and cross-linked by unsaturated silanes. Due to their different structures, different PEs have different degrees of decrease in melt flow rate before and after grafting. In specific production, it is difficult for a single resin to meet the comprehensive performance requirements, and the method of blending several resins is usually used to adjust the basic characteristics of the resin in order to achieve the expected PE cross-linked products. In addition, silane grafting has strict requirements on the water content of the polymer. When silane encounters moisture in the polymer, it will be hydrolyzed and pre-crosslinked, which will seriously affect the quality of the product. Therefore, the polymer should be dried before use.

Initiator: The commonly used initiator for silane grafting and crosslinking PE is DCP, whose decomposition temperature and half-life can meet the conditions of melt grafting reaction between PE resin and organosilicon monomer. When other conditions are constant, the PE grafting efficiency changes with the increase of DCP dosage. The dosage of DCP is generally 0.05-0.5 parts.

Crosslinking agent: The crosslinking agent generally uses vinyl unsaturated silane as the crosslinking agent, including vinyltrimethoxysilane and vinyltriethoxysilane. The dosage of crosslinking agent is generally between 0.5-4 parts.

Antioxidant: If the antioxidant is added before grafting, it will have a significant impact on the silane grafting reaction, especially the free radical scavenger type antioxidant, because they will capture PE free radicals and inhibit the grafting reaction . Therefore, the addition of antioxidants in the grafting process should be cautious, and appropriate antioxidants should be selected. Commonly used antioxidants include antioxidant 330, 168, 1010, RD and other aromatic amine stabilizers, and compound antioxidants can also be used. Generally, the antioxidant content is not more than 1 part.

Cross-linking catalyst: The most commonly used catalyst for cross-linking catalyst is dibutyltin dilaurate (DBDTL), and its dosage is share. There are generally two forms of adding cross-linking catalysts, one is directly added to PE material or added in the form of masterbatch; the other is to coat a layer of catalyst on the outer surface of the product, the first method is used more.

Polymerization inhibitor: In the process of silane grafting and crosslinking, polymerization inhibitors inevitably have many side reactions. These side reactions are unfavorable to the processing and storage of crosslinked PE, so the occurrence of such reactions should be minimized. In order to reduce these side reactions, the approach taken is to add compound inhibitors during the grafting process.

Example 2

Factors affecting silane grafted cross-linked PE are:

(1) Factors affecting PE silane grafting process

The main process factors affecting PE silane grafting are extrusion temperature and extrusion speed. The speed of the grafting reaction mainly depends on the decomposition speed of the grafting initiator, and the decomposition speed of the grafting initiator strongly depends on the extrusion temperature. As the temperature increased, the half-life of the initiator decreased, and increasing the extrusion temperature was beneficial to increase the rate of grafting reaction. However, if the extrusion temperature is too high, the silane monomer will volatilize, reducing the grafting rate. The temperature of PE silane grafting reaction is generally controlled between 190-210°C. The speed of the extruder determines the residence time of the material in the extruder (reaction time) and the mixing effect. If the residence time is too short, the decomposition of peroxide will be incomplete, and the grafting rate will be reduced. The residual peroxide will directly affect the long-term stability of the grafted material and the formability and appearance of the product. If the residence time is too long, the viscosity of the extruded material will increase and affect the processing performance. Generally speaking, the process requires that the average residence time of PE in the extruder should be controlled at 5-10 times the decomposition half-life of the initiator. The feeding speed not only has a certain influence on the residence time, but also the filling degree of the screw groove is different with different feeding speeds, thus affecting the mixing and shearing effect of the screw on the material. If the feeding is too fast, the extruded material will be discharged unevenly, the surface will be rough and bamboo-shaped, and the process performance will be poor. Feeding is too slow, and the economy is not cost-effective.

(2) Two processes for the preparation of silane grafted cross-linked PE:

One-step method: Originated from M0n0sil technology, it uses a special precision metering system to feed raw materials into a specially designed reaction extruder at one time, and completes the grafting and molding process in one step.

Two-step method: Sioplase technology from Dow Corning. The first step is the mixing and extrusion preparation of silane-grafted PE pellets and catalytic masterbatch. The second step is to extrude the grafted PE pellets and catalytic masterbatch together with PE. The products are heated under hot water or low-pressure steam to cross-link.

Other cross-linking methods will be further described below in conjunction with specific examples.

(1) High energy radiation crosslinking method

The radiation crosslinking method (PE-Xc) is to irradiate the molded product with β-ray or γ-ray to form C-C crosslinking bonds between polyethylene molecules. The resulting product is pure and has superior electrical properties, but the radiation generating device is expensive and the penetration of radiation is limited. It is not suitable for making thick-walled products or products with complex structures. It is mostly used in the production of cable materials, heat-shrinkable tubes and special films.

PE is a typical radiation crosslinkable polymer. How to accelerate radiation crosslinking, suppress side reactions, and reduce the radiation dose to achieve the required gel content (that is, the sensitizing radiation problem of PE) has become the focus of current research.

The general method of PE sensitization to radiation problems is to add sensitizers and sensitizers to PE (some people refer to sensitizers and sensitizers collectively as sensitizers or sensitizers), or to change the irradiation atmosphere (such as in Acetylene, tetrafluoroethylene atmosphere).

Advantages and disadvantages of PE high energy radiation crosslinking method:

Advantages: good processing stability; finished product is pure.

Disadvantages: expensive auxiliary processing equipment; demanding working environment; only suitable for thin-walled products; difficult to complete cross-linking of coils.

(2) Peroxide crosslinking of PE

Peroxide crosslinking has the advantages of strong adaptability and good performance of crosslinked products, so it has been applied in industry.

Peroxide crosslinking differs from radiation crosslinking in that:

The crosslinking process must have a crosslinking agent, that is, the presence of peroxide;

The crosslinking reaction must be carried out at a certain temperature.

When the cross-linking agent is pure peroxide, the reaction process is as follows: peroxide is decomposed by heat to generate free radicals, which attack PE macromolecular chains, capture hydrogen atoms on the molecular chains, and generate PE macromolecular chain free radicals; Macromolecular chain free radicals are highly reactive. When two PE molecular chain free radicals meet, they combine with each other to form chemical bonds between polymer chains and cross-link.

The crosslinking agent used in peroxide crosslinking is organic peroxide, and the commonly used varieties mainly include DCP, BPO and so on. When crosslinking PE with peroxide, the extrusion temperature must be kept very low. Once the extrusion temperature is higher than the decomposition temperature of peroxide, early crosslinking may cause coking, affect the quality of the product or even damage the equipment. The temperature limit The extrusion speed of cross-linkable PE is strictly limited, and when extruding products, there must be a special extruder and high-pressure continuous cross-linking pipeline, which limits the application of this technology in small and medium-sized enterprises.

Advantages and disadvantages of peroxide crosslinking of PE

Advantages: higher degree of cross-linking; better flexibility.

Disadvantages: high requirements for production equipment, high temperature, easy to cause chain breakage of polyethylene molecules, slow production speed and low efficiency.

(3) UV light crosslinking of PE

Ultraviolet light can also cause PE to crosslink. Ultraviolet light crosslinking is transformed into an excited state after the photoinitiator absorbs the energy of ultraviolet light, and then hydrogen abstraction on the PE chain generates free radicals to initiate PE crosslinking.

Breakthrough progress in UV crosslinking of PE

①Using high-power high-pressure mercury lamps instead of low-pressure mercury lamps not only increases the light intensity, but also makes the emission wavelength range suitable for the absorption of the photoinitiator used;

②Cross-linking in a molten state, on the one hand, makes it easy for ultraviolet light to penetrate thick PE samples; Uniformity of joint;

③The high-efficiency initiation system of multifunctional crosslinking agent and photoinitiator is used to complete the crosslinking process in a short time at the initial initiation stage, which not only improves the crosslinking initiation speed, but also increases the crosslinking depth from 0.3mm to 3mm or more.

Advantages of UV crosslinking of PE

Ultraviolet light cross-linking technology has its unique advantages. It is similar to the high-energy electron beam radiation method in terms of technical principle, but it uses low-energy ultraviolet light as the radiation source. The equipment is easy to obtain, the investment cost is low, the operation is simple, and the protection is easy. Therefore, more and more people pay more and more attention to the ultraviolet light cross-linking technology of PE, especially in the development of cross-linked wires and various low-voltage cross-linked cables, which have great market competitiveness and open up a new way for PE cross-linking technology.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention should be included in the protection of the present invention. within range.

Claims (7)

1. A method for polyethylene cross-linking modification is characterized in that, the method for polyethylene cross-linking modification adopts the silane cross-linking method of PE, and silane cross-linking PE takes PE as base resin, and is made of silane as Bridging materials, forming chemical covalent bonds between polymer macromolecular chains to replace the original van der Waals force, so that the molecules form a three-dimensional network; in the preparation of silane crosslinked PE: Grafting stage: The peroxide initiator is decomposed by heat to form primary free radicals, which capture the H atoms on the PE macromolecular chain to form PE macromolecular free radicals, which are combined with vinyltrialkoxysilane CH ₂ =CH _—The vinyl group in Si (OR) ₃ undergoes an addition reaction to form a PE-grafted silane active macromolecule. The active macromolecule realizes chain transfer by capturing the H atom in PE to obtain a PE-grafted silane product, namely grafting Material A; Crosslinking stage: PE grafted silane products are hydrolyzed under the action of organotin catalysts to generate silanols, and silanols are dehydrated or dealcoholized to form PE silane crosslinked products. 2. The method for cross-linking modification of polyethylene as claimed in claim 1, characterized in that, the base resin is a homopolymer and a copolymer of olefins after drying treatment. 3. The method for cross-linking modification of polyethylene as claimed in claim 1, characterized in that, the initiator is DCP, and the consumption of DCP is 0.05-0.5 part. 4. The method for cross-linking modification of polyethylene according to claim 1, characterized in that the cross-linking agent is vinyl unsaturated silane, and the cross-linking agent consumption is 0.5-4 parts. 5. The method for cross-linking modification of polyethylene as claimed in claim 1, wherein the antioxidant is antioxidant 330, 168, 1010, RD and other aromatic amine stabilizers, and complex With antioxidant, the antioxidant content is not more than 1 part. 6 . The method for cross-linking and modifying polyethylene according to claim 1 , wherein the cross-linking catalyst is dibutyltin dilaurate, and the dosage thereof is 0.02-0.15 parts. 7. The method for cross-linking modification of polyethylene as claimed in claim 1, characterized in that, the polymerization inhibitor is added into a composite polymerization inhibitor during the grafting process.