Disclosure of Invention
The invention aims to solve the technical problems of overcoming the defects of the prior art and providing a preparation method of branched nylon, a composite film and a preparation method thereof, wherein lysine is used as a branching agent in the preparation process, and lysine and caprolactam are copolymerized in situ to prepare the branched nylon, so that gel particles or a partial cross-linked structure is not easy to generate, and the subsequent processing is more convenient; and by controlling the dosage of the branching agent lysine, the branched nylon with high viscosity and no gel or crosslinking structure can be synthesized without a solid-phase post-condensation step, the preparation process is simple, and the preparation period is short.
In order to solve the technical problems, the invention adopts the technical scheme that:
a preparation method of branched nylon comprises the steps of putting caprolactam, a branching agent and desalted water into a reactor to react to obtain the branched nylon, wherein the branching agent is lysine.
In the preparation process, lysine is used as a branching agent, and lysine and caprolactam are subjected to in-situ copolymerization to prepare branched nylon, so that gel particles or a partial cross-linked structure is not easy to generate, the probability of difficult melt plasticization in the subsequent extrusion processing process is reduced, and the surface crystal points of the product are few; and because the solid-phase post-condensation step is a solid-solid reaction, the reaction is slow and the conversion rate is relatively low, by controlling the dosage of lysine, the branched nylon can be prepared without the solid-phase post-condensation step.
The method is a method for preparing the branched nylon in an intermittent manner, has simple preparation process and short period, and is suitable for mass production of the branched nylon.
The branching agent is lysine with decomposition temperature higher than 200 ℃. Branched nylon is prepared under high temperature condition of more than 200 ℃, lysine with poor thermal stability at 200 ℃ can not be used as branching agent of branched nylon, because the self decomposition not only makes the prepared branched nylon have poor performance, but also forms impurities to influence the performance of the branched nylon. Therefore, lysine with the decomposition temperature of more than 200 ℃ is used as a branching agent, so that the lysine can be used as the branching agent to react with a caprolactam hydrolysate, and the stability of the branched nylon can be improved.
Putting caprolactam, a branching agent and desalted water into a reactor, and carrying out hydrolytic ring-opening reaction, amidation reaction, chain growth reaction and chain termination reaction to obtain the branched nylon, wherein the weight of the branching agent is 0.01-0.5% of that of the caprolactam. It has been found through experimentation that gel particles or partially cross-linked structures are not easily formed when the weight of lysine as a branching agent is 0.01% to 0.5% of the weight of caprolactam, which makes subsequent processing most convenient. When the weight of lysine as a branching agent is less than 0.01% by weight of caprolactam, the yield of branched nylon is small, and when the weight of lysine as a branching agent is more than 0.5% by weight of caprolactam, the quality of the branched nylon produced is poor.
The preparation method comprises the following steps of adding caprolactam, a branching agent and desalted water into a reactor together to react to obtain the branched nylon.
By adding the molecular weight regulator, the molecular weight of the branched nylon can be controlled, so that the performance of the branched nylon is more controllable.
Preferably, the molecular weight regulator is an organic acid or an organic base.
Preferably, the organic acid comprises one or a combination of terephthalic acid, acetic acid and benzoic acid, and the organic base comprises hexamethylene diamine.
More preferably, the weight of the molecular weight regulator is 0.02-0.5% of the weight of caprolactam, and the desalted water is 2-5% of the weight of caprolactam. The molecular weight of the branched nylon is more controllable by controlling the dosage of the molecular weight regulator.
The catalyst, caprolactam, a branching agent and desalted water are put into a reactor together to react to obtain the branched nylon when the branched nylon is prepared. And by adding the catalyst, the amidation reaction is accelerated, and the production efficiency is improved.
Preferably, the catalyst is ZnO, MgO, SnCl2One or a combination of several of them.
More preferably, the weight of the catalyst is 0.02-0.4% of the weight of caprolactam.
A process for the preparation of branched nylon comprising the steps of:
1) putting caprolactam, a branching agent, a molecular weight regulator, desalted water and a catalyst into a polymerization kettle, uniformly mixing, carrying out hydrolysis ring-opening reaction on the caprolactam under the conditions of high temperature and pressurization, and carrying out amidation reaction on a hydrolysis product of the caprolactam and lysine to form a branched nylon prepolymer;
2) relieving the pressure to normal pressure, heating, and carrying out chain extension reaction on the branched nylon prepolymer to form a branched nylon long chain;
3) maintaining normal pressure, cooling, and carrying out chain termination reaction on the branched nylon long chain and a molecular weight regulator to obtain branched nylon;
preferably, in the step 1), the temperature is increased to 225-240 ℃, and the pressure is maintained for 2-4 hours after the pressure is increased to 2-5 bar;
2) releasing the pressure to normal pressure, heating to 260-275 ℃, and maintaining for 2-5 hours;
3) and maintaining the normal pressure, cooling to 245-255 ℃, and maintaining for 1-4 hours.
The preparation method has the advantages that the temperature is low, the pressure is low, the caprolactam hydrolysis is slow, the reaction between a hydrolysate and a branching agent is slow, the yield is low, the caprolactam hydrolysis speed is high under the conditions of high temperature and pressurization, the branching reaction efficiency between a caprolactam hydrolysate and lysine is high, the preparation time of the branched nylon can be shortened, the temperature is too high, the side reactions of the caprolactam hydrolysate and the lysine are more, the performance of the branched nylon is reduced, and experiments show that the yield of the branched nylon prepolymer is high and the byproducts are less under the conditions of the temperature of 225-240 ℃ and the pressure of 2-5 bar.
The temperature rise is beneficial to the branched nylon prepolymer to carry out chain extension reaction, but the high pressure is not beneficial to the reaction, so that after the amidation reaction of the caprolactam hydrolysate and the branching agent is completed, the temperature is reduced to normal pressure, the temperature is raised, the chain extension reaction is accelerated, but the temperature is too high, side reactions are increased, crosslinking and gelation are easy to occur, and experiments prove that under the normal pressure and at the temperature of 260-275 ℃, the impurities are few, the chain extension reaction speed is high, and the impurities are few.
After the chain growth reaction is finished, the temperature is reduced to balance the chain growth reaction for a period of time, meanwhile, the branched nylon long chain and the molecular weight regulator perform chain termination reaction to obtain branched nylon, the realization finds that the temperature cannot be reduced too much, the temperature is too low, the viscosity of the product can be increased or solidification can occur, and the branched nylon has high viscosity and is not easy to extrude.
The branched nylon obtained by the preparation method has the relative viscosity of 3.00-3.90. The branched nylon prepared by the method has relatively high viscosity, and the branched nylon in the viscosity range has large molecular weight, high branching degree, good melt strength during extrusion processing and slow crystal orientation, has better adaptability with materials of each layer when preparing a composite film, and eliminates the curling phenomenon caused by different shrinkage rates of materials of each layer when preparing the composite film by using common nylon.
A composite film with the branched nylon comprises a branched nylon layer and a polyethylene layer, wherein an adhesive layer is arranged between the branched nylon layer and the polyethylene layer;
preferably, the total thickness of the composite film is 35-55 μm.
The composite film prepared by the branched nylon has the advantages that the relative viscosity of the branched nylon is 3.20-3.90, the crystallinity of the branched nylon is much lower than that of common nylon, good processing performance is brought under the condition of not changing production equipment, the product performance is equivalent to that of a nylon multilayer composite film, but the film is smoother and is not easy to curl.
The composite film comprises two branched nylon layers and a polyethylene layer, wherein the polyethylene layer is sandwiched between the two branched nylon layers, and an adhesive layer is arranged between the branched nylon layer and the polyethylene layer;
or the composite film comprises a branched nylon layer and two polyethylene layers, wherein the branched nylon layer is sandwiched between the two polyethylene layers, and an adhesive layer is arranged between the branched nylon layer and the polyethylene layers;
preferably, the polyethylene is blown film grade low density polyethylene, and the melt index of the polyethylene is 0.3-7 g/10 min;
more preferably, the polyethylene has a melt index of 3g/10 min.
No matter the branched nylon layer/adhesive layer/polyethylene layer/adhesive layer/branched nylon layer or the polyethylene layer/adhesive layer/branched nylon layer/adhesive layer/polyethylene layer, the branched nylon prepared by the method has better adaptability with other layer materials, and the prepared composite film is not curled.
The adhesive layer is made of DuPont's Surlyn' (Surlyn), 1650, which is ternary copolymer made by neutralization reaction of ethylene-methacrylic acid copolymer and metal salt, the copolymer is zinc ion type polymer, and can generate large adhesive force after melting, satisfying the compounding of branched nylon and polyethylene.
The adhesive is matched with polyethylene with a melt index of 0.3-7 g/10min and branched nylon with a relative viscosity of 3.20-3.90, so that the composite effect of the polyethylene and the branched nylon is better, and the prepared composite nylon has good quality and is not curled.
The method for preparing the composite film by adopting the branched nylon comprises the following steps:
1) drying the branched nylon at 100 ℃ for a certain time;
2) respectively putting an adhesive, polyethylene and dried branched nylon into a multilayer co-extrusion film blowing machine, wherein the multilayer co-extrusion film blowing machine is provided with extruders corresponding to the adhesive, the polyethylene and the dried branched nylon respectively, the temperature of a screw of the extruder corresponding to the branched nylon is controlled to be 200-255 ℃, the temperature of a screw of the extruder corresponding to the adhesive layer is controlled to be 180-200 ℃, and the temperature of a screw of the extruder corresponding to the polyethylene layer is controlled to be 190-220 ℃;
3) controlling the temperature of a composite die head of the multilayer co-extrusion film blowing machine to be 210-230 ℃, and carrying out air cooling, blowing, upward traction, slitting, rolling and packaging on a molten material discharged from the composite die head to obtain a finished product;
preferably, the drying time in 1) is 8 hours.
The composite film obtained by the preparation method has good processing performance, the product performance is equivalent to that of a nylon multilayer composite film, and the film is flat and is not easy to curl.
After adopting the technical scheme, compared with the prior art, the invention has the following beneficial effects:
1. in the preparation process, lysine is used as a branching agent, and lysine and caprolactam are subjected to in-situ copolymerization to prepare branched nylon, so that gel particles or a partial cross-linked structure is not easy to generate, and the subsequent processing is more convenient;
2. according to the invention, lysine is used as a branching agent, no vacuum pumping is needed, and polycondensation reaction can be carried out to increase the chain after air is replaced by nitrogen, namely under the condition of nitrogen, so that the reaction condition is mild, the preparation process is simplified, and the energy consumption is reduced;
3. the relative viscosity of the branched nylon is 3.00-3.90, the branched nylon in the viscosity range has the advantages of large molecular weight, high branching degree, good melt strength during extrusion processing, slow crystal orientation, better adaptability to materials of each layer during preparation of the composite film, and elimination of the curling phenomenon caused by different shrinkage rates of the materials of each layer during preparation of the composite film by using common nylon.
The present invention will be described in further detail with reference to examples.
Example 1
A preparation method of a branched nylon resin comprises the following steps:
1) 10000g of caprolactam, 30g of lysine, 20g of terephthalic acid, 300g of desalted water and 10g of SnCl2Putting the mixture into a 30L high-pressure polymerization kettle, introducing high-purity nitrogen to replace air in the kettle, heating to 70 ℃ to melt caprolactam, starting stirring and mixing uniformly, continuously heating to 230 ℃, reacting for 3 hours at a pressure of 2-5bar to hydrolyze and open the ring of caprolactam to generate aminocaproic acid, and carrying out amidation reaction on the aminocaproic acid and lysine to form a branched nylon prepolymer;
2) relieving the pressure to normal pressure, heating to 265 ℃, reacting for 4 hours, and carrying out chain extension reaction on the branched nylon prepolymer to form a branched nylon long chain;
3) maintaining the normal pressure in the kettle, cooling to 250 ℃, reacting for 3 hours, and carrying out chain termination reaction on the branched nylon long chain and terephthalic acid to obtain branched nylon;
4) and after the reaction is finished, pressurizing by using nitrogen to discharge a branched nylon melt, casting and molding, cooling and pelletizing, and extracting and drying to obtain the branched nylon chip.
The relative viscosity of the branched nylon was 3.20.
In a further scheme, the prepared branched nylon is prepared into a composite film, and the preparation method comprises the following steps:
1) firstly, drying the prepared branched nylon for 8 hours at 100 ℃;
2) respectively putting the adhesive, the polyethylene and the dried branched nylon obtained in the step 1) into a multilayer co-extrusion film blowing machine, wherein the multilayer co-extrusion film blowing machine is provided with extruders respectively corresponding to the adhesive, the polyethylene and the dried branched nylon, the temperature of a screw of the extruder corresponding to the branched nylon is controlled to be 200-255 ℃, the temperature of a screw of the extruder corresponding to the adhesive layer is controlled to be 180-200 ℃, and the temperature of a screw of the extruder corresponding to the polyethylene layer is controlled to be 190-220 ℃;
3) and controlling the temperature of a composite die head of the multilayer co-extrusion film blowing machine to be 210-230 ℃, and carrying out air cooling, blowing, upward traction, slitting, rolling and packaging on the molten material discharged from the composite die head to obtain the composite film.
Wherein, the multilayer co-extrusion inflation film manufacturing machine adopts five layers of co-extrusion inflation film manufacturing machines, the structural form of the obtained composite film is a polyethylene layer/an adhesive layer/a branched nylon layer/an adhesive layer/a polyethylene layer (PE/AHV/PA/AHV/PE), the total thickness of the composite film is 35 mu m, and the obtained composite film is flat and is not easy to curl.