Surface Treatment Of UHMWPE Fiber

The surface treatment of UHMWPE fiber can be divided into physical modification and chemical modification according to different principles of treatment methods. According to the different modified media used, many methods can be subdivided. When studying the modification effect, it should be noted that a method often has both physical modification and chemical modification characteristics. Therefore, in the following discussion, according to the specific processing media are classified.
Plasma treatment
Plasma treatment is divided into two types: low temperature plasma treatment and plasma graft surface treatment.
The so-called HMWPE fiber low-temperature plasma surface treatment is to vacuum the cleaned HMWPE fiber between the two plates of the plasma treatment device, start the plasma generating device under the environment of less than 40Pa, perform low-temperature plasma treatment on the fiber for a certain period of time, and then remove the fiber for storage.
The so-called UHMWPE fiber plasma graft surface treatment is to immerse the cleaned UHMWPE fiber in monomer solution, take it out after a certain period of time, and place it in a low-temperature plasma device for further treatment. After treatment, active points are generated on the fiber surface to trigger the graft polymerization of monomer on the fiber surface. Finally, the homopolymer on the fiber surface was washed with acetone and stored for later use.
The weak binding layer (WBL) formed on the surface of UHMWPE fiber in the spinning process is further crosslinked by the ultraviolet radiation of plasma, and the cohesion strength of UHMWPE fiber surface is improved. In addition, a variety of active groups can be formed on the surface of the fiber after plasma treatment, such as: -C-O H -, -co -, -COOh, -COO - and other active groups, which are conducive to the chemical combination of the fiber and the matrix resin. Plasma treatment also produces grooves on the fiber surface and increases the surface roughness, which is conducive to mechanical bonding with the matrix. The performance of HMWPE fiber as a composite material is greatly improved by this method, and the interlayer shear strength is increased by more than 3 times. However, the attenuation rate of the active groups of UHMWPE fiber after plasma surface treatment is relatively large, and the attenuation rate is one third in two hours. And the treatment method requires a high vacuum, requiring pressure less than 40Pa. Therefore, UHMWPE fiber plasma surface treatment is difficult to achieve continuous chemical industrial production.
Corona discharge treatment
The so-called UHMWPE fiber corona discharge surface treatment is to place the cleaned UHMWPE fiber between the two plates of the corona treatment device under normal pressure to load about 60 KV high voltage, the power is about 350W, so that the air is ionized, corona is generated, and the treatment is taken out for use after a certain time.
Corona discharge surface treatment can etch the surface of UHMWPE fiber, increase the contact area between fiber and resin, and form mechanical meshing action after resin curing on fiber surface. The size of mechanical meshing is closely related to the degree of infiltration of resin on fiber and the contact area between resin and fiber, but the maximum strength of this physical action is only 24 K J · mol-1. Therefore, it is limited to improve the interfacial bonding strength of fiber and resin by corona discharge alone. Only corona discharge treatment has been reported for industrial treatment of polyolefin films. Although some industrial products of HMWPE fiber are currently treated by simple corona discharge, the effect is not very obvious. And corona discharge treatment is largely limited by intermittent operation. Therefore, it is very difficult to realize industrialization and continuity of corona discharge treatment.
Irradiation induced surface grafting
The so-called UHMWPE fiber irradiation induced surface grafting treatment is to graft polymerize the second monomer on the surface of the fiber by radiation, and produce a buffer layer that can be closely bonded with the matrix, so as to improve the adhesion between the fiber and the matrix. Usually the radiation source is 60C, gamma ray/ultraviolet light, etc., in which ultraviolet light initiates the photosensitizer, such as benzophenone (BP), and then the photosensitizer initiates the monomer grafting to the surface of UHMWPE fiber. At present, the second monomer used is propylene monomer, such as: acrylic acid (AA), acrylamide (AM), glycidyl methacrylate (GMA) and so on.
UHMWPE fiber UV-triggered crosslinking surface treatment can realize continuous process in theory, and only affects the thin surface layer, so it has the prospect of industrial application. However, because the fiber needs to be irradiated for a certain period of time, intermittent operation limits its application to a large extent.
Oxidation process
The so-called UHMWPE fiber oxidizing surface treatment method is to oxidize the fiber surface by chemical agents or gases, so as to change the roughness of the fiber surface and the content of polar groups on the surface. According to the oxidation medium can be divided into wet method and dry method two categories. Wet method is liquid phase oxidation, its common media are: K2 Cr2O2 + H2 SO4, KMnO4+ HNO3, H2O2 (30%) and so on; The clean UH2MWPE fiber is immersed in the medium, taken out after oxidation treatment at the specified temperature for the specified time, and washed to neutral; Wash in deionized water several times, dry and set aside. Dry method is gas phase oxidation method, commonly used photooxidation and ozone oxidation; After pretreatment, the clean UHMWPE fiber is exposed to medium gas, taken out for a certain reaction time, cleaned with ionized water, dried for use.
The liquid oxidation method is relatively mild and easy to control, but the operation is cumbersome, the equipment requirements are high, and the pollution is serious. In the process of gas phase oxidation, the equipment is simple, the operation is convenient, and the continuous production is easy, but the oxidation degree is difficult to control, which may cause the oxidation degree to be too deep and cause the fiber strength to decline. In short, to achieve continuous oxidation surface treatment, it is necessary to make certain improvements in operating methods and equipment.
Chemical crosslinking treatment
Chemical crosslinking method is the direct use of initiator to initiate monomer grafting on the fiber surface, similar to irradiation initiated grafting method, but can avoid irradiation grafting method in equipment investment, this method is simple process, easy to achieve industrial continuous production.
Lang Yanqing et al. used peroxide as initiator to perform silane crosslinking modification on UHMWPE fiber. The study found that after silane modification, silane molecules were grafted on the fiber surface, which increased the number and polarity of chemical functional groups on the fiber surface, thus improving the bonding property between the fiber and the matrix resin. After graft treatment, more markings appeared on the surface of the fiber, which increased the mechanical interlocking effect between the fiber and the resin, and increased the interlayer shear strength of the composite, which was 2.45 times that of the composite before modification. At the same time, the creep resistance of modified fiber is also improved.
Other processing methods
In addition to plasma treatment, chemical reagent oxidation, surface grafting and corona discharge treatment, calendering and coating methods can improve the bonding properties of UHMWPE fiber and resin matrix to a certain extent.
The calendering method is that the UHMWPE fiber is changed from the original circular section to a flat shape after the action of a pair of press rollers, so that the contact area is increased in the composite, and the bonding property is improved to a certain extent, but it is not obvious. The coating method is to coat a layer of reagent on the surface of UHMWPE fiber. From the industrial production of ultra-high molecular weight polyethylene fiber so far, the ideal reagent has not been developed for coating. This reagent should act as a coupling agent to improve the bonding property between UHMWPE fiber and matrix. The effect of these methods on improving the interlayer adhesion between UHMWPE fiber and matrix is not obvious, so the modification research of these methods is not as much as the previous methods.
Due to the current methods, while improving the fiber wettability, the mechanical properties of the treated fibers will be reduced to varying degrees, and the application of the fibers will be limited. Some people put forward a composite treatment method to treat UHMWPE fiber, which can solve this problem. Wang Chengzhong et al. carried out compound surface treatment of UHMWPE fiber by chromic acid liquid phase oxidation and nano silica sol coating, and studied the interface properties of UHMWPE fiber/epoxy resin composite. The results show that both liquid phase oxidation and surface coating can improve the interface properties of the composite materials, but the liquid phase oxidation treatment time is too long, the fiber strength will be reduced, while the composite treatment has a synergistic effect, can not reduce the fiber strength but greatly improve the interlayer shear strength of the composite materials, is an effective surface treatment method.