PET maintains excellent physical and mechanical properties over a wide temperature range. Its excellent fatigue, abrasion and aging resistance, outstanding electrical insulation, stability to most organic solvents and mineral acids, and its production It has been widely used in plastic packaging bottles, films and synthetic fibers due to its low energy consumption and good processability PET can be used in the following fields as its engineering plastics, with consumption of 26% for electrical appliances, 22% for automobiles, , Machinery 19%, appliances 10%, consumer goods 10%, the other 13% .Because PET is widely used in automotive, electrical and other industries, and these industries have strict requirements on material combustion and safety performance, therefore, to improve the flame retardant properties of PET Plastic one of the most basic requirements.No matter as a plastic or fiber, the flame retardant properties of the material are higher, so the development of flame-retardant PET is increasingly becoming an important area of PET materials research.Preparation of flame-retardant PET materials are as follows Three kinds:
A flame retardant PET flame retardant method
Addition of flame retardants in the PET matrix by adding a suitable type and amount of small molecular compound flame retardant, the use of flame retardant and the matrix material in the combustion of the gas phase or (and) the role of flame retardant aggregation to improve the resistance of PET It has the advantages of simple method, low cost, convenient and flexible adjustment of the flame retardancy and flame retardant level of the obtained PET to meet the needs of various practical applications, and is thus a widely used method. The main problem is that most of these small molecule flame retardants have low flame retardant efficiency and large amount of addition, giving PET flame retardancy at the same time they often have a negative impact on the processing and mechanical properties of the material.In addition, these flame retardant The chemical composition of the agent is quite different from that of the PET. Therefore, the compatibility of the agent is poor. During the processing and use, the flame retardant may migrate and precipitate from the PET, affecting the appearance quality of the product and the persistence of the flame retardant effect.
Figure 1 high temperature self-crosslinking copolyester flame retardant anti-drop diagram
There are many kinds of compounds that can be added as flame retardants into PET, such as adding DBDPO to PET can play a good flame retardant effect, because the flame retardant contains high content of bromine, decomposition temperature Above 350 ℃, it is a kind of brominated aromatic flame retardant with high purity and excellent thermal stability.But since the 1980s, it has been found that the pyrolysis products of DBDPO contain polybrominated dibenzodioxane PBDD) and polybrominated dibenzofurans (PBDF), of which the latter has a strong carcinogenic effect, the risk assessment on this issue is still under study and many countries have not taken any measures to limit the current domestic resistance Burning PET plant is still widely used as the main flame retardant DBDPO.
Flame retardant PET is added to PET by adding triphenyl phosphate, tricresyl phosphate, triethyl phosphate, brominated triphosphate (TDBPPE), etc. Flame retardant is also adopted by adding flame retardant, wherein TDBPPE is particularly suitable PET flame retardant, which is because TDBPPE contains bromine and phosphorus in the same molecule, with halogen-phosphorus synergistic effect, and phosphorus flame retardant efficiency in PET extremely high. TDBPPE flame retardant PET, with the three oxide Antimony and can also be used alone.With TDBPPE flame retardant 30% glass fiber reinforced PET, sodium antimonate and TDBPPE confrontation between, can significantly reduce the oxygen index and flame retardant materials, for example, with 15% TDBPPE and 5% sodium antimonate flame retardant 30% glass fiber reinforced PET, the material oxygen index was 29.4%, UL flame retardant grade V-2 level (1.6mm), burning time is 5.1s. But if the 5% TDBPPE replaces 5% sodium antimonate in the original formulation, the oxygen index of the material is increased to 36.5%, the flame retardancy is V-0, and the burning time is reduced to 0.1s. For the oxygen index of PET flame-retardant material, TDBPPE the effect is better.But as a phosphate additive type flame retardants are also inadequate, mostly phosphate flame retardant Liquid, poor heat resistance, high volatility, compatibility is not good enough, and the flame retardant phosphorus content is generally proportional to the flame retardant effect.Therefore, the development has excellent heat resistance and compatibility, easy to use and other advantages of solid High molecular weight polycondensation phosphate as a phosphorus flame retardant is the development trend of the United States Monsanto developed Phosgard 2XC-20 is a non-volatile phosphate flame retardant, which is used for PET flame retardant achieved better Effect.
Figure 2 High temperature self-crosslinking copolyester functional monomer
Inorganic phosphorus flame retardants can also be used for flame retardant PET materials, mainly red phosphorus, phosphate, ammonium polyphosphate, a non-halogen flame retardants, of which red phosphorus is a better PET flame retardant, with added Less amount, wide use, etc. Since red phosphorus only contains flame retardant elements, it is more efficient than other phosphorus flame retardants, especially for PET oxygen containing polymer materials, but ordinary red phosphorus absorbs moisture easily and emits Phosphine gas, and poor compatibility with PET, it is generally difficult to directly use as a flame retardant and microencapsulated red phosphorus flame retardants reduce the activity of red phosphorus, to solve the compatibility problems, so that the red phosphorus In the practical application plays an important role in the recycled PET plastic by adding 5% by mass of microcapsule red phosphorus, synergistic addition with the inorganic flame retardant, the results of limit oxygen index (LOI) reached 35.5 with the red phosphorus Development of flame retardants, the development of whiteness of the microcapsule red phosphorus flame retardant to overcome the red color of the flame retardant in the material used in the color limits, due to its compatibility with the resin is good, not reddish during use , High flame retardant efficiency, toxicity and other advantages, it is more suitable for natural flame retardant PET workers Plastic .In addition, phosphate is also an effective flame retardant in thermoplastic polyester.Among them, ammonium polyphosphate (APP) is a phosphorus-based inorganic flame retardant developed in recent years because of its high phosphorus content, nitrogen It has many advantages such as good thermal stability, low water solubility, high flame retardance and so on, so it has been widely used in many fields.However, due to the thermal decomposition of small molecular compounds at high temperature, it is difficult to meet the requirements of thermoplasticity at higher temperature Therefore, in recent years, the microcapsule technology has been used to coat the APP to give it higher thermal stability and water resistance as a flame retardant for PET engineering plastics.
Nitrogen-based flame retardants can also be used for flame-retardant PET, the current application of nitrogen-containing flame retardants mainly include three categories: melamine, dicyandiamide, guanidine salts and derivatives, including melamine, melamine cyanurate and melamine phosphate Is the flame retardant market has the most potential varieties.Nitrogen flame retardants on the flame retardant mechanism, nitrogen flame retardants are generally considered thermal decomposition, easy to release ammonia, nitrogen, deep nitrogen oxides, water vapor, etc. Non-flammable gases, the formation of non-flammable gases, and the decomposition of endothermic flame retardants (including the partial sublimation of flame retardants) take away most of the heat and greatly reduce the surface temperature of the polymer. Non-flammable gases play a role in diluting the air Of oxygen and PET pyrolytic gas generated by the role of flammable gases, and because PET has the presence of nitrogen flame retardants, but also with the combustion of oxygen in the air reaction of carbon dioxide, water and nitrogen oxides, oxygen in the surface of the consumption of materials Of the same time, to achieve a good flame retardant effect of nitrogen flame retardant is the main advantage of efficient flame retardant, non-halogen, non-corrosive effects.
Second, PET copolymer flame retardant
Copolymerization of fire-retardant PET is a reactive flame retardant as a third monomer involved in the PET polymerization reaction prepared PET flame-retardant composite materials. Reactive flame retardants generally contain P, N and other flame-retardant elements, the presence of these elements Can improve the flame retardancy of the polymer by changing the thermal degradation process of the polymer matrix, etc. In the PET synthesis of terephthalic acid and ethylene glycol, adding the reaction system which can participate in the reaction and has the flame retardant property Three monomers (the use of the third monomer mainly containing phosphorus diol or triol), so that it is involved in the synthesis of PET reaction to make it bonded to the molecular chain and thus play a flame retardant effect, but has obtained industrial The application of such flame retardant rarely, mainly due to its low phosphorus content, poor stability, easy to aggregate when synthesized.
Figure 3 Schematic diagram of the vertical combustion process with diphenyl acetylene structure copolyester
Copolymerization method to obtain a flame retardant PET is also known as structural flame retardant PET obtained flame retardant PET copolymerization flame retardant monomer is also phenyl dicarboxy phenyl phosphine oxide (BCPPO), which is A very typical copolymerization flame retardant monomer, not only has excellent flame retardant properties, but also can improve the performance of many flame retardant PET. BCPPO is an organic phosphine oxide, high thermal stability, the thermal decomposition temperature of 350 ℃, the temperature corresponding to the maximum decomposition rate is above 450 ℃, and the amount of decomposition residue is up to 40% at 650 ℃, so the copolymerization of BCPPO as PET copolymerized flame retardant monomer at polymerization temperature Will break down.In addition, BCPPO contains bifunctional groups, with ethylene glycol and terephthalic acid copolymerization copolymerization flame retardant PET due to organophosphorus flame retardant elements randomly copolymerized in the macromolecular chain, resulting flame retardant PET has a permanent Of the flame-retardant properties of copolymerization of flame-retardant material is called the nature of fire-retardant materials, due to the special chemical structure, even without adding flame retardant also has sufficient flame retardant properties of the inherent flame retardant polymer with high thermal stability, Low burning speed as well Good ability to prevent the spread of fire, even when the face of a very high heat flow as well.
Some scientists synthesized '(6-oxo-6-dibenzo- (c, e) (1,2) -oxaphosphorin-6-one) Is a new copolymer of PET flame retardant third monomer.DDP molecular structure of the biphenyl phosphate and the formation of a stable ring structure, and in the side chain position has good thermal stability and hydrolysis resistance, it and PET Copolymerization can improve the flame retardancy of PET, overcome the shortcomings of easy hydrolysis of flame-retardant PET, and maintain the original PET processing performance, has broad application prospects. 2-carboxyethylphenyl hypophosphorous acid (CEPPA) is also PET synthesis When the flame retardant third monomer, CEPPA belongs to the hypophosphorous acid derivatives, strong acid, the compound hydroxyl and carboxyl with higher reactivity because CEPPA contains phosphorus, and has high thermal stability and oxidation Stability, it is an excellent PET reactive flame retardant.It was used CEPPA as the third monomer, and in situ added phosphate glass (P-glass) Synergy, in-situ copolymerization in the P-glass content Different PET / P-glass flame retardant materials, the experimental results show that the addition of P-glass can promote the system charcoal, at the same time, with the amount of P-glass added The flame retardancy and droplet resistance of the composites were improved.When the content of P-glass reached above 1%, the LOI reached over 30% and the UL94 vertical burning level reached V-0.In addition, The study of non-isothermal crystallization behavior found that P-glass had little effect on the crystal structure of PET, but decreased the crystallization rate of PET.
Fig.4 Schematic diagram of flame-retardant anti-droplet of ionomer (a) and ionomer after oxygen ion index test (b)
In addition, bisphenol A and bisphenol F, 10-hydroxy-10-oxo-10 hydrogen-phenanthrene-2,8-dicarboxylic acid potassium salt (DHPPO-K) Some people, respectively, as a third monomer bisphenol A and bisphenol F involved in the polymerization of PET to prepare two kinds of PET. The thermal stability of both PET relative to pure PET have a certain increase, but the flame retardant Performance is not greatly improved. The LOI of bisphenol A-type PET is only increased from 22% to 25%, UL-94 grade is best to V-2 grade, and the droplet is serious; while bisphenol F-type PET is slightly better, LOI Up to 26%, and can produce unstable charcoal layer, have a certain inhibitory effect.Here researchers with DHPPO-K as the third monomer and terephthalic acid, ethylene glycol copolymerization, obtained with ions (PETIs-K) with similar phosphorus-containing heterocyclic PET (PETPs) as control.It is found by experiments that PETIs-K has higher thermal stability, DHPPO-K can promote the substrate The formation of a stable carbon layer at high temperatures degrades the flame retardance of the material.Although PETPs and PETIs-K have higher LOIs, PETIs-K also has higher self And anti-droplet properties.PFPs and PETIs-K in the flame retardant materials in different ways, PETPs in the degradation of phosphorus materials into the gas phase, and phosphorus in PETIs-K mainly in the cohesion phase .
Third, PET smart flame retardant method
Smart flame retardant PET recently proposed by the scientists, intelligent flame-retardant PET in the molding process is not different from ordinary PET, but when the PET is ignited its chemical structure will change, such as the occurrence of rapid cross-linking applications, so that the melting Body viscosity rapidly increased and accelerated carbonization, which play a dual role of flame retardant and anti-droplet, shown in Figure 1. Typical PET smart flame retardant is melt-polycondensation in PET molecular chain into the self-crosslinking functional groups (Such as stilbene, azobenzene, phenylmaleimide, etc.), as shown in Figure 2 Preparation of self-crosslinking copolyesters obtained copolyester can maintain the original characteristics of PET case, the resistance No melting droplets, as shown in Figure 3. At the same time, this copolymerization PET does not contain any traditional flame retardant elements (such as Cl, Br, P, etc.), which provides a completely new method for green flame retardant new technology.
For smart flame-retardant PET, two other types of smart flame-retarding technologies have recently been proposed by scientists, that is, 'ionic polymer drop resistant' and 'high temperature self-weight resistive droplet.' Chemical crosslinking with high temperature self-crosslinking In contrast, ionic polymers are reversibly physically cross-linked to increase the melt viscosity of the material to achieve droplet resistance (Figure 4). Scientists recently designed a series of phosphorus-containing flame retardant monomers, the resulting ionomer poly Esters showed better flame-retardant anti-drop effect. 'High-temperature self-weight anti-droplet' is introduced into the PET molecular chain can be high temperature rearrangement of the structure at high temperatures by polymer rearrangement of molecules to promote the material Into carbonization, to achieve flame retardant droplet.
Fourth, conclusion
At present, the industrial preparation of PET flame retardant materials is still based on the addition of flame retardants, mainly due to flame retardant modified PET material does not change the PET polymerization process, the method changes flexible and easy to adjust. Add flame retardant Preparation of PET flame retardant material has many advantages, through the synergistic effect of a variety of flame retardants can effectively improve the flame retardancy of the composite material, but the added flame retardant generally poor compatibility with PET, the amount is usually higher , Will cause the appearance of the product, the mechanical properties of the decline.How to design flame retardant compound formulations, as well as to overcome the compatibility and dispersion caused by blending flame retardant modification and other issues, without serious impact on other properties Case, to bring good flame retardant properties for the material is the current research focus, but also the future of the main development direction of PET flame retardant materials. Copolymerization flame retardant modification method is more mature, but it has limitations, as the third monomer Reactive flame retardant PET materials need to change the process of PET polymerization production, the face of a large number of PET products, this flame-retardant method is less common, higher cost.Developed a new copolymerization flame retardant PET, Its high universality, is an important development direction of current PET copolymer modified flame composite. PET study of intelligent fire retardant is just emerging, but it has unlimited potential for development.