is the earliest industrial synthetic resin, has a history of more than 100 years. Because its raw materials are easy to obtain, easy to synthesize and resin curing performance can meet many of the requirements of use, so in the mold plastics, insulation materials, coatings, wood bonding and other aspects are widely used. In recent years, with the improvement of people's safety requirements, phenolic resins with flame retardant, low smoke, low toxicity and other characteristics have attracted renewed attention, especially in airports, railway stations, schools, hospitals and other public building facilities and aircraft interior decoration materials and other applications more and more
Compared with unsaturated polyester resins, phenolic resins have low reaction activity, curing reactions release shrinking water, so that curing must be carried out under high temperature and high pressure conditions, for a long time can only be impregnated with reinforced materials to make pre-immersion (cloth), and then used in the molding process or winding process, severely limiting its application in the field of composite materials. In order to overcome the inherent defects of phenolic resin, further improve the performance of phenolic resin, to meet the needs of high-tech development, people have carried out a lot of research on phenolic resin, improve the toughness of phenolic wax, improve the properties of the phenolic tree, improve the performance of the heat resistance, improve the performance of the process has become the focus of research. In recent years, a series of new phenolic resins have been developed in China, such as boron modified phenolic resin, olefin-based modified phenolic resin, cyanate esterified phenolic resin and open-loop polymerized phenolic resin. Can be used in SMC/BMC, RTM, extrusion, injection, hand paste and other composite molding process. Combined with the author's research work, this paper introduces the progress of the modified research of phenolic resin and the application of the molding process of phenolic composite materials such as RTM and extrusion.
1 Phenolic resin modified research
1.1 polyethylene alcohol reduced phenolic resin
the most widely used in the industry is the use of polyethylene alcohol destaldehyde modified phenolic resin, it can improve the resin to glass fiber bonding force, improve the brittleness of phenolic resin, increase the mechanical strength of composite materials, reduce the curing rate and thus help reduce molding pressure. Phenol formaldehyde resins used as modified phenolic resins are usually synthesized with ammonia or magnesium oxide as catalysts. The polyethylene alcohol acetaldehyde used as a modifier is generally clostaldehyde and acetaldehyde. It is generally dissolved in alcohol when used as a solvent of resin. The resin synthesized by the hydroxymethyl reaction of acetaldehyde and phenolic aldehyde is an excellent special ink carrier resin.
1.2 polyamide modified phenolic resin
polyamide modified phenolic resin improves the impact toughness and bondability of phenolic resin. Polyamide as a modified type is a class of hydroxymerylated polyamide, which uses hydroxymethylene or active hydrogen to react to form chemical bonds during the synthesis of resin or during the process of resin curing. Thin-walled tubes such as fishing rods made of this resin have excellent methic performance.
1.3 Epoxy modified phenolic resin
Composites made from thermosteroid phenolic resin and Bisphenol A epoxy resin mixture can combine the advantages of 2 resins to improve their respective shortcomings, so as to achieve the purpose of change. This mixture has excellent adhesion of epoxy resin, improves the brittleness of phenolic resin, and has excellent heat resistance of phenolic resin, and improves the disadvantage of poor heat resistance of epoxy resin. This modified is through hydroxy-methyl in phenolic resin and oxycodone and epoxy in the chemical reaction, as well as phenolic hydroxyl in phenolic resin and epoxy in epoxy resin chemical reaction, and finally cross-linked into a complex body structure to achieve the goal, is the most widely used phenolic aldehyde toughening method.
1.4 silicone modified phenolic resin
silicone resin has excellent heat and moisture resistance. The heat and water resistance of phenolic resins can be improved by using silicone monosomes to react with phenolic hydroxyl or hydroxymedehyde in linear phenolic resins. The modified phenolic resin with different properties can be modified by different silicone monosomes or their mixed monosyls and phenolic resins, and has a wide range of selectivity. Composite materials prepared with silicone modified phenolic resins can be used for a considerable period of time at 200-260 degrees C and can be used as instantaneous high temperature resistance materials for ablation materials such as rockets and missiles.
1.5 Boron-modified phenolic resin
Because of the introduction of inororate boron elements into the molecular structure of phenolic resin, boron-modified phenolic resin heat resistance, instantaneous high temperature resistance, ablation resistance and force performance is much better than ordinary phenolic resin. They are mostly used in space technology fields such as rockets, missiles and space vehicles as excellent ablation-resistant materials.
most common is the use of boric acid and phenol reaction, the production of phenyl borate, and polyformaldehyde or formaldehyde aqueous solution reaction, the production of a boron-containing phenolic resin. Boricol resin curing at 900 degrees C residual carbon rate of 70%, decomposition peak temperature of up to 625 degrees C. In addition, the flexible -B-O-key, toughness and resynant properties have been improved in the molecular structure of boricol aldehyde, and the three-way crosslinking structure containing boron in curing products has been introduced, which makes it better resistant to ablation and neutron radiation than to general phenolic resins. The curved strength of the carbon cloth boron phenol laminate is 420 MPa, the shear strength is as high as 39.7 MPa, and the oxygen-acetylene mass ablation rate is only 0.0364 g/s, which is 20% lower than the carbon/phenolic material. The water resistance of bisphenol A boron aldehyde resin, which is synthesized by formaldehyde aqueous solution, has been further improved. In the 1970s, Beijing Bosteel Composites Co., Ltd. (Beijing 251 Factory) and Hebei University successfully developed boricol resin, but only in recent years, the real mass production, the current annual output of about 20t.
1.6 rubber modified phenolic resin
is an effective method of toughening by mixing butyl rubber into phenolic resin. Rubber addition is usually 2% to 10% of the resin quality, impact toughness can be improved by more than 100%. Due to the poor solubility of the two, it is available to synthesize the reaction rubber modified phenolic resin by using end-phenyl or end-amine-based butyl rubber and phenolic hydroxymethyl reaction. The resin can be widely used in aerospace and other fields.
1.7 ethylene-based or acrylic-based modified phenolic resin
generally with line-type phenolic aldehyde as the parent, in the phenolic oxygen level or benzene ring on the introduction of acetylene, acetylene, propylene and so on. Its curing is mainly achieved through the polymerization of different function groups, changing the traditional phenolic coagulation curing method. The polymerization of acetylene and propylene is relatively easy, while benzene acetylene requires a higher curing temperature. These polymers have a lower molecular mass, except for the enlargement chain of the part of the propylphenol resin and the higher molecular mass. These polymerized phenolic resins have better thermal stability and higher residual carbon rates than conventional thermosolytic resins.
the Institute of Chemistry of the Chinese Academy of Sciences carried out a synthetic study of propyl phenolic resins, prepared by the resin has a good process, 100 degrees C viscosity of no more than 400 mpa.s; C for thermoclytic curing, thermal curing material heat resistance than traditional phenolic resin has significantly improved, DMA shows that the resin curing has a glassy temperature of up to 370 degrees C, TGA indicates that its initial thermal decomposition temperature is above 400 degrees C.
can be used to copolymerize a high temperature resin for RTM molding using bimarylamide and acrylic-based line phenolic resins (BMAN). The viscosity of the resin <150 mpa.s within 100 degrees C/8 h is suitable for RTM molding and molding processes. And the resin has good high temperature resistance, DMA analysis shows that the resin casting body die curve inflection point temperature Tonset is above 390 degrees C, glassing temperature >400 degrees C. Quartz fiber/BMAN resin composites also have good high temperature resistance and can be used at 350 degrees C.
1.8 phenolic cyanate resin
phenol cyanate generally refers to the line-type phenolic resin as the skeleton, phenolic hydroxyl by cyanate can be replaced by the formation of phenolic resin derivatives, in the heat and catalyst action of the tricyclic reaction, the formation of a high cross-density network structure containing triennium ring large molecules. Its curing reaction is self-curing system, which produces non-volatile small molecules and has low shrinkage. The resin combines the processing process performance of butyl epoxy resin, the high temperature performance of bi-Malayamide and the flame retardant properties of phenolic resin. At the same time, the resin also has excellent dielectic properties, is the preparation of high-speed digital and high-frequency printed circuit boards and high-power motor insulation accessories excellent materials, but also the manufacturer of high-performance transmission structure materials and aerospace high-performance structural composite materials ideal substrate materials.
Beijing Institute of Glass and Steel Research and Design, in cooperation with Northwestern University of Technology and other units, using the improved phenol-brominated cyanide monomean resin, and infrared, gel experiments and thermal weight loss analysis (TGA) to characterize its structure and performance. Compared with the traditional phenol-brominated cyanide method, the improved phenol-brominated cyanide method obtained a stable performance synthesis product, the product at 200 degrees C gel time of 6.5min, no smoke in the gel, blackening phenomenon, curing resin at 800 degrees C nitrogen atmosphere residual carbon rate of 63.6%. 637, East China University of Technology and other units have also carried out this type of resin research work.
1.9 benzodiazine resin
A class of intermediate benzodias containing hemline structure is synthesized from phenolic compounds, amine compounds and formaldehyde. Under the action of heating and/or catalyst, an open-loop polymerization of benzodiazepines can occur to produce a mesh structure containing nitrogen and similar to phenolic resins. We usually refer to this new resin as an open-loop polymerized phenolic resin. This benzodialyc resin is not released by small molecules during molding and curing. No low molecular release in the process of open-loop polymerization improved the molding processing of phenolic resin, and the product pore rate was low and the performance was greatly improved.
Since 1990, Sichuan University has carried out systematic and extensive research on the synthesis, performance, open-loop reaction system, reaction dynamics, volume change in curing process, computer molecular simulation, composite material preparation, performance research and application.
1.10 Xylene modified phenolic resin
xylene modified phenolic resin is the introduction of hydrophobic structure in the molecular structure of phenolic resin xylene ring, thus the modified phenolic resin water resistance, alkaline resistance, heat resistance and electrical insulation performance has been improved.
1.11 Diphenyl ether formaldehyde resin
dephenyl ether formaldehyde resin is the use of diphenyl ether instead of phenol and formaldehyde shrink, diphenyl ether formaldehyde resin glass fiber-reinforced composite materials have excellent heat resistance, can be used as H-grade insulation materials, it also has good radiation resistance, moisture absorption is also very low.
1.12 Bimaride modified phenolic resin
in the phenolic resin introduced excellent heat resistance of bimalylamide, because of the hydrogen ion shifting and addition reaction between the two, so some phenolic hydroxyl has isolation or blocking effect, so that the thermal decomposition temperature of modified resin significantly increased, for improving the resistance of the resistance material high temperature performance has a great effect.
bimalimide modified phenolic resin has outstanding heat resistance, thermal deformation temperature (HDT) of 273 degrees C, glass temperature (Tg) for production and use growth is very rapid. The main reason why phenolic glass steel can be widely used abroad is that the products have their unique advantages in terms of performance, and second, the production and research and development of phenolic glass steel is more mature, involving almost all kinds of process methods. In contrast, China in the production and application of phenolic glass steel, there is a big gap with foreign countries, the production of molding methods are not many, limited to molding, cloth band winding, and the recent development of hand paste technology. RTM, extrusion and other phenolic glass and steel molding process, has just started, but showed a strong momentum of development.
2.1 RTM molding process (Resin Transfer Molding)
The basic principle of RTM molding process is to lay fiberglass or other reinforced materials in a closed mold cavity, using pressure (or vacuum assist) to inject resin adhesive into the mold cavity, soak through the reinforcing material, and then cure, release molded products. The RTM molding process is a new composite molding process that evolved from the wet paving and injection molding process. RTM process usually uses reinforced materials in the form of short-cut fiber felt, continuous fiber felt, three-dimensional fabric or special composite felt, the types of reinforced materials are glass fiber, aramid fiber, carbon fiber and so on. RtM molding process using unsaturated polyester resin as the substrate has been widely used, and systematic in-depth research has been carried out on resin system, reinforced material coating, fluidized properties, mold design and manufacture, product structure design, special equipment, etc.
and phenolic resins are used in RTM processes in China only in recent years. The RTM production process usually requires a viscosity of approximately 250-500 mpa.s at the injection temperature of the resin to allow the fibers to penetrate quickly and avoid damage to the coating or fabric structure. The resin curing process should not or minimize the production of small molecules to reduce product defects and improve various properties. Traditional phenolic resins are not suitable for RTM process molding because they are cured by compaction and curing process with small molecules released, which can easily cause product defects.
current domestic demand for phenolic and other high-performance resin RTM molding process mainly from military products. However, due to the lack of special RTM phenolic resin, can only use traditional phenolic resin injection, curing is still using pressurized method, has developed many products, and achieved better results. RTM has become one of the most important molding processes for advanced composite materials in aerospace. Sanjiang Group's Yan Pingjiang and others, using RTM molding process method, using acetaminophen resin composite high-strength fiberglass three-dimensional braids, respectively, produced tensile strength test film, bending strength test film, oxyacetylene ablation test film, test film fiber volume content of 55%. Performance test results are: stretch strength of 744MPa, stretching module of 40.6GPa, fracture strain of 2.07%, bending strength of 456.4MPa, bending module of 31.8GPa, its mechanical properties close to steel, ablation performance is much better than molding and winding composite materials. Feng Zhihai and others have also made in-depth research in this regard, and applied to product production. In addition to the traditional acetaminophen, the high carbon phenolic resin developed by East China University of Technology is also a modified acetaminophen resin developed for the RTM process, which has a high carbon content and a wide process operating platform. However, the traditional compaction curing method is still used, with small molecules released and pressurized molding is required.
to meet the needs of special uses, the development of RTM-specific modified phenolic resin has become a hot research topic. The study of acrylic-based modified phenols and biama copolymer resins, cyanate modified phenols (phenols) developed by Beijing Glass Steel Institute, and the opening ring of research conducted by Sichuan University