CN111876106B

CN111876106B - Preparation method of binary organic silicon system modified starch-based wood adhesive, product and application thereof

Info

Publication number: CN111876106B
Application number: CN202010808062.0A
Authority: CN
Inventors: 吴芹; 邵威龙
Original assignee: Qilu University of Technology
Current assignee: Qilu University of Technology
Priority date: 2020-08-12
Filing date: 2020-08-12
Publication date: 2021-09-17
Anticipated expiration: 2040-08-12
Also published as: CN111876106A

Abstract

The invention provides a preparation method of a binary organic silicon system modified starch-based wood adhesive, belonging to the technical field of adhesives. The preparation method comprises (1) preparing oxidized starch; (2) preparing sodium dodecyl sulfate and polyoxyethylene octyl phenol ether-10 into a composite emulsifier; (3) preparing itaconic acid, 3- (methacryloyloxy) propyl trimethoxy silane and 1, 2-bis (triethoxysilyl) ethane into a mixture according to a molar ratio of 1:0.08: 0.92; (4) pouring the compound emulsifier prepared in the step (2) into the mixture prepared in the step (3) to obtain an emulsion; (5) adding initiator ammonium persulfate into the emulsion prepared in the step (4) to obtain a mixture; (6) and (3) adding the mixture prepared in the step (5) into the oxidized starch solution prepared in the step (1), and discharging after the reaction is finished. The raw materials used in the preparation method are all nontoxic and environment-friendly materials, and the wet bonding strength of the starch can be obviously improved.

Description

Preparation method of binary organic silicon system modified starch-based wood adhesive, product and application thereof

Technical Field

The invention relates to the technical field of adhesives, in particular to a preparation method of a binary organic silicon system modified starch-based wood adhesive, and a product and application thereof.

Background

The starch adhesive is widely applied due to the advantages of easily available raw materials, low price, no toxicity, no harm, biodegradability and the like. Preparation and performance research of organosilicon modified cassava starch cross-linking agent, Hao, et al. From "Chinese Adhesives", vol.26, 12 th, 2017, 12 th month. The content is as follows: firstly, preparing oxidized cassava starch by using hydrogen peroxide to prepare starch milk with the concentration of 30%, uniformly stirring at 50 ℃, and heating to 90 ℃ for gelatinization for 30 min; then reducing the reaction temperature to 60 ℃, adding 1mL of tributyl phosphate, 1mL of ethylene glycol and 7.5mL of 10% PVA, dropwise adding ammonium persulfate and acrylamide under the condition of introducing nitrogen (dropwise adding within 3.5 h), dropwise adding vinyl triisopropoxysilane after 2h (dropwise adding within 1.5 h), continuing to react for 4h, cooling and discharging to prepare the starch adhesive modified by organic silicon. Under the influence of factors such as the dosage of organic silicon, the dosage of polyacrylamide, the dosage of an initiator and the reaction temperature, the bonding strength of the prepared adhesive is 4.65MPa, the water-resistant time at 60 ℃ is 32h, and the GB/T14732-plus 2006 standard is met. The reaction is essentially that oxidized starch is firstly grafted with acrylamide, and then silanol generated by hydrolyzing alkoxy in organic silicon reacts with carboxyl, so that the organic silicon is connected to the acrylamide and the starch.

The above documents have many disadvantages, namely that acrylamide, tributyl phosphate, ethylene glycol and PVA are used as raw materials, and are chemical raw materials and are not environment-friendly; secondly, single organic silicon is used for modification, so that the effect is poor; ③ the reaction mechanism of the preparation described in this document: the organic silicon forms a layer of shell layer structure on the surface of the polymer formed by graft copolymerization of starch molecules and acrylamide. The document describes the reason why the adhesive prepared has enhanced water resistance: the vinyl triisopropoxysilane has large isopropoxy group volume, large steric hindrance, small cohesive energy density, small surface tension and high Si-O bond energy, and can modify starch to form a net-shaped crosslinking structure so as to prevent water molecules from entering. This document does not fully verify the mechanism, but only makes an infrared test of 1019cm^-1There is a characteristic absorption peak of Si-O-C, demonstrating that the silicone has been grafted onto the starch molecule, which expression cannot be used as a mechanism for the strong water resistance of the adhesives prepared. The document only tests the water resistance of the adhesive, and does not test the wet bonding strength. In the literature, a test piece to be tested is soaked in warm water at the temperature of 60 +/-3 ℃, and the glue opening time is used as an index for evaluating the water resistance of the adhesive. The test is carried outThe method is completely different from a wet bonding strength test method, and cannot be used as an evaluation index of the adhesive with higher wet bonding strength.

The starch adhesive is widely applied due to the advantages of easily available raw materials, low price, no toxicity, no harm, biodegradability and the like. But are less useful in the field of wood processing because of the poor wet bond strength of starch adhesives, which is manifested by poor or even complete loss of bond strength in environments where water is present or soaked with water. Therefore, the modification of the starch to improve the wet bonding strength of the starch is very necessary, can replace aldehyde-containing adhesives and other petroleum-based adhesives which are widely applied in the field of wood processing at present, and solves the problems of raw material shortage, toxicity, harm, environmental pollution and the like in the production and use processes of the adhesives.

Disclosure of Invention

In view of the above, the invention aims to provide a preparation method of a binary organosilicon system modified starch-based wood adhesive, and a product and application thereof. According to the preparation method of the binary organic silicon system modified starch-based wood adhesive, the starch, the itaconic acid and the organic silicon are used as raw materials, other chemical raw materials are not used, the environment is protected, no pollution is caused, and the wet bonding strength of the adhesive is higher than the bonding strength index of the II-type plywood specified by GB/T9846-one 2015.

In order to achieve the above purpose, the invention provides the following technical scheme:

the invention provides a preparation method of a binary organic silicon system modified starch-based wood adhesive, which comprises the following steps;

(1) preparing oxidized starch solution;

(2) preparing sodium dodecyl sulfate and polyoxyethylene octyl phenol ether-10 into a composite emulsifier;

(3) preparing itaconic acid, 3- (methacryloyloxy) propyl trimethoxy silane and 1, 2-bis (triethoxysilyl) ethane into a mixture according to a molar ratio of 1:0.08: 0.92;

(4) pouring the compound emulsifier prepared in the step (2) into the mixture prepared in the step (3), and stirring at room temperature to ensure that the mixture is transparent from turbid to obtain an emulsion; the mass percent of the sodium dodecyl sulfate in the emulsion is 1.2-2.1%; the polyoxyethylene octyl phenol ether-10 accounts for 0.8 to 1.4 percent of the mass percent of the emulsion;

(5) adding initiator ammonium persulfate into the emulsion prepared in the step (4) to obtain a mixture; the initiator ammonium persulfate accounts for 5-7.5% of the mass of the itaconic acid;

(6) adding the mixture prepared in the step (5) into the oxidized starch solution prepared in the step (1), heating to 65-80 ℃, reacting for 12-22 h, and discharging after the reaction is finished;

the oxidized starch solution in the step (1) accounts for 30-70% of the raw material by mass.

Preferably, the mass percentage of the sodium dodecyl sulfate in the emulsion (4) is 1.8%; the polyoxyethylene octyl phenol ether-10 accounts for 1.2 percent of the mass of the emulsion; the heating temperature of the initiator ammonium persulfate in the step (5) is 70 ℃, the reaction time is 17 hours, and the mass percentage of the oxidized starch in the step (1) in the raw material content is 60%.

Preferably, a magnetic stirrer with the model number of DF-101S is used in the step (4) to stir for 1.5h at the rotating speed of 200 r/min.

Preferably, in the step (6), the mixture prepared in the step (5) is added into the oxidized starch solution prepared in the step (1) by a peristaltic pump, the dripping time is 1.5h, nitrogen is introduced, an oil bath kettle is used for heating, a digital display overhead type electronic stirrer with the model number of OS40-Pro is used for controlling the stirring speed to be 200r/min, and the mixture is cooled and discharged after the reaction is finished.

The invention also provides the binary organosilicon system modified starch-based wood adhesive prepared by the preparation method of the binary organosilicon system modified starch-based wood adhesive.

The invention also provides the application of the binary organosilicon system modified starch-based wood adhesive prepared by the preparation method of the binary organosilicon system modified starch-based wood adhesive in bonding wood, metal, glass and paper.

Preferably, the hot pressing step is included, the hot pressing temperature is 175 ℃, the hot pressing time is 40min, and the hot pressing pressure is 1.6 Mpa.

The invention takes itaconic acid as a cross-linking agent and takes a compound organic silicon system as a modifier to prepare the starch-based adhesive, thereby improving the bonding strength and the water resistance of the starch-based adhesive. The two raw materials are selected for the following reasons:

(1) the organic silicon (organic silicon compound) has the advantages of high temperature resistance, weather resistance, water resistance and the like, and can be used for improving the bonding strength and the water resistance of the adhesive. At present, the organic silicon is mostly applied to improve the performance of the adhesive in a form of blending addition. There is no report about the modification of starch adhesive by organosilicon through graft copolymerization and the research of its reaction mechanism.

(2) Itaconic acid (itaconic acid) contains unsaturated double bond and has active chemical property. The organic silicon is an oil-soluble substance, and the probability of direct grafting to the water-soluble starch is low. However, the water-soluble itaconic acid is used as a cross-linking agent, one end of the molecule can chemically react with starch, and the other end of the molecule can be opened through double bonds to have a polymerization reaction with organic silicon containing double bonds, so that the starch and the organic silicon are connected, and a network connection structure between the starch and the organic silicon is increased, thereby further enhancing the bonding strength and the water resistance of the adhesive. Itaconic acid is obtained by biological fermentation, and is considered as a green bio-based chemical raw material which can be continuously developed. The itaconic acid has some applications in the aspect of preparing resin adhesives or polyester adhesives, but no relevant reports are found in the research of improving the starch adhesives, and more research spaces are still left in the field.

The influence of the preparation method of the binary organic silicon system modified starch-based wood adhesive on the wet bonding strength is researched; furthermore, the adhesive prepared by the preparation method of the binary organic silicon system modified starch-based wood adhesive is applied to bonding wood, metal, glass and paper, the influence change of hot pressing conditions on the wet bonding strength of the adhesive is researched, and the adhesive is helpful for practical application. The invention has the following advantages:

(1) the wet bonding strength of the starch is obviously improved. The starch has weak bonding capability, and the wet bonding strength of the starch is remarkably improved by selecting and proportioning raw materials, optimizing preparation process conditions and subsequent hot pressing conditions.

(2) And the organosilicon compound system is used, so that the polymer is endowed with higher binding power and water resistance. In the invention, two types of organic silicon, namely 3- (methacryloyloxy) propyl trimethoxy silane and 1, 2-di (triethoxysilyl) ethane, are compounded for use. The two have different functions, wherein the 3- (methacryloyloxy) propyl trimethoxy silane contains C ═ C double bonds, can perform free radical polymerization reaction of the double bonds with itaconic acid, and is grafted on starch; the 1, 2-di (triethoxysilyl) ethane does not contain C ═ C double bonds, although the C ═ C double bonds can not be directly reacted with itaconic acid, silicon hydroxyl generated by hydrolysis of the 1, 2-di (triethoxysilyl) ethane can generate dehydration condensation reaction with silicon hydroxyl generated by hydrolysis of 3- (methacryloyloxy) propyl trimethoxy silane to generate a small amount of Si-O-Si network hydrophobic structures, especially a large amount of Si-O-Si network hydrophobic structures can be generated in a system after hot pressing treatment, so that the polymer has higher molecular weight, strength and water resistance.

(3) The operation fully considers the use environment of the starch-based adhesive prepared by the invention, namely hot pressing, can further dehydrate and condense Si-OH bonds in the adhesive into Si-O-Si bonds, and enriches the content of the Si-O-Si bonds.

(4) The itaconic acid can obviously improve the graft copolymerization degree of starch and organic silicon, and the itaconic acid is a biomass material and is environment-friendly and degradable.

(5) The raw materials are all nontoxic and environment-friendly materials, and the main agent is a biomass material.

(6) The synthetic reaction system uses water to replace an organic solvent, and is green and environment-friendly.

Drawings

FIG. 1 is a flow chart of the preparation of a binary organosilicon system modified starch-based wood adhesive;

in FIG. 1, St- -starch, IA- -itaconic acid, OSt- -oxidized starch, APS- -initiator, SDS- -sodium dodecyl sulfate, OP-10- -polyoxyethylene octylphenol ether-10, BTESE- -1, 2-bis (triethoxysilyl) ethane, MEMO- -3- (methacryloyloxy) propyltrimethoxysilane, IA-M/B- -IA, MEMO, BTESE mixture dispersed in SDS/OP-10 composite emulsifier, composite emulsifier consisting of SDS/OP-10- -SDS and OP-10, IA-M/B-OSt- -itaconic acid and silicone modified starch based adhesive, IA-M/B + APS- -IA-M/B and APS mixture, IA/MEMO/BTESE- -a mixture of IA, MEMO, and BTESE;

FIG. 2 is a preparation of a wood board test piece

FIG. 3 is the effect of preparation conditions on the viscosity and wet bond strength of IA-M/B-OSt adhesive

In FIG. 3, the left column is measured for Wet bond strength (Wet bond strength), and the right column is measured for viscosity (viscocity);

FIG. 4 is a scanning electron microscope image of IA-M/B-OSt adhesive and distribution diagrams of elements C, O, and Si;

FIG. 5 is an infrared spectroscopic analysis of the constituent materials

FIG. 6 is a Raman spectrogram analysis during preparation of IA-M/B-OSt;

FIG. 7 shows the monomer components and the monomer polymers IA-M/B (APS)¹H NMR chart;

FIG. 8 shows OSt, IA-M/B (APS) and IA-M/B-OSt¹H NMR chart;

FIG. 9 shows thermogravimetric analysis of the IA-M/B-OSt adhesive;

FIG. 10 shows the effect of hot pressing conditions on wet bond strength and contact angle of IA-M/B-OSt adhesive;

FIG. 11 is Si 2p spectra before and after heat pressing of IA-M/B-OSt adhesive;

FIG. 12 shows the adhesive IA-M/B-OSt before and after hot pressing²⁹Si NMR chart;

FIG. 13 is an XRD pattern of IA-M/B-OSt adhesive before and after hot pressing;

FIG. 14 is an AFM image of IA-M/B-OSt adhesive before and after hot pressing.

Detailed Description

1. Experimental part

1.1 raw materials and chemicals for experiments

The modified starch adhesive (IA-M/B-OSt) is prepared by taking corn oxidized starch (OSt) as a main agent, 3- (methacryloxy) propyl trimethoxy silane (MEMO) and 1, 2-bis (triethoxysilyl) ethane (BTESE) as modifiers, Itaconic Acid (IA) as a cross-linking agent, Ammonium Persulfate (APS) as an initiator, Sodium Dodecyl Sulfate (SDS) and polyoxyethylene octyl phenol ether-10 (OP-10) as emulsifiers and finally carrying out graft copolymerization reaction on OSt, the MEMO, the BTESE and the IA.

The sources of the experimental raw materials in the invention are as follows:

corn starch (analytically pure, alatin), Ammonium Persulfate (APS) (analytically pure, alatin), 1, 2-bis (triethoxysilyl) ethane (BTESE) (≧ 95%, bifid medicine), Itaconic Acid (IA) (≧ 99%, alatin), 3- (methacryloyloxy) propyltrimethoxysilane (MEMO) (≧ 99.26%, bifid medicine), Sodium Dodecyl Sulfate (SDS) (analytically pure, seiko chemical reagent factory), polyoxyethylene octylphenol ether-10 (OP-10) (analytically pure, seiko chemical reagent factory), sodium hydroxide (analytically pure, seiko chemical reagent factory), 37% hydrochloric acid (HCl) (analytically pure, leiyang economic technology development area fine chemical factory), sodium hypochlorite (nao) (analytically pure, seiko fine chemical industry ltd).

1.2 preparation method of IA-M/B-OSt adhesive provided by the invention

The steps for preparing the IA-M/B-OSt adhesive are shown in figure 1, and the specific preparation method comprises the following steps:

(1) preparing oxidized starch solution;

(4) pouring the compound emulsifier prepared in the step (2) into the mixture prepared in the step (3), and stirring at room temperature to ensure that the mixture is transparent from turbid to obtain an emulsion; the sodium dodecyl sulfate accounts for 1.2 to 2.1 percent of the emulsion; the polyoxyethylene octyl phenol ether-10 accounts for 0.8 to 1.4 percent of the emulsion;

(5) adding initiator ammonium persulfate into the emulsion prepared in the step (4) to obtain a mixture; the initiator ammonium persulfate accounts for 5-7.5% of the itaconic acid;

the oxidized starch solution in the step (1) accounts for 30-70% of the raw material content.

In the invention, the optimal process parameters are as follows: the sodium dodecyl sulfate accounts for 1.8 percent of the emulsion in the step (4); the polyoxyethylene octyl phenol ether-10 accounts for 1.2 percent of the emulsion; the heating temperature of the initiator ammonium persulfate in the step (5) is 70 ℃, and the reaction time is 17 h.

In the invention, a magnetic stirrer with the model number of DF-101S is used in the step (4) and stirred for 1.5h at the rotating speed of 200 r/min.

In the invention, in the step (6), the mixture prepared in the step (5) is added into the oxidized starch solution prepared in the step (1) by using a peristaltic pump, the dripping time is 1.5h, nitrogen is introduced, an oil bath kettle is used for heating, a digital display overhead type electronic stirrer with the model number of OS40-Pro is used for controlling the stirring speed to be 200r/min, and the mixture is cooled and discharged after the reaction is finished.

In the invention, the invention also provides the binary organosilicon system modified starch-based wood adhesive prepared by the preparation method of the binary organosilicon system modified starch-based wood adhesive in the technical scheme.

The application of the binary organic silicon system modified starch-based wood adhesive in bonding wood, metal, glass and paper further comprises a hot pressing step, wherein the hot pressing temperature is 175 ℃, the hot pressing time is 40min, and the hot pressing pressure is 1.6 Mpa.

1.3 preparation of oxidized starch

In the invention, the corn starch is oxidized by NaClO, and the preparation of the oxidized starch can be configured according to the following preparation method, comprising the following steps:

firstly, preparing a 38% corn starch emulsion in a four-neck flask, placing the four-neck flask in a DF-101 water bath kettle, and controlling the stirring speed to be 500r/min by adopting an OS40-Pro digital display overhead electronic stirrer.

2 according to m_(NaClO)/m_(St)Sodium chlorate solution (NaClO) with a concentration of 10% was weighed out for an amount of 5% into a beaker.

③ prepare 0.1% concentration sodium hydroxide aqueous solution and place in another beaker.

And fourthly, dropwise adding the sodium hypochlorite solution prepared in the step III and the sodium hydroxide solution prepared in the step III into the four-neck flask containing the corn starch prepared in the step I by using 2 peristaltic pumps with the model number of BT100F, wherein the adding time is about 1 hour. Meanwhile, the temperature of the reaction system is gradually increased to 45 ℃ within 1h, the pH value is gradually increased to about 9.0, timing is started at the moment, and the reaction time is 2 h. During the reaction, the dropwise addition of the sodium hydroxide solution is continuously controlled to maintain the pH value of the reaction system at about 9.0.

And fifthly, after the reaction is finished, neutralizing the reaction product by using a hydrochloric acid solution with the concentration of 10% until the pH value is about 6.5, performing suction filtration and washing by using a Buchner funnel, performing freeze drying in a vacuum freeze dryer with the model of FD-A10N-50, and collecting a sample, namely the corn oxidized starch.

2. Single factor test method and determination method

The influence rule of the initiator dosage, the composite emulsifier dosage, the reaction temperature, the reaction time and the starch dosage on the viscosity and the wet gluing strength of the IA-M/B-OSt adhesive is examined by adopting a single-factor test method, and the single-factor test condition table is shown in table 1. Through m_(APS)/m_(IA)The amount of APS is controlled. The complex emulsifier (SDS/OP-10) is prepared by compounding SDS and OP-10 and passes through_(SDS)/m_(IA-M/B)、m_(OP-10)/m_(IA-M/B)Are respectively provided withThe amount of SDS and OP-10 was controlled. The single factor test conditions are shown in table 1 below:

2.1 method for determining Wet bond Strength

The invention relates to a method for measuring wet bonding strength of IA-M/B-OSt adhesive, which adopts the following measuring method:

2.1.1 preparation method of wood chip test piece

According to part 7 of plywood: cutting of test specimens (GB/T9846.7-2004) Wood board test pieces were prepared. Poplar boards having dimensions of 100mm (length) by 25mm (width) by 3mm (thickness) were sawn and treated in an oven at 40 ℃ for 4 hours to give a water content of about 7%. According to the method of '4.17 bond strength determination' in the test methods of physical and chemical properties of artificial boards and facing artificial boards (GB/T17657-2013), the prepared IA-M/B-OSt adhesive is mixed with a brush according to the ratio of 250g/M²The glue coating amount is evenly coated on the surface of the wood board, and then a hot press with the model of CREE-6014A is used for hot pressing. A wood board test piece for testing the bonding strength was fabricated as shown in fig. 2.

2.1.2 method for determining Wet bond Strength

The instrument model is as follows: electronic universal tester (Instron 5963)

The test method comprises the following steps: according to the requirements of test methods for evaluating the performance of artificial boards and surface decoration artificial boards (GB/T17657-2013), the wood chip test pieces prepared by 2.1.1 are treated as follows: first soaked in hot water at 63 deg.C for 3h, and then cooled at room temperature for 10 min. Using an electronic universal testing machine to carry out a tensile test on the wood chip test piece subjected to the soaking treatment, wherein the formula sigma is F_max(ii) the/S calculation, wherein: sigma is a shear force (unit: MPa) representing the bonding strength of the adhesive, F_maxThe maximum force value (unit: N) at the moment when the wood chip test piece is pulled open, and S is the bonding area of 625mm². And (3) testing conditions are as follows: stretchingThe rate was 500mm/min, room temperature.

2.2 Effect of autoclave conditions on the Performance of IA-M/B-OSt Adhesives

Preparing a wood chip test piece according to the mode shown in the figure 2, then carrying out hot pressing by using a hot press with the model of CREE-6014A under different temperatures, pressures and times, and analyzing the influence of the hot pressing temperature, the hot pressing time and the hot pressing pressure on the wet gluing strength and the hydrophobicity of the IA-M/B-OSt adhesive.

2.3 method of measuring viscosity

The instrument model is as follows: digital viscometer (NDJ-8s)

The test method comprises the following steps: the prepared adhesive samples were tested according to GB/T140740-2006. In a thermostatic water bath at 25 +/-0.5 ℃, placing the sample in a container with the diameter not less than 60mm and the height not less than 110mm, vertically immersing a rotor in the center of the sample, enabling the liquid level to reach the central marked line of a groove of the rotor, measuring each sample for three times, and taking the minimum reading value in the three-time sample test to be accurate to 1mPa & s.

Method for purifying 2.4 IA-M/B-OSt adhesive

The invention provides a purification method of an IA-M/B-OSt adhesive, which comprises the following steps: putting an IA-M/B-OSt adhesive sample into a50 ml centrifuge tube, adding 40ml absolute ethyl alcohol, performing ultrasonic oscillation for 10min, putting the centrifuge into a centrifuge for separation, pouring out the upper layer liquid, reserving the lower layer sample, performing freeze drying after repeating the operation for five times to prepare a purified sample, and performing a series of characterization tests.

2.5 characterization test

2.5.1 SEM and energy Spectroscopy

The instrument model is as follows: desk type scanning electron microscope (EM 30plus +, COXEM)

The test method comprises the following steps: and carrying out gold spraying treatment on a sample, and observing the sample under a desktop scanning electron microscope. And (4) taking the better imaged part to carry out C, O, Si three-element analysis to obtain an energy spectrum.

And (3) testing conditions are as follows: the acceleration voltage was 10 kV.

2.5.2 FT-IR analysis

The instrument model is as follows: fourier Infrared Spectroscopy (Bruker Tensor 37, Germany)

The test method comprises the following steps: taking a certain amount of sample, uniformly mixing with KBr according to the mass ratio of 1:70, tabletting, and carrying out infrared spectrum analysis.

And (3) testing conditions are as follows: the scanning range is 600cm^-1To 4000cm^-1Resolution of 4cm^-1And the number of scanning times is 32.

2.5.3 Confocal Raman analysis

The instrument model is as follows: laser confocal Raman spectrometer (InVia reflex, Renishaw)

The test method comprises the following steps: placing a small amount of freeze-dried samples on a glass slide, adjusting a coarse quasi-focus spiral and a fine quasi-focus spiral to enable the samples to be clear under a microscope, wherein the laser intensity is 5-10% and is 500cm^-1～2500cm^-1And performing point scanning to obtain a Raman spectrogram.

And (3) testing conditions are as follows: no. 532 laser

2.5.4 ¹H NMR analysis

The instrument model is as follows: nuclear magnetic resonance spectrometer (AVANCE II 400, Bruker)

The test method comprises the following steps: and (3) putting a small amount of dehydrated and dried sample into a nuclear magnetic tube, adding a solvent of deuterated DMSO, heating to dissolve, placing the sample in a nuclear magnetic instrument, and operating software to test.

And (3) testing conditions are as follows: deuterated DMSO was used, TMS as internal standard.

2.5.5 thermal weight (TG) and Differential Scanning Calorimetry (DSC) thermodynamic properties

The instrument model is as follows: synchronous thermal analyzer (STA 449F 3, netzsch)

The test method comprises the following steps: and (3) putting a sample with the mass of 5-15 mg into an alumina crucible, adopting an internal balance weighing method to obtain the accurate sample mass, and operating software to perform experiments.

And (3) testing conditions are as follows: temperature rise range (30-600 ℃), temperature rise rate (10K/min), experimental crucible type (alumina crucible)

2.5.6 contact Angle

The instrument model is as follows: full-automatic video optical contact angle measuring instrument (OCA50, Datrysics)

The test method comprises the following steps: the prepared adhesive is mixed according to the ratio of 350g/m²Coating on single-sided poplar board, and applying polytetrafluoroethylene on the other sideCovering the ethylene grinding tool, preparing the single-side coated plywood under a certain hot-pressing condition, selecting five different positions for testing each plywood, recording the experimental value measured each time, and finally calculating the average value to measure the hydrophobic property of the cured surface of the adhesive.

And (3) testing conditions are as follows: the amount of water droplets was 5. mu.l.

2.5.7X-ray photoelectron Spectroscopy (XPS)

The instrument model is as follows: x-ray photoelectron spectroscopy (ESCABXi +, THERMO).

The test method comprises the following steps: and (4) placing a small amount of dried samples in an aluminum foil for pressing and processing, and testing.

2.5.8 solid nuclear magnetic resonance spectrum (²⁹Si NMR)

The instrument model is as follows: solid nuclear magnetic resonance spectrometer (JNM ECZ600R, JEOL)

The test method comprises the following steps: and (3) taking a small amount of dehydrated and dried solid sample to test in an instrument to obtain a 29Si NMR spectrum.

2.5.9X-ray diffraction (XRD)

The instrument model is as follows: x-ray diffractometer (D8-ADVANCE, Bruker)

The test method comprises the following steps: freeze-drying the sample, grinding into powder, and placing on an XRD sample table for testing.

And (3) testing conditions are as follows: the target material is Cu Ka, the tube current is 40mA, the tube voltage is 40KV, the step length is 0.02 degree, the scanning speed is 10 degrees/min, and the scanning range 2 theta is 5-80 degrees

2.5.10 Transmission Electron microscope (AFM)

The instrument model is as follows: transmission electron microscope (JEM 2100, JEOL)

The test method comprises the following steps: the prepared adhesive is mixed according to the ratio of 350g/m²Coating the single-sided poplar board with the adhesive on the surface of the single-sided poplar board, covering the other surface of the single-sided poplar board with a polytetrafluoroethylene grinding tool, preparing the single-sided coated plywood under certain hot-pressing conditions, and then testing.

3 test results and analysis

3.1 Effect of preparation conditions on the Properties of IA-M/B-OSt Adhesives

3.1.1 APS dosage

APS is an initiator, is easy to be decomposed by heat to generate free radicals, can be used for initiating the free radical polymerization reaction of vinyl monomer emulsion, and can also be used for the crosslinking curing and high polymer crosslinking reaction of unsaturated polyester. With the increase of the amount of APS, the viscosity and the wet bond strength of the adhesive both tend to increase and decrease, as shown in fig. 3 (a).

When the initiator APS is not used, free radicals are not generated in the reaction system, the OSt, IA and organosilicon hardly undergo polymerization, the viscosity is mainly provided by OSt, and the wet bond strength is very low. When the dosage of APS is gradually increased, under the initiation action of free radicals generated by APS, the OSt, IA and organosilicon generate graft copolymerization reaction, the molecular weight of the product is gradually increased, the viscosity is increased, and the wet bonding strength is also increased. However, as the amount of APS continues to increase, excess free radicals are generated which can break the glycosidic bond of OSt, resulting in a decrease in the molecular weight of OSt; in addition, as the amount of APS is increased, although the generation rate of free radicals is increased, the chain termination rate is also increased, so that the time for the graft copolymerization reaction of OSt, IA and organosilicon is shorter, the chain growth amplitude is smaller, and the molecular weight of the product is lower. The above factors combine to result in a product with reduced viscosity and reduced wet bond strength. When m is_(APS)/m_(IA)The wet bonding strength of the prepared IA-M/B-OSt adhesive is 5-7.5% and exceeds 0.7MPa specified in the national standard GB/T17657-2013. When m is_(APS)/m_(IA)When the wet adhesive strength is 7.5 percent, the wet adhesive strength of the prepared IA-M/B-OSt adhesive is the maximum, and is 0.8377 MPa.

3.1.2 amount of composite emulsifier (SDS/OP-10)

The emulsifier is used for uniformly dispersing oily organic silicon in a water system so as to be mutually soluble with water-soluble IA and starch. As the amount of the complex emulsifier (SDS/OP-10) was increased, both the viscosity and the wet bond strength showed a tendency to increase and then decrease, as shown in FIG. 3 (b).

The oily organosilicon can not fully contact with water-soluble IA molecules and OSt molecules without using an emulsifier, the degree of graft copolymerization reaction of the components is low, the molecular weight of the product is low, the viscosity is low, and the wet bonding strength is low. With the increase of the dosage of the emulsifier, the contact probability of the organic silicon with the IA molecules and the OSt molecules is increased, namelyThe components (organic silicon, IA and OSt) can better participate in graft copolymerization reaction, the molecular weight of the product is increased, the viscosity is improved, and the wet bonding strength is improved. However, when the amount of the emulsifier is too high, the component substances are excessively diluted, and the collision between monomers is reduced, so that the degree of graft copolymerization is reduced, the molecular weight of the product is low, and the bonding strength is reduced. When m is_(SDS)/m_(IA-M/B)1.2% -2.1%, m_(OP-10)/m_(IA-M/B)When the wet adhesive strength is 0.8-1.4%, the wet adhesive strength of the prepared IA-M/B-OSt adhesive exceeds 0.7MPa specified in the national standard GB/T17657-2013. When m is_(SDS)/m_(IA-M/B)1.8% of m_(OP-10)/m_(IA-M/B)When the wet adhesive content is 1.2%, the wet bonding strength of the prepared IA-M/B-OSt adhesive is the maximum, and is about 0.9535 MPa.

3.1.3 reaction temperature

As shown in fig. 3(c), the viscosity of the IA-M/B-OSt adhesive gradually increased with the increase of the reaction temperature, and the wet bond strength tended to increase first and then decrease.

The temperature is increased, and the free radicals generated by the APS are increased, which is helpful for initiating the graft copolymerization reaction among OSt, AI and organosilicon. However, as the temperature continues to rise, too many free radicals generated by APS may initiate self-polymerization of some reactive monomers AI or silicone, which is detrimental to graft copolymerization with OSt. When the reaction temperature is 65-80 ℃, the wet bonding strength of the prepared IA-M/B-OSt adhesive exceeds 0.7MPa specified in the national standard GB/T17657-2013. When the reaction temperature is 70 ℃, the viscosity of the prepared adhesive is about 7690mPa & s, and the maximum wet bonding strength is about 1.0967 MPa.

3.1.4 reaction time

As shown in FIG. 3(d), the viscosity of IA-M/B-OSt increased gradually with increasing reaction time, while the wet bond strength increased first and then decreased.

At the beginning of the reaction, the molecular weight of the graft copolymerization product is increased continuously along with the reaction, the viscosity is increased, and the wet bonding strength is increased. When the graft copolymerization reaction between IA, silicone, and OSt is completed, if it is continued for a prolonged period of time, dehydration condensation reaction between the silicon hydroxyl groups occurs to form Si — O-Si structure, viscosity is further increased, but wet bond strength is decreased. In conclusion, when the reaction time is 12h-22h, the wet bonding strength of the prepared adhesive exceeds 0.7MPa specified in the national standard GB/T17657-2013. When the reaction time is 17 hours, the viscosity of the prepared adhesive is about 7690mPa & s, and the maximum wet bonding strength is about 1.0967 MPa.

3.1.5 amount of oxidized starch (OSt)

As shown in fig. 3(e), as the OSt content increased, the viscosity increased and the wet bond strength increased because enough OSt could undergo graft copolymerization with more IA and silicone monomers to produce a copolymer product with a larger molecular weight and a richer network structure. However, the amount of OSt continued to increase, leaving an excess of unreacted OSt in the system, which had poor water resistance, and resulted in a slight decrease in wet bond strength. In conclusion, when the OSt is used in an amount of 30-70%, the wet bonding strength of the prepared adhesive exceeds 0.7MPa specified in the national standard GB/T17657-2013. When the amount of OSt is 60%, the viscosity of the adhesive is about 11060 mPa.s, and the maximum wet bonding strength is about 1.2205 MPa.

In conclusion, by studying the influence of the above different factors on the viscosity and wet bonding strength of the IA-M/B-OSt adhesive, the optimal preparation process conditions are obtained: initiator dosage m_(APS)/m_(IA)7.5%, the dosage of the composite emulsifier: m is_(SDS)/m_(IA-M/B)＝1.8％，m_(OP-10)/m_(IA-M/B)The reaction temperature is 70 ℃, the reaction time is 17h, the dosage of the oxidized starch is 60%, the viscosity of the IA-M/B-OSt adhesive prepared under the conditions is 11850mPa & s, and the wet bonding strength is 1.2815MPa at most.

3.2 SEM and energy Spectroscopy

The IA-M/B-OSt adhesive is purified and freeze-dried, and then subjected to energy spectrum analysis test. The experimental result is shown in fig. 4, the sample morphology is in a random state, and the elements of C, O, and Si contained in the sample are distributed relatively uniformly, which indicates that the prepared IA-M/B-OSt adhesive contains silicon elements, namely: silicones have been successfully grafted onto the molecular chain of oxidized starch.

3.3 FT-IR analysis

As shown in FIG. 5, 929cm in OSt infrared spectrum^-1And 860cm^-1Primary alcohols and methylene groups on the glucose unit structure, respectively. The infrared spectrum of MEMO and IA is at 1728cm^-1And (C) is a characteristic absorption peak of-O. 1728cm appears in an infrared spectrum of IA-M/B-OSt^-1Has an absorption peak at 929cm^-1And 860cm^-1The absorption peak disappears to 920cm^-1The characteristic absorption peak of Si-OH is shown, which fully indicates that the graft copolymerization of the MEMO, IA and OSt occurs, and the grafting position is located in the starch C₆Primary alcohol of the position.

3.4 Confocal Raman analysis

Samples with different reaction times (2h, 7h, 12h and 17h) are taken, freeze-dried and then subjected to confocal Raman testing. As shown in FIG. 6, the reaction time was 1078cm^-1The peroxy group (-O: O-) shows a tendency to gradually disappear, indicating that the initiator APS is gradually consumed; at 1644cm^-1The carbon-carbon double bond (-C ═ C-) at the site also shows a tendency to decrease gradually because, under the initiation of a radical, C ═ C-is gradually opened to C-and chain growth progresses, indicating that IA and MEMO participate in the polymerization reaction.

3.51H NMR analysis

To demonstrate the mechanism of the graft copolymerization reaction between silicone, IA and OSt, IA, MEMO, BTESE, IA-M/B (APS), and IA-M/B-OSt were characterized by 1H NMR, respectively, and the results are shown in FIGS. 7 and 8. IA-M/B (APS) is the polymerization product of IA, MEMO, BTESE under the action of an initiator.

IA. The position of the peak for each hydrogen of the MEMO and BTESE and the corresponding position in the formula are shown in FIG. 7. IA-M/B (APS) is an ammonium cation at-7.0 ppm triplet, which is a decomposition product of a persulfate initiator; the double-bond hydrogen of IA-M/B (APS) is still present between 5.5 ppm and 6.0ppm, because the free radical polymerization reaction is not completely finished, and partial monomers still remain in the system; IA-M/B (APS) splits off a plurality of peaks and appears an envelope peak at 1.0-1.3 ppm and 3.0-4.0 ppm respectivelyRespectively correspond to H₁₄And H₁₅The polymerization reaction of each monomer is shown to generate more carbon chains; peaks for the remaining monomers are still found in IA-M/B (APS), and some peaks are shifted, which is unavoidable in high molecular weight polymer systems.

As can be seen from FIG. 8, the-OH groups on C6 in IA-M/B-OSt disappeared significantly, and the-OH groups on C2 and C3 were also weakened considerably, indicating that the graft copolymerization of the respective monomers with OSt occurred mainly on C6 and secondly on C2 and C3. 5.5-6.0 ppm of double bond hydrogen in IA-M/B-OSt obviously disappears, which indicates that IA and MEMO containing double bonds all participate in graft copolymerization reaction. Peaks at 1.0-1.3 ppm and 3.0-4.0 ppm of IA-M/B (APS) also appear in IA-M/B-OSt, which shows that IA, organic silicon and OSt successfully carry out graft copolymerization reaction and prepare the IA-M/B-OSt adhesive.

3.6 thermogravimetric analysis

Thermogravimetric analysis was performed on the IA-M/B-OSt adhesive, as shown in FIG. 9. T is₁The endothermic reaction in the zone may be due to loss of water and evaporation from the sample. T is₂A section of slow weight loss exists between 140 ℃ and 200 ℃, and an endothermic reaction is accompanied, so that Si-O-Si is formed by dehydration condensation of-Si-OH in the IA-M/B-OSt adhesive, and when the temperature is 200 ℃, the weight loss rate of a sample is the maximum, and the degree of the endothermic reaction is the maximum. Enter T₃After the zone, the sample continued to lose weight with an endothermic reaction, probably due to excessive temperature leading to degradation of the adhesive. Therefore, the temperature should be controlled not to exceed 200 ℃ during the use of the IA-M/B-OSt adhesive.

3.7 influence of the Hot pressing conditions on the improvement of the Wet gluing Strength of the IA-M/B-OSt adhesive

3.7.1 hot pressing temperature

The experimental results are shown in fig. 10 (a). When the hot-pressing temperature is 100 ℃, the wet bonding strength of the IA-M/B-OSt adhesive is basically zero. With the increase of the hot-pressing temperature, the wet gluing strength gradually increases, and the contact angle also increases, because the hydrophilic-Si-OH structure in the IA-M/B-OSt adhesive is gradually dehydrated and condensed to form a hydrophobic Si-O-Si structure. The wet bond strength is greatest when the hot pressing temperature is around 175 ℃. However, as the temperature continues to increase, the internal structure of the wood is destroyed and the wood is blackened, and the fracture surface is a wood board instead of a glued surface. The above results show that the wet bond strength of the IA-M/B-OSt adhesive is greatly affected by the hot pressing temperature.

3.7.2 Hot pressing time

The experimental results are shown in fig. 10 (b). With the reaction time, the wet bonding strength and the contact angle of the IA-M/B-OSt adhesive show a trend of increasing and then stabilizing, which shows that along with the reaction time, the-Si-OH in the system is gradually dehydrated and condensed to form a hydrophobic Si-O-Si structure, so that the wet shear strength and the contact angle are increased. In summary, when the hot pressing time is about 40min, the bonding strength is maximized.

3.7.3 hot pressing pressure

The experimental results are shown in fig. 10 (c). As the hot pressing pressure increases, the wet bond strength and contact angle tend to increase and then decrease. If the hot-pressing pressure is too low, the adhesive is difficult to permeate into the wood, and barbs are difficult to form, so that the wet gluing strength is reduced; however, if the hot pressing pressure is high, the adhesive will be pressed out of the wood chip bonding layer, which also causes the wet bonding strength to decrease. In summary, when the hot pressing pressure is 1.6MPa, the wet bond strength is maximized.

In summary, the IA-M/B-OSt adhesive is applied under appropriate hot pressing conditions: the hot pressing temperature is 175 ℃, the hot pressing time is 40min, the hot pressing pressure is 1.6MPa, the maximum wet gluing strength is 1.2815MPa, and the contact angle is 135 degrees.

3.8 mechanism for improving wet bonding strength of IA-M/B-OSt adhesive by hot pressing

3.8.1 XPS spectra before and after hot pressing of IA-M/B-OSt adhesive

XPS test was performed on IA-M/B-OSt adhesive before and after hot pressing, and changes in the Si element functional group structure were analyzed, and the experimental results are shown in FIG. 11. The Si 2p spectrum contains three gaussian peaks, namely (Si-C, BE ═ 101.6eV), (Si-O-C, BE ═ 102.5eV), and (Si-O-Si, BE ═ 103.5 eV). The electron peak of the Si-O-Si functional group with the binding energy of about 103.5eV in the hot-pressing IA-M/B-OStSi 2p map is obviously enhanced, which shows that the IA-M/B-OSt generates more hydrophobic groups Si-O-Si by hot pressing, and the wet bonding strength is enhanced.

3.8.2 IA-M/B-OSt adhesive before and after hot pressing²⁹Si NMR

Samples of the IA-M/B-OSt adhesive in three states of' no hot-pressing curing, hot-pressing curing at 120 ℃ and hot-pressing curing at 175 ℃ are respectively subjected to²⁹Si NMR measurement was performed to analyze the change in the structure of the functional group containing Si element, and the results are shown in FIG. 12. Of three samples²⁹Si NMR spectra show that a clear signal exists between-45 ppm and-120 ppm, and the peak position is deviated from that of pure BTESE (-45 to-75) due to the existence of two different organic silicon and other active functional groups in the system. T of IA-M/B-OSt adhesive with increasing hot pressing temperature¹、T²Gradual signal peak attenuation, T³The signal peak is obviously enhanced, which shows that Si-OH gradually shrinks to synthesize Si-O-Si functional groups in the hot pressing process.

3.8.3 XRD pattern before and after hot pressing of IA-M/B-OSt adhesive

XRD testing was performed on IA-M/B-OSt samples at different autoclave temperatures, as shown in FIG. 13. With the increase of the hot pressing temperature, the sample gradually shows a sharp crystallization peak at about 22 degrees, which is a characteristic peak of silicon dioxide, and this shows that Si-OH is gradually dehydrated and condensed into a Si-O-Si structure with a crystal structure by the heat pressing of the IA-M/B-OSt adhesive.

3.8.4 AFM before and after IA-M/B-OSt adhesive hot pressing

The roughness of the sample surface may reflect its hydrophobicity. As shown in FIG. 14, compared with the morphology of the IA-M/B-OSt adhesive on the surface of the plywood pressed at normal temperature, the morphology of the IA-M/B-OSt adhesive after hot pressing is rougher, the roughness before hot pressing is 694nm, and the roughness after hot pressing is 1514nm, and the comparison of the roughness shows that the hydrophobic capacity is enhanced, so that the wet bonding strength of the plywood is enhanced.

In conclusion, the preparation method, the product and the application of the binary organic silicon system modified starch-based wood adhesive provided by the invention are characterized in that starch, itaconic acid and organic silicon are used as raw materials to prepare the starch-based adhesive which has high wet bonding strength, is nontoxic and has no pollution. The wet bonding strength of the starch-based adhesive prepared by the preparation method of the invention is up to 1.2815MPa, which is far higher than the bonding strength index of II-type plywood specified in the general plywood (GB/T9846-.

The invention applies SEM and energy spectrum analysis, FT-IR, Confocal Raman,¹H NMR and other characterization means show that a large amount of graft copolymerization reaction occurs between the organic silicon and the starch.

The IA-M/B-OSt adhesive prepared by the invention is greatly influenced by hot pressing conditions (temperature, time and pressure), and the optimal hot pressing parameters are as follows: the hot pressing temperature is 175 ℃, the hot pressing time is 40min, and the hot pressing pressure is 1.6 MPa.

The invention adopts XPS for characterization,²⁹Si NMR, XRD, AFM and other characterization means can prove that Si-OH bonds in the IA-M/B-OSt adhesive can be further converted into Si-O-Si bonds by hot pressing, which is the fundamental reason that the adhesive has higher wet bonding strength.

Claims

1. A preparation method of a binary organic silicon system modified starch-based wood adhesive is characterized by comprising the following steps;

(1) preparing oxidized starch solution;

2. The method for preparing the binary organosilicon system modified starch-based wood adhesive according to claim 1, wherein the sodium dodecyl sulfate accounts for 1.8% of the emulsion in the step (4); the polyoxyethylene octyl phenol ether-10 accounts for 1.2 percent of the mass of the emulsion; the heating temperature of the initiator ammonium persulfate in the step (5) is 70 ℃, the reaction time is 17 hours, and the mass percentage of the oxidized starch in the step (1) in the raw material content is 60%.

3. The preparation method of the binary organosilicon system modified starch-based wood adhesive according to claim 1, wherein in the step (4), a magnetic stirrer with the type DF-101S is used for stirring at a rotating speed of 200r/min for 1.5 h.

4. The preparation method of the binary organosilicon system modified starch-based wood adhesive according to claim 1, wherein in the step (6), the mixture prepared in the step (5) is added into the oxidized starch solution prepared in the step (1) by a peristaltic pump, the dripping time is 1.5h, nitrogen is introduced, an oil bath kettle is heated, a digital display overhead electronic stirrer with the model of OS40-Pro is used for controlling the stirring speed to be 200r/min, and the temperature is reduced and the material is discharged after the reaction is finished.

5. The two-component organosilicon system modified starch-based wood adhesive prepared by the preparation method of the two-component organosilicon system modified starch-based wood adhesive according to any one of claims 1 to 4.

6. Use of the dual silicone system modified starch based wood adhesive of claim 5 for bonding wood, metal, glass and paper.

7. The application of the binary organosilicon system modified starch-based wood adhesive in bonding wood, metal, glass and paper is characterized in that when wood is bonded, a hot press is adopted for hot pressing, the hot pressing temperature is 175 ℃, the hot pressing time is 40min, and the hot pressing pressure is 1.6 MPa.