Crosslinkable thermoplastic polyurethane and preparation method thereof

Abstract

According to the cross-linkable thermoplastic polyurethane and the preparation method thereof, a maleic anhydride modified chain extender is prepared through esterification reaction of maleic anhydride and butanediol, reversible cross-linking bonds are formed, the thermal deformation resistance stability of the material is improved, and the material is suitable for extrusion application mainly including automobile cables, cables, pipes and sealing elements. The thermoplastic polyurethane material is excellent in heat resistance, and can meet the performance indexes of C-type cables in ISO (International Standard Organization)-6722 cables.

Description

Technical Field

[0001] The present invention relates to the technical field of polyurethane materials, and particularly relates to a crosslinkable thermoplastic polyurethane and a preparation method thereof. Background Art

[0002] Thermoplastic polyurethane is a thermoplastic polymer with repeating -NHCOO- structural units in the main chain. It has excellent wear resistance, resistance to media, and environmental resistance, and can be prepared in various colors to meet appearance requirements. Since its molecular structure can be adjusted to meet different application needs, it has been widely used in various industries in recent years. In many applications, having good chemical resistance, dimensional stability, heat resistance, and oxidation resistance is crucial for the application of TPU. For example, for seals, gaskets, wires, and cables used in industrial applications, these excellent chemical and physical properties are crucial. Especially in the application of automotive parts, parts made of TPU may be exposed to high temperatures and organic liquids such as gasoline and engine oil. Spark plug wires and other wires used in automotive applications need to be oil-resistant and heat-resistant at the same time. Seals and gaskets used in internal combustion engines, heavy equipment, appliances, and countless other applications also need to be heat-resistant and solvent-resistant. Therefore, improving the heat resistance and solvent resistance of TPU materials has become one of the key research directions for researchers.

[0003] Patent CN102803331 B discloses a preparation method of a crosslinkable thermoplastic polyurethane. The composition of the material is as follows: (1) a saturated hydroxyl-terminated intermediate, (2) an unsaturated hydroxyl-terminated intermediate, where the unsaturated hydroxyl-terminated intermediate contains carbon-carbon double bonds, (3) a polyisocyanate, and (4) a saturated diol chain extender. After processing, the material forms a crosslinked structure by electron irradiation to improve its heat distortion performance. However, its preparation process requires two steps to achieve the crosslinking effect, with a cumbersome process and certain limitations. Patent CN106795264 A discloses a preparation method of a high heat-resistant thermoplastic polyurethane, which involves a new thermoplastic polyurethane containing an alkylene-substituted spiro compound as a chain extender and a polycarbonate polyol. The TPU material prepared by this invention has good heat resistance, but its crosslinking is irreversible, and it is easy to produce more thermosetting materials, resulting in material waste and pollution. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a thermoplastic polyurethane with high heat resistance stability and a preparation method thereof. The present invention improves the problem of poor heat resistance stability of TPU, reduces the process steps and equipment requirements at the same time, improves production efficiency, greatly optimizes the use temperature range of such materials, and the material can be recycled and processed without causing excessive material pollution.

[0005] To achieve the above-mentioned invention object, the present invention provides the following technical solutions:

[0006] The present invention provides a crosslinkable thermoplastic polyurethane, which comprises the following raw materials in parts by mass:

[0007] (a) Polyol: 50 - 80 parts, preferably 55 - 70 parts;

[0008] (b) Polyisocyanate: 8 - 45 parts, preferably 10 - 40 parts;

[0009] (c) Chain extender: 6 - 30 parts, preferably 8 - 25 parts;

[0010] (d) Antioxidant: 0.5 - 8 parts, preferably 0.5 - 6 parts;

[0011] (e) Light stabilizer: 0.5 - 8 parts, preferably 0.5 - 6 parts;

[0012] Preferably, the chain extender includes a maleic anhydride-modified chain extender and an optional small molecule diol or diamine chain extender. The maleic anhydride-modified chain extender has the following structure:

[0013]

[0014] In the present invention, the maleic anhydride-modified chain extender is obtained by the esterification reaction of maleic anhydride and 1,4-butanediol.

[0015] The reaction mechanism is as follows:

[0016]

[0017] The molar ratio range of maleic anhydride to 1,4-butanediol is: n(maleic anhydride):n(butanediol) = 1.8 - 2.5:1;

[0018] In the present invention, an esterification catalyst can also be added during the esterification reaction of maleic anhydride and 1,4-butanediol, selected from one of strong acid catalysts and strong base catalysts, such as one or more of hydrochloric acid, sulfuric acid, sodium hydroxide, sodium ethoxide, etc.;

[0019] In the present invention, the esterification reaction temperature is 80 - 120 °C, the reaction time is 4 - 8 h, and after the reaction is completed, vacuum distillation is carried out to remove the unreacted monomers to obtain the maleic anhydride-modified chain extender;

[0020] In the present invention, the small molecule diol chain extender includes one or more of ethylene glycol, 1,2-propanediol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, and diethylene glycol; the diamine chain extender includes one or more of 1,3-propanediamine, 1,4-butanediamine, p-phenylenediamine, biphenylenediamine, and 3,3'-dimethyl-4,4-biphenylenediamine; preferably one or more of 1,4-butanediol, 1,6-hexanediol, and 3,3'-dimethyl-4,4-biphenylenediamine;

[0021] In the present invention, the mass ratio of the maleic anhydride modified chain extender to the small molecule diol or diamine is 1:0 to 1:10; preferably 1.0 to 5.0:1.

[0022] In the present invention, the polyol is one or more of polyether diol, polycarbonate diol, and polycaprolactone diol;

[0023] The polyether diol includes one or more of polyethylene oxide diol, polypropylene oxide diol, and polytetramethylene glycol with a molecular weight of 800-4000 g / mol, and more preferably polytetramethylene ether glycol with a number average molecular weight of 1000-4000 g / mol;

[0024] The polycarbonate diol is a macromolecular polymer with terminal hydroxyl groups at both ends of the long-chain molecule and repeating carbonate groups in the main chain, which is prepared by reacting a small molecule diol as an initiator with an aliphatic carbonate such as dimethyl carbonate, diethyl carbonate, ethylene carbonate, etc.; common initiators include 1,2-ethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, etc., and preferably 1,2-ethylene glycol, 1,4-butanediol, and neopentyl glycol; preferably the number average molecular weight range is 500-4000 g / mol, and more preferably 1000-4000 g / mol;

[0025] The polycaprolactone diol is prepared by ring-opening polymerization of ε-caprolactone in the presence of a catalyst and an initiator. Common initiators include ethylene glycol, diethylene glycol, neopentyl glycol, etc. Preferably the number average molecular weight range is 500-4000 g / mol, and more preferably 800-4000 g / mol;

[0026] In the present invention, the polyisocyanate is one or more of aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates; including one or more of 1,6 - hexamethylene diisocyanate, 1,10 - decane diisocyanate, 1,3 - cyclohexane diisocyanate, 1,4 - cyclohexane diisocyanate, 2,4 - hexahydrotoluene diisocyanate, 2,6 - hexahydrotoluene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 2,4 - toluene diisocyanate, 2,6 - toluene diisocyanate, 2,4 - diphenylmethane isocyanate, 4,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5 - naphthalene diisocyanate, 1,4 - naphthalene diisocyanate, m - xylylene diisocyanate, diphenylmethane - 3,3'-dimethoxy - 4,4'-diisocyanate, preferably one or more of 4,4'-diphenylmethane diisocyanate and 2,6 - toluene diisocyanate;

[0027] In the present invention, the raw materials of the thermoplastic polyurethane further include a catalyst, and the catalyst is selected from basic compounds or organometallic catalysts; the basic compounds are selected from tertiary amine compounds, preferably triethylenediamine, triethylamine, N,N - methyldicyclohexylamine, N,N - dimethylcyclohexylamine, N - methylmorpholine, N - ethylmorpholine, N - N'-dimethylpiperazine, N - N'-diethylpiperazine, 1,1,3,3 - tetramethylpiperidine, bis(2 - dimethylaminoethyl) ether, tetramethylbutanediamine, dimethylethanolamine, trimethylhydroxyethyl ethylenediamine, pentamethyldipropylenetriamine, 2,4,6 - tris(dimethylaminomethyl)phenol; the organometallic catalysts are selected from stannous octoate, dibutyltin dilaurate, zinc isooctanoate, zinc oleate, zinc naphthenate, bismuth naphthenate, cobalt naphthenate; preferably triethylenediamine, triethylamine, N,N - dimethylcyclohexylamine, stannous octoate, dibutyltin dilaurate, bismuth naphthenate;

[0028] Preferably, the mass concentration of the catalyst in the reaction system is 20 ppm - 150 ppm;

[0029] Preferably, the isocyanate index of the thermoplastic polyurethane preferably ranges from 0.97 to 1.03, and the isocyanate index is the molar ratio of the NCO group to the OH group in the raw materials.

[0030] Preferably, the antioxidant is selected from one or several of triethylene glycol bis - [3 - (3 - tert - butyl - 4 - hydroxy - 5 - methylphenyl)propionate], pentaerythritol tetra[β - (3,5 - di - tert - butyl - 4 - hydroxyphenyl)propionate], 2,6 - di - tert - butyl - 4 - methylphenol; the light stabilizer is selected from benzotriazole light stabilizers or hindered amine light stabilizers.

[0031] On the other hand, the present invention also provides a method for preparing a crosslinkable thermoplastic polyurethane, which comprises the following steps:

[0032] Step 1): Mix an antioxidant, a light stabilizer, an optional catalyst and a polyol to obtain mixture 1;

[0033] Step 2): Simultaneously inject a chain extender, mixture 1 and a polyisocyanate into a twin-screw extruder for reaction to obtain a TPU melt, and granulate to obtain a crosslinkable thermoplastic polyurethane material;

[0034] Preferably, first mix the maleic anhydride-modified chain extender with an optional small molecule diol or diamine chain extender evenly before use;

[0035] The mixing and stirring speed of the maleic anhydride-modified chain extender and the optional small molecule diol or diamine chain extender is 50-250 RPM, and the mixture of the two is preheated to 50-60 °C.

[0036] Preferably, in step 1), the mixing is carried out at a stirring speed of 80-180 RPM, and the mixing temperature is 100-120 °C.

[0037] Preferably, the twin-screw extruder in step 2) is divided into 10 temperature zones in total, the temperature range of the extruder is 80-250 °C, the length-diameter ratio of the extruder screw is 50-120:1, preferably a co-rotating double-headed screw meshing screw with a length-diameter ratio of 50-75:1, and the screw speed is 80-500 RPM.

[0038] The beneficial effects of the present invention are as follows:

[0039] (1) For the thermoplastic polyurethane material provided by the present invention, a special chain extender with reversible crosslinking bonds is first prepared through the esterification reaction of maleic anhydride and 1,4-butanediol, endowing the material with the characteristics of recyclable processing;

[0040] (2) The maleic anhydride-modified chain extender used in the thermoplastic polyurethane material provided by the present invention introduces reversible crosslinking bonds into the main chain of the thermoplastic polyurethane. During synthesis, its dosage can be adjusted by changing the raw material ratio, thereby adjusting the crosslinking degree of the thermoplastic polyurethane and improving the heat resistance and solvent resistance of the product. Description of the Drawings

[0041] Figure 1 It is the NMR spectrum of the maleic anhydride-modified chain extender of the present invention. Detailed Embodiments

[0042] The present invention will be further described below in conjunction with specific embodiments.

[0043] Raw Materials

[0044] Examples 1 - 7: The feeding ratios of the raw materials for preparing the polyurethane are shown in the following table:

[0045] Synthesis of maleic anhydride - modified chain extender:

[0046] 1,4 - butanediol and maleic anhydride were added to the reactor for preheating according to the molar ratio: n(maleic anhydride):n(butanediol) = 2:1. When the preheating temperature reached 75°C, 25 ppm of sodium hydroxide was added to the reactor, and then the reaction was carried out at 100°C for 8 h. The reaction was stopped, and the unreacted excess monomers were removed by vacuum distillation to obtain the maleic anhydride - modified chain extender.

[0047] The structure of the maleic anhydride - modified chain extender is as follows:

[0048]

[0049] Nuclear magnetic resonance was used to characterize the structure of the synthesized product to verify whether the maleic anhydride - modified chain extender with the expected structure was synthesized; the C - spectrum in the nuclear magnetic resonance spectrometer of model Bruker AV400FF was used to analyze the molecular structure of the chain extender. The test conditions were as follows: the sample concentration > 10 mg / mL, and scanned 400 times under the condition that the scanning pulse was 4.8 s; the nuclear magnetic resonance analysis results were as follows:

[0050] The preparation method of the examples is as follows:

[0051] The maleic anhydride - modified chain extender and diol were stored in the chain extender heat - preservation tank, and the temperature was maintained at 55°C. After stirring thoroughly for 10 - 20 min, mixture 1 was obtained and reserved for use;

[0052] The antioxidant, light stabilizer, optional catalyst and polyol macromolecular polyol were placed in the heat - preservation tank, and the temperature was maintained at 110°C. After stirring thoroughly for 200 min, mixture 2 was obtained and reserved for use;

[0053] Mixture 1, mixture 2 and polyisocyanate were simultaneously injected into a twin - screw extruder and reacted within the range of 100°C - 200°C to generate a TPU melt. After underwater pelletizing, a cross - linkable thermoplastic polyurethane material was obtained. The aspect ratio of the extruder was 52:1, and it was divided into 10 temperature zones in total. Temperature zones 1 - 3 were mixing sections, temperature zones 4 - 7 were reaction sections, and temperature zones 8 - 10 were conveying sections. The temperature settings of the mixing section in zones 1 - 3 were 110°C, 130°C, and 140°C in sequence, the temperature settings of the reaction section in zones 4 - 7 were 160°C, 180°C, 185°C, and 190°C in sequence, and the temperature settings of the conveying section in zones 8 - 10 were 185°C, 180°C, and 180°C in sequence;

[0054] Examples 1 - 6 and Comparative Example 1, the feeding mass ratios are shown in the following table:

[0055] POL: PolyTHF (polytetrahydrofuran diol); Diisocyanate: MDI; Chain extender 1: BDO; Chain extender 2: HDO

[0056]

[0057]

[0058] The products TPU1 - 7 obtained from Examples 1 - 7 were compared and tested with Comparative Examples 1 - 2, and the experimental results are as follows:

[0059]

[0060] Tensile strength test standard: ASTM - D128

[0061] Thermal overload test standard: ISO - 6722 Class C wire

[0062] It can be seen from the comparison of this group of experiments that as the proportion of maleic anhydride - modified chain extender decreases, the product performance decreases, but its thermal overload performance does not decline; considering the comprehensive performance, the mixing ratio of chain extender 1 and maleic anhydride - modified chain extender is ≤10:1;

[0063] The preparation methods of Examples 8 - 10 are the same as those of Example 1, except for different raw materials. The specific feeding ratios are shown in the following table:

[0064]

[0065]

[0066] POL1: PolyTHF (polytetrahydrofuran diol); POL2: PCDL - 2000 (polycarbonate diol); POL3: PLACCEL 200 (polycaprolactone diol); Diisocyanate: MDI; Chain extender 1: BDO

[0067] The products TPU10 - 12 obtained from Examples 8 - 10 were compared and tested with Comparative Examples 3 - 4, and the experimental results are as follows:

[0068]

[0069] It can be seen from the comparison of this group of experiments that under the same addition ratio of special chain extenders, obvious effects are achieved in different raw material systems, which is significantly helpful for improving the heat - resistance performance of the products.

[0070] Through the design of the chain extender structure and the adjustment of the mixing ratio, the present invention has improved the problems of poor heat resistance and inability to be recycled after cross - linking of existing TPU products. The TPU prepared by this method can be widely applied to fields such as automotive cables, wire and cables, and seals, and the products have excellent performance.

[0071] As described above, it is only the preferred embodiment of the present invention and does not impose any formal restrictions on the present invention. Any minor changes, modifications, and equivalent variations made by those skilled in the art within the scope of the technical solution of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention. At the same time, any equivalent changes, modifications, and variations made to the above embodiments based on the essential technology of the present invention still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A crosslinkable thermoplastic polyurethane, characterized in that, It comprises the following raw materials in parts by mass: (a) Polyol: 50 - 80 parts, preferably 55 - 70 parts; (b) Polyisocyanate: 8 - 45 parts, preferably 10 - 40 parts; (c) Chain extender: 6 - 30 parts, preferably 8 - 25 parts; (d) Antioxidant: 0.5 - 8 parts, preferably 0.5 - 6 parts; (e) Light stabilizer: 0.5 - 8 parts, preferably 0.5 - 6 parts.

2. The thermoplastic polyurethane according to claim 1, wherein The chain extender includes maleic anhydride modified chain extender and optionally a small molecule diol or diamine chain extender; Preferably, the maleic anhydride modified chain extender has the structure shown below:

3. The thermoplastic polyurethane according to claim 2, wherein The maleic anhydride modified chain extender is prepared by the esterification reaction of maleic anhydride and 1,4 - butanediol; Preferably, the molar ratio range of maleic anhydride to 1,4 - butanediol is: n(maleic anhydride):n(butanediol) = 1.8 - 2.5:1; Preferably, an esterification catalyst is added to the esterification reaction of maleic anhydride and 1,4 - butanediol, selected from one or more of strong acid catalysts and strong base catalysts, preferably one or more of hydrochloric acid, sulfuric acid, sodium hydroxide, and sodium ethoxide; Preferably, the esterification reaction temperature is 80 - 120 °C and the reaction time is 4 - 8 h.

4. The thermoplastic polyurethane according to claim 2 or 3, characterized in that, The small molecule diol chain extender includes one or more of ethylene glycol, 1,2 - propanediol, 1,4 - butanediol, 1,6 - hexanediol, neopentyl glycol, and diethylene glycol; the diamine chain extender includes one or more of 1,3 - propanediamine, 1,4 - butanediamine, p - phenylenediamine, benzidine, and 3,3’ - dimethyl - 4,4 - biphenylenediamine; preferably one or more of 1,4 - butanediol, 1,6 - hexanediol, and 3,3’ - dimethyl - 4,4 - biphenylenediamine; Preferably, the mass ratio of the maleic anhydride modified chain extender to the small molecule diol or diamine is 1:0 - 1:10; preferably 1.0 - 5.0:

1.

5. The thermoplastic polyurethane according to any one of claims 1-4, characterized in that, The polyol is one or more of polyether diol, polycarbonate diol, and polycaprolactone diol; Preferably, the polyether diol includes one or more of polyethylene oxide diol, polypropylene oxide diol, and polytetramethylene glycol with a molecular weight of 800 - 4000 g / mol, and more preferably polytetramethylene ether glycol with a number average molecular weight of 1000 - 4000 g / mol; Preferably, the polycarbonate diol has a number average molecular weight of 500 - 4000 g / mol, and more preferably 1000 - 4000 g / mol; Preferably, the polycaprolactone diol has a number average molecular weight of 500 - 4000 g / mol, and more preferably 800 - 4000 g / mol; Preferably, the polyisocyanate is one or more of aliphatic polyisocyanates, alicyclic polyisocyanates, and aromatic polyisocyanates; including one or more of 1,6 - hexamethylene diisocyanate, 1,10 - decane diisocyanate, 1,3 - cyclohexane diisocyanate, 1,4 - cyclohexane diisocyanate, 2,4 - hexahydrotoluene diisocyanate, 2,6 - hexahydrotoluene diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,2'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, 2,4 - toluene diisocyanate, 2,6 - toluene diisocyanate, 2,4 - diphenylmethane isocyanate, 4,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane diisocyanate, 1,5 - naphthalene diisocyanate, 1,4 - naphthalene diisocyanate, m - xylylene diisocyanate, diphenylmethane - 3,3'-dimethoxy - 4,4'-diisocyanate, preferably one or more of 4,4'-diphenylmethane diisocyanate and 2,6 - toluene diisocyanate.

6. The thermoplastic polyurethane according to any one of claims 1-5, characterized in that, The raw materials of the thermoplastic polyurethane further include a catalyst, and the catalyst is selected from basic compounds or organometallic catalysts; the basic compounds are selected from tertiary amine compounds, preferably triethylenediamine, triethylamine, N,N - methyl dicyclohexylamine, N,N - dimethylcyclohexylamine, N - methylmorpholine, N - ethylmorpholine, N - N'-dimethylpiperazine, N - N'-diethylpiperazine, 1,1,3,3 - tetramethylpiperidine, bis(2 - dimethylaminoethyl) ether, tetramethylbutanediamine, dimethylethanolamine, trimethylhydroxyethyl ethylenediamine, pentamethyldipropylenetriamine, 2,4,6 - tris(dimethylaminomethyl)phenol; the organometallic catalysts are selected from stannous octoate, dibutyltin dilaurate, zinc isooctanoate, zinc oleate, zinc naphthenate, bismuth naphthenate, cobalt naphthenate; Preferably, the catalyst is triethylenediamine, triethylamine, N,N - dimethylcyclohexylamine, stannous octoate, dibutyltin dilaurate, bismuth naphthenate; Preferably, the mass concentration of the catalyst in the reaction system is 20 ppm - 150 ppm; Preferably, the isocyanate index of the thermoplastic polyurethane is 0.97 - 1.03, and the isocyanate index is the molar ratio of NCO groups to OH groups in the raw materials. Preferably, the antioxidant is selected from one or several of triethylene glycol bis - [3-(3 - tert - butyl - 4 - hydroxyphenyl)propionate], pentaerythritol tetra[β-(3,5 - di - tert - butyl - 4 - hydroxyphenyl)propionate], 2,6 - di - tert - butyl - 4 - methylphenol; Preferably, the light stabilizer is selected from benzotriazole light stabilizers or hindered amine light stabilizers.

7. The preparation method of the thermoplastic polyurethane according to any one of claims 1-6, characterized in that, Comprising the following steps: Step 1): Mix the antioxidant, light stabilizer, optional catalyst and polyol to obtain mixture 1; Step 2): Inject the chain extender, mixture 1, and polyisocyanate into a twin - screw extruder simultaneously for reaction to obtain a TPU melt, and pelletize to obtain a cross - linkable thermoplastic polyurethane material; Preferably, the maleic anhydride modified chain extender is first mixed evenly with an optional small molecule diol or diamine chain extender before use; Preferably, the mixing and stirring speed of the maleic anhydride modified chain extender and the optional small molecule diol or diamine chain extender is 50 - 250 RPM, and the mixture of the two is preheated to 50 - 60 °C.

8. The preparation method according to claim 7, wherein, In step 1), the mixture is mixed at a stirring speed of 80 - 180 RPM, and the mixing temperature is 100 - 120 °C; Preferably, in step 2), the twin-screw extruder is divided into 10 temperature zones in total. The temperature range of the extruder is 80 - 250 °C, the length-diameter ratio of the extruder screw is 50 - 120:1, preferably a co-rotating double-headed thread meshing type screw with a length-diameter ratio of 50 - 75:1, and the screw speed is 80 - 500 RPM.

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