CN112012013A

CN112012013A - Nano-cellulose toughened mixed fiber yarn composite material laminated plate and preparation method thereof

Info

Publication number: CN112012013A
Application number: CN202010927178.6A
Authority: CN
Inventors: 杨旭静; 方文俊
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2020-12-01
Anticipated expiration: 2040-09-07
Also published as: CN112012013B

Abstract

The invention provides a nano-cellulose toughened composite laminated board of mixed fiber yarn and a preparation method thereof. First, an electrostatically repelling dispersed oxidized nanofibrillated cellulose (toffc) is prepared; then, dipping a continuous glass fiber/random copolymerization polypropylene fiber (CGF/PPR) mixed yarn fabric by using a sol solution containing TONFC; and drying and hot press forming to obtain the composite laminated board. Esterification reaction and amidation reaction in the composite material system ensure the formation of strong TONFC/PPR and CGF/PPR interfaces and beta phase with raised material toughness. Thus, the inventive tobnfc toughened composite laminates have high mode i interlaminar fracture toughness. The invention has simple preparation process and high efficiency, effectively improves the interlaminar fracture toughness of the thermoplastic composite material, and opens up a new way for improving the interlaminar region toughness of the thermoplastic laminated board.

Description

Nano-cellulose toughened mixed fiber yarn composite material laminated plate and preparation method thereof

Technical Field

The invention relates to the technical field of thermoplastic composite materials, in particular to a mixed fiber yarn composite material laminated plate toughened by nano-cellulose and a preparation method thereof.

Background

Continuous glass fiber reinforced polypropylene (CGF/PP) composites have received much attention as a promising lightweight thermoplastic composite. Compared with the traditional thermosetting composite materials and metal materials, the composite materials have the remarkable advantages of high toughness, shorter manufacturing period and no need of cold storage. The dual advantages of high mechanical properties and low cost have prompted the partial replacement of some metal parts in automobiles by CGF/PP composites, and also have found widespread use in the marine and aerospace industries, and have brought enormous economic benefits, for example, a 10% weight reduction in motor vehicles can increase fuel economy from 6% to 8%, with more significant performance on aircraft. These significant advantages therefore make it possible for CGF/PP composites to find increasing use in future traffic components, as governments seek to address environmental and fossil fuel shortages by lightweight design of components while ensuring passenger safety.

In practical applications, CGF/PP composites use 2D laminate structures in order to maximize specific stiffness and specific strength, and despite their extraordinary mechanical properties in the in-plane direction, they are less resistant to interlaminar fracture in the thickness direction when subjected to loads from a number of different operating conditions. In the field of composite research, a great deal of experimental and analytical research has been devoted to improving the fracture toughness of laminated composite structures. Studies have shown that woven fabric laminates have higher damage tolerance in the presence of delamination than unidirectional laminates. However, the high production costs and the damage caused during the production and the reduction of the in-plane properties limit the use of this method.

Adding various micro-nano fillers into the complex system is considered to be a convenient and efficient method for remarkably improving the interlayer fracture toughness. If 3 wt% organoclay was filled into the PP matrix, the plain weave CGF/PP composite had significantly improved initial and extended fracture toughness by about 64% and 67%, respectively. Other nano-reinforcements, such as graphene oxide, multi-walled carbon nanotubes, graphite nanoplatelets, and nano-organic montmorillonite, also have the ability to significantly improve fracture toughness. It is noted, however, that the nanoparticles must first be heat fused with the bulk PP particles before the glass fiber strands or fabrics can be impregnated to toughen the interlaminar regions. Therefore, the melt impregnation toughening method is not applicable when the CGF/PPR blended yarn composite material is prepared by blending the toughened CGF fibers and the PP fibers. This also means that new nanomaterials and manufacturing processes need to be found to improve the interlaminar fracture toughness of the composite.

Cellulose, in turn, is a material that is abundantly present in nature in the form of Cellulose Nanocrystals (CNC), nanofibrillated cellulose (NFC), Cellulose Microcrystals (CMC) and Cellulose Microfibrils (CMFs). The cellulose has excellent mechanical properties (i.e. tensile strength (0.3-22GPa), modulus (58-180GPa) and low density (1.5 kg/m)³) Can meet the industrial requirements of green and sustainable development. In summary, we have found that the existing nanomaterial toughening, usually, a high-heat slurry prepared by melting and blending the nanomaterial and the matrix material in advance is needed to impregnate the glass fiber fabric, and the steps are complicated, the energy consumption is high, and the manufacturing cost is high. In addition, the existing melt blending adds the nano material into the composite material, which has the purpose of improving the interlayer fracture toughness to a certain extent, but can not overcome the defect of nano material agglomeration; on the other hand, the glass fiber in the middle of the glass fiber bundle is difficult to be impregnated by the melt, becomes the initial source of the defect and is not beneficial to improving the mechanical property. Therefore, in order to promote the rapid development of the material industry, the development of a low-cost and high-efficiency nano material toughened thermoplastic composite laminated board process is urgently needed.

Disclosure of Invention

The invention provides a mixed fiber yarn composite material laminated plate toughened by nano-cellulose and a preparation method thereof, and aims to provide a simple and effective method for improving the interlayer fracture toughness of a thermoplastic composite material laminated plate.

In order to achieve the above object, the present invention provides a nanocellulose-toughened hybrid fiber yarn composite laminate and a method for preparing the same, comprising the steps of:

1) preparation of oxidized nanofibrillated cellulose (toffc) sol solution:

preparing a TONFC sol solution containing independent dispersion by taking softwood pulp as a raw material and 2,2,6, 6-tetramethylpiperidine-1-oxynitride (TEMPO), sodium bromide and sodium hypochlorite as oxidants; hydroxyl at the C6 position of the nanofibrillated cellulose (NFC) is changed into carboxyl after oxidation, and the electrostatic repulsion brought by the carboxyl enables the TONFC to be independently dispersed in the sol liquid.

2) Sol impregnation:

impregnating continuous glass fiber/polypropylene random copolymer (CGF/PPR) mixed yarn fabric with the sol solution obtained in the step 1), wherein hydroxyl on the surface of TONFC and hydroxyl on the surface of CGF form hydrogen bonds during impregnation, so that the TONFC is adsorbed on the surface of the CGF.

Drying after impregnation to obtain the mixed fiber yarn absorbed with the nano material;

the mass ratio of the TONFC dry weight in the sol solution to the mixed yarn fabric is 0.1: 100-2: 100;

3) hot-press molding:

carrying out hot-press molding on the mixed fiber yarn obtained in the step 2) to obtain a thermoplastic composite material laminated plate toughened between TONFC layers and integrally toughened through phase change;

in the hot-press forming stage, the CGF and the TONFC respectively perform amidation reaction and esterification reaction with the PPR to form strong CGF/PPR and TONFC/PPR interfaces;

in the thermoplastic composite laminate, the TONFC is attached to the CGF surface in an array manner so as to be added into a composite fabric;

when the cracks are expanded in the interlayer area of the laminated plate after hot press forming, the rivet effect of the TONFC can deflect the propagation path of the cracks and induce the formation of rich fiber bridging and fiber bundle bridging, so that the aims of effectively preventing the crack expansion and obviously improving the interlayer fracture toughness can be achieved.

Preferably, in the step 1), the mass ratio of the softwood pulp to the oxidant is as follows: 1: 1-1: 20, wherein the molar ratio of TEMPO, NaBr and NaClO is as follows: 0.01-0.4: 0.1-3: 1-12.

Preferably, in the step 2), the mixed yarn fabric is twill 2/2 fabric, the CGF content in the mixed yarn fabric is 60 wt%, the CGF is modified by a silane coupling agent, the silane coupling agent comprises KH550, and the PPR in the mixed yarn is modified by maleic anhydride grafting.

Preferably, in the step 2), the pressure during the dipping treatment is 0.01-0.1 MPa, and the treatment time is 10-60 min.

Preferably, in the step 2), the drying temperature is 25-80 ℃, and the drying time is 3-8 h.

Preferably, in the step 3), the pressure of hot press molding is 0.1-1 MPa, the molding temperature is 165-250 ℃, and the heat preservation time is 1-10 min.

Preferably, in the step 3), the hot press molding is followed by cooling to room temperature, wherein the cooling rate is 1 to DEG C/min.

Preferably, in the step 3), an ester bond formed by the TONFC and the maleic anhydride in the thermoforming stage promotes the original α -phase portion in the matrix to be converted into the β -phase.

The invention also provides a high-layer discontinuous-crack tough thermoplastic composite laminated plate, which is prepared by the method.

The scheme of the invention has the following beneficial effects:

during crack propagation in the interlayer matrix-rich region, the crack is induced to deflect in the matrix by adding TONFC, the crack propagation path is prolonged, and a large number of fiber bridges and fiber bundle bridges are formed at the same time, so that the type I initial fracture toughness (G) and the propagation interlayer fracture toughness (G) of the thermoplastic composite laminated plate are remarkably improved_ICinit.And G_ICprop.) Respectively improved by 45.9 percent and 50.2 percent. In addition, the thermoplastic composite laminate also has more excellent energy dissipation upon low speed impact.

1. Compared with the existing melt blending mode with high cost and high energy consumption, the sol solution impregnation mode of the invention has the advantages of simple process and high efficiency, obviously reduces the manufacturing cost and is easy to realize industrial production from the economic point of view.

2. From the aspect of material properties, the glass fibers and the polypropylene fibers are arranged in a staggered mode, each glass fiber can be impregnated by the polypropylene, a stronger fiber/matrix interface is formed, and the high-end market application value is achieved.

3. From the aspect of process improvement performance, the invention opens up a new way for improving the interlaminar fracture toughness and also provides theoretical reference for improving the performance of other forms of mixed yarn composite materials.

Drawings

Figure 1 is a process flow diagram for the preparation of a laminate of the present invention.

Figure 2 is a static force versus displacement graph for a laminate in an embodiment of the invention.

FIG. 3 is a graph of interlaminar fracture toughness versus crack length for laminates of embodiments of the invention.

FIG. 4 is a graph of TONFC content and crack initiation and propagation fracture toughness (G) for laminates according to embodiments of the present invention_ICinit.And G_ICprop.) A histogram of the relationships of (1).

Figure 5 is an SEM image of the laminate interlaminar failure mechanism analysis in an embodiment of the invention.

Fig. 6 is an XRD diffraction pattern of the laminated plate layer in the example of the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.

Example 1

The invention provides a nano-cellulose toughened composite laminated board of mixed fiber yarn and a preparation method thereof, as shown in figure 1, the preparation method comprises the following steps:

1) preparing a TONFC sol solution:

mixing the total mass of TEMPO, NaBr and NaClO with softwood pulp in a mass ratio of 10:1 to prepare a solution, wherein the molar ratio of TEMPO to NaBr to NaClO is 0.024: 2.50: 7.13, carrying out an oxidation reaction at room temperature, wherein the C6 primary hydroxyl group is regioselectively converted into a carboxyl group in the NFC during the reaction, so that the TONFC is dispersed in the sol liquid in the form of single fibers through electrostatic repulsion; the solid content of the TONFC sol solution is 2.5 +/-0.5 wt%, the fiber length is more than or equal to 1 mu m, and the fiber diameter is 20-50 nm;

2) sol impregnation:

dipping the CGF/PPR mixed yarn fabric in the sol solution obtained in the step 1) for 30min under the pressure of 0.05 MPa; during impregnation, hydroxyl on the surface of the TONFC and hydroxyl on the surface of the CGF form hydrogen bonds to perform hydroxyl adsorption.

Drying for 6h at 50 ℃ after impregnation to obtain mixed fiber yarn;

the blended yarn fabric is twill 2/2 fabric, and the CGF content of the blended yarn fabric is 60 wt%. The CGF is modified by a KH550 silane coupling agent, and PPR in the mixed yarn is modified by maleic anhydride grafting.

The mass ratio of the TONFC dry weight in the sol solution to the mixed yarn fabric is 0.22: 100;

3) hot-press forming of the laminated plate:

carrying out hot-press molding on the mixed fiber yarn obtained in the step 2) at the temperature of 220 ℃ under 0.6MPa, and preserving heat for 6min at the temperature of 220 ℃. Then cooling to room temperature at a cooling rate of 40 ℃/min to obtain the TONFC interlayer toughened thermoplastic composite laminated board;

example 2

Example 2 is essentially the same as example 1, except that: in example 2, the mass ratio of the dry weight of the cellulose in the sol solution to the fabric was 0.44: 100;

example 3

Example 3 is essentially the same as example 1, except that: in example 3, the mass ratio of the dry weight of the cellulose in the sol solution to the fabric was 0.88: 100;

example 4

Example 4 is essentially the same as example 1, except that: in example 4, the mass ratio of the dry weight of the cellulose in the sol solution to the fabric was 1.76: 100;

and (3) testing mechanical properties: type I test

The test specimens were subjected to a Double Cantilever Beam (DCB) test according to ASTM D-5528 test method, with DCB test specimen dimensions of 150X 25.0X 8.0mm and an initial crack length of 50 mm. The DCB test was performed on a universal tester (MTS E45.105-B), and the interlaminar fracture toughness G of the test specimens was calculated by the Modified Beam Theory (MBT) and the following formula_ⅠC：

Wherein P is the applied load, the displacement of the loading point, b is the width of the specimen, a is the delamination length, and Δ is the crack length compensation value.

The control sample was a CGF/PPR blend yarn fabric sample without TONFC addition. The test results for the control sample and the laminates of examples 1-4 are shown in tables 1 and 2, respectively:

TABLE 1 force required for sample delamination in DCB test

Sample (I)	Force required for delamination (N)	Amplification relative to control sample
			Control sample	96.8	——
Example 1	160.5	65.8％
			Example 2	195.1	101.5％
Example 3	167.6	73.1％
			Example 4	92.4	——

In FIG. 2, a, b, c, d, e are static force-displacement curves for the control sample and the laminates of examples 1-4, respectively, in the DCB test. As can be seen from the static force-displacement curves, the force required to delaminate at the peak inflection points for the laminates of examples 1-4 was 160.5, 195.1, 167.6, and 92.4N, respectively, which are higher than the value for the control sample (i.e., 96.8N). By comparison, it was found that when the content of toffc was less than 0.88 wt/wt%, the force required for interlayer crack propagation was increased by 65.8%, 101.5%, and 73.1%, respectively, whereas when the mass ratio of toffc exceeded 0.88 wt/wt%, the force required for crack propagation was rapidly reduced. This shows that, on the one hand, the chemical reaction between the TONFC and the polypropylene matrix is favorable for promoting the formation of fiber bridging and fiber bundle bridging, and obviously improves the crack propagation resistance; on the other hand, too high content of the toffc results in unbalanced ratio of the surface group of the toffc to the maleic anhydride group, weakening the interface strength, and a weak interface becomes a source of crack initiation.

TABLE 2G of control and laminates of examples 1-4_ICinit.And G_ICprop.

Sample (I)	G_ICinit.(kJ/m²)	G_ICprop.(kJ/m²)
			Control sample	0.65	0.78
Example 2	1.25	1.57
			Example 3	0.95	1.17

As shown in FIGS. 3 and 4, as the TONFC content increased, the interlaminar fracture toughness (G) was initiated and extended_ICinitAnd G_ICprop.)G_ICThe initial and spread values generally increased and then decreased, and it is apparent that the laminates of example 2 (i.e., 0.44 wt/wt% TONFC) have significantly improved fracture delamination resistance, G_ICinit0.65kJ/m from control sample²To 1.25kJ/m of toughened laminate²The improvement is about 92.0 percent. G_ICprop.0.78kJ/m from control sample²Increased to 1.57kJ/m of toughened laminate²The improvement is about 101.7%. At 0.88 wt% TONFC (i.e., the laminate of example 3), a small increase in initial fracture toughness was observed, G_ICinit0.65kJ/m from control sample²To toughened laminates of 0.95kJ/m²Increased by about 45.9%; g_ICprop.0.78kJ/m from control sample²Added to 1.17kJ/m of toughened laminated plate²The improvement is about 50.2%. The toughening mechanism of tomfc is due to its creation of anchoring zones within the polypropylene matrix and improved perturbation to the crack front, limiting crack propagation and thus increasing energy absorption. In other words, the cracks of the filled composite are deflected and pinned by the reinforcing barrier (i.e., toffc) to absorb more energy and thus possess higher fracture toughness.

SEM images of the fracture surface after DCB testing of the sample are shown in fig. 5. In fig. 5, (a), (b), (c), (d), and (e) are SEM images of the fracture surfaces of the control sample and the laminates of examples 1 to 4, respectively, and (a1), (b1), (c1), (d1), and (e1) are SEM images of the fiber surfaces at A, B, C, D, E in (a), (b), (c), (d), and (e), respectively, which shows that the interface between the fibers of the control sample and the PP matrix is debonded, and the debonded fibers can be clearly observed. Interlaminar fracture of the laminates of examples 1-4 was controlled by fiber bridging, debonding, and pulling of toffc, resulting in two failure modes: (1) pinning and crack tips diverge at the toffc interface; (2) shear failure of the matrix. This indicates that the strengthening effect of TONFC in the interlaminar region of adjacent plies results in a strong bond at the interface, advantageously increasing fracture toughness.

Meanwhile, the beta-phase advantageous for improving toughness occurred in examples 1, 2, 3, and 4, as compared to the control sample (as shown in fig. 6).

While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A preparation method of a nano-cellulose toughened mixed fiber yarn composite material laminated plate is characterized by comprising the following steps:

1) preparation of oxidized nanofibrillated cellulose sol solution:

preparing oxidized nanofibrillated cellulose sol solution by taking softwood pulp as a raw material and 2,2,6, 6-tetramethylpiperidine-1-nitric oxide, sodium bromide and sodium hypochlorite as oxidants;

2) sol impregnation:

impregnating the continuous glass fiber/random copolymerization polypropylene fiber mixed yarn fabric with the sol solution obtained in the step 1), and then drying to obtain mixed yarn adsorbed with the nano material;

the mass ratio of the dry weight of the oxidized nanofibrillated cellulose in the sol solution to the mixed yarn fabric is 0.1: 100-2: 100;

3) hot-press molding:

carrying out hot-press molding on the mixed fiber yarn obtained in the step 2) to obtain the composite material laminated plate toughened by the oxidized nano fibrillated cellulose interlamination and integrally toughened by phase change.

2. The preparation method according to claim 1, wherein in the step 1), the mass ratio of softwood pulp to oxidant is as follows: 1: 1-1: 20, wherein the molar ratio of 2,2,6, 6-tetramethylpiperidine-1-nitrogen oxide to sodium bromide to sodium hypochlorite is as follows: 0.01-0.4: 0.1-3: 1-12.

3. The preparation method of claim 1, wherein in the step 2), the blended yarn fabric is twill 2/2 fabric, the content of glass fiber in the blended yarn fabric is 60 wt%, the glass fiber is modified by a silane coupling agent, and random copolymer polypropylene in the blended yarn is modified by maleic anhydride grafting.

4. The method according to claim 1, wherein in the step 2), the pressure during the dipping treatment is 0.01 to 0.1MPa, and the treatment time is 10 to 60 min.

5. The preparation method according to claim 1, wherein in the step 2), the drying temperature is 25-80 ℃ and the drying time is 3-8 h.

6. The preparation method according to claim 1, wherein in the step 3), the pressure of hot press forming is 0.1-1 MPa, the forming temperature is 165-250 ℃, and the holding time is 1-10 min.

7. The preparation method according to claim 1, wherein in the step 3), the hot-press forming is followed by cooling to room temperature, wherein the cooling rate is 1-60 ℃/min.

8. The preparation method according to claim 1, wherein in the step 3), the phase transition bulk toughening means that the alpha phase part in the matrix is induced to be converted into the beta phase.

9. A high nanocellulose toughened hybrid fiber yarn composite laminate prepared by the method of any one of claims 1 to 8.