Multilayered composite material using nanofibrillated cellulose and thermoplastic matrix polymer

Abstract

The present invention relates to a multi-layered composite material manufactured by thermocompressing a multi-layered sheet, comprising: a first sheet layer formed from a solution containing nanofibrillated cellulose and a first thermoplastic matrix polymer; and a second sheet layer formed from a solution containing a second thermoplastic matrix polymer. The multi-layered composite material of the present invention has the high strength and high elastic modulus.

Claims

1. A method of manufacturing a multi-layered composite material having at least one of a first sheet layer comprising a nanofibrillated cellulose and a first thermoplastic polyamide fiber in a weight ratio of 3:7 to 4:6 and a least one of a second sheet layer comprising a second thermoplastic polyamide fiber without nanofibrillated cellulose are alternately laminated by thermocompressing, wherein the method comprises: a first step of preparing the first sheet layer, the first step comprising 1) forming a nanofibrillated cellulose suspension by mixing the nanofibrillated cellulose and the first thermoplastic polyamide fiber, wherein the diameter of the nanofibrillated cellulose ranges from 10 nm to 110 nm and the first thermoplastic polyamide fiber has a length ranging from 0.1 mm to 3.0 mm, and 2) drying and compressing the nanofibrillated cellulose suspension to form the first sheet layer having pores; a second step comprising preparing the second sheet layer wherein the second sheet layer is a hot-melt web or a meltblown nonwoven fabric comprising the second thermoplastic polyamide fiber without nanofibrillated cellulose; a third step comprising alternately laminating 1) at least one first sheet layer comprising the nanofibrillated cellulose and the first thermoplastic polyamide fiber in a weight ratio of 3:7 to 4:6; and 2) at least one second sheet layer comprising the second thermoplastic polyamide fiber without the nanofibrillated cellulose to form alternately laminated multi-layers; and a fourth step comprising hot-melting the alternately laminated multi-layers by applying a pressure to the alternately laminated multi-layers at a temperature below the degradation temperature of nanofibrillated cellulose, wherein the second thermoplastic polyamide fiber flows into the pores of the first sheet layer to form a melt-connected polymer matrix between the first thermoplastic polyamide fiber, the second thermoplastic polyamide fiber and the nanofibrillated cellulose of the first sheet layer.

2. The method of claim 1, wherein the first thermoplastic polyamide fiber and the second thermoplastic polyamide fiber are the same or different polyamides having compatibility with nanofibrillated cellulose.

3. The method of claim 1, wherein the temperature in the fourth step is in the range of 100 C. to 200 C. when the second layer sheet is a hot-melt web, or in the range of 170 C. to 270 C. when the second layer sheet is a meltblown nonwoven fabric and wherein the applied pressure is in the range of 4 MPa to 110 MPa.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A and 1B show the multi-layered composite materials formed by laminating or thermocompressing the sheet consisting of nanofibrillated cellulose and meltblown nonwoven fabric, which is an adhesive layer, by a conventional method, and FIG. 1C illustrates a multi-layered composite material formed by thermocompressing of the NC/first thermoplastic matrix polymer and the second thermoplastic matrix polymer, which is an adhesive layer, according to an exemplary embodiment of the present invention.

(2) FIG. 2 shows a process chart of manufacturing a multi-layered composite material in the form of a sheet using nanofibrillated cellulose and thermoplastic matrix polymer by the wet web formation and drying processes.

(3) FIG. 3 shows a structure of a multi-layered composite material consisting of an NC/PA composite material and an adhesive layer (a hot-melt web, a meltblown nonwoven fabric, and a film), according to an exemplary embodiment of the present invention.

(4) FIG. 4 shows the scanning electron microscope images of the surfaces and cross-sections of an NC/PA multi-layered composite material of Example 2.

(5) FIG. 5 shows a graph illustrating the tensile modulus of an NC/PA multi-layered composite material according to an adhesive layer, a thermocompressing pressure, and an NC content.

(6) FIG. 6 shows a graph illustrating the flexural modulus of an NC/PA multi-layered composite material according to an adhesive layer, a thermocompressing pressure, and an NC content.

(7) FIG. 7 shows a graph illustrating the fracture fatigue properties of the composite materials of PA66 sheet, NC/PA6, and NC/PA66.

(8) FIG. 8 shows a graph illustrating the tensile strength and tensile modulus of the composite materials of NC/PA/NY and NC/PA/AB.

(9) FIG. 9 shows a graph illustrating the flexural strength and flexural modulus of the composite materials of NC/PA/NY and NC/PA/AB.

(10) FIG. 10 shows a graph illustrating the impact strength of the composite materials of NC/PA/NY and NC/PA/AB.

DETAILED DESCRIPTION OF THE INVENTION

(11) Hereinafter, the present invention will be described in detail with reference to the following Examples. However, the Examples of the present invention may be embodied in many different forms and these Examples should not be construed as limiting the scope of the present invention.

Example 1: Preparation of a Composite Material Containing Nanofibrillated Cellulose and Thermoplastic Matrix Polymer

(12) First, a pulp dispersion was prepared by dispersing a hardwood pulp of a fiber length of 1.0 mm into water, followed by dissociation via mechanical refining in a pulper for 30 minutes. A pulp dispersion of a solid concentration of 0.2 wt % was prepared, stirred for 30 minutes, and then fibrillated by a homogenizer.

(13) The pulp dispersion was passed through three nozzles of different size, installed in a high pressure homogenizer, in a sequential order of nozzle diameter, as follows: 1) 5 times: nozzle diameter 250 m, pressure 70 MPa, 2) 5 times: nozzle diameter 200 m, pressure 240 MPa, and 3) 5 times: nozzle diameter 150 m, pressure 310 MPa. The cellulose dispersion was passed 5 times per nozzle (i.e., a total of 15 times of the homogenizing process), and a nano sized fibrillated cellulose (nanofibrillated cellulose, NC) suspension was thereby prepared.

(14) The thus-prepared NC suspension and two kinds of polyamide (PA) fibers (PA6 or PA66) were mixed at a weight ratio of solid content of about 4:6, and the NC/PA composite material was prepared in the form of a sheet as illustrated in FIG. 2 by the wet web formation and drying processes. In particular, the length of the PA fiber used was 1.0 mm. The NC/PA6 sheet was prepared by a wet web formation process using 1,000 gradation stainless steel screen mesh, and dried under the conditions of 3.4 MPa pressure and at 80 C. for 2 hours in a heating press, and kept in an oven at the same temperature for 24 hours for further drying. To give an adhesive force, thus-dried NC/PA6 sheet was passed through a roll calendar at 210 C. under the pressure of 4.8 MPa at a speed of 0.5 m/min.

Example 2: Preparation of a Multi-Layered Composite Material Using a Composite Material Containing Nanofibrillated Cellulose and Thermoplastic Matrix Polymer

(15) For the preparation of a multi-layered composite material, as illustrated in FIG. 3, a PA6 hot-melt web, a meltblown nonwoven fabric, or a film was laminated between the NC/PA6 sheet layers prepared in Example 1, with a structure of 1 to 5 layers. In particular, the weight of the PA6 hot-melt web, the meltblown nonwoven fabric, and the film used were 17 g/m.sup.2, 100 g/m.sup.2 and 175 g/m.sup.2. Table 1 below represents the materials, thermocompressing conditions, NC contents, and sample names of the NC/PA multi-layered composite materials prepared in 1 to 5 layers. The surfaces and cross-sections of the NC/PA multi-layered composite materials were analyzed via a scanning electron microscope (SEM) (SU8000, Hitachi, Japan), and the results are shown in FIG. 4.

(16) TABLE-US-00001 TABLE 1 Matrix or NC Total Adhesive Thermocompressing No. of Content Thickness Sample Layer Conditions Layers (wt %) (m) Name 1 40.0 40 N1 PA hot- 150 C./60 sec 2 38.0 160 L2 melt web 3 37.4 280 L3 4 37.1 400 L4 5 37.0 490 L5 PA a 210 C. to 2 34.7 260 M2 meltblown 230 C./60 sec 3 33.3 420 M3 nonwoven 4 32.6 620 M4 fabric 5 32.2 830 M5 PA Film 210 C. to 2 38.0 170 F2 230 C./120 sec 3 37.4 290 F3 4 37.1 400 F4 5 37.0 540 F5 190 C./600 sec 3 40.0 100 S3 Preheating followed by 240 C./1,200 sec (87 MPa)

Experiment 1: Physical Properties of the NC/PA Composite Materials and the Multi-Layered Composite Material Prepared Using the Same

(17) (1) Tensile Modulus

(18) The tensile modulus of the composite materials was evaluated according to ASTM D638-03 using a universal testing machine (H100KS, Tinius Olsen, UK), and in particular, under the crosshead speed of 1.0 mm/min and a load cell of 2.5 kN.

(19) FIG. 5 illustrates the tensile modulus of the NC/PA multi-layered composite materials having different adhesive layers and NC contents, and being prepared under various thermocompressing pressures. That is, the tensile modulus of the NC/PA6 and NC/PA66 composite materials were measured, which were prepared by the method of Example 1 using PA6 or PA66 as polyamide fibers, and that of the multi-layered composite materials of Example 2, which were prepared using a PA hot-melt web (L), a PA meltblown nonwoven fabric (M), or a PA film (F) as the second thermoplastic matrix polymer layer (an adhesive layer or a second sheet layer). In FIG. 5, the NC/PA66-S composite materials were prepared by thermocompressing of three NC/PC66 sheets without using a matrix as in Example 2.

(20) Although the tensile modulus of PA66 sheet was 0.8 MPa, the tensile modulus of NC/PA6 and NC/PA66 composite materials was shown to be in the range of 1 MPa to 2 MPa and 3 MPa to 12 MPa according to NC contents. The tensile modulus of the NC/PA66 multi-layered composite material was higher than that of the NC/PA6 composite material, and the tensile modulus of the NC/PA6 composite material increased as the NC content increased. Additionally, the NC/PA multi-layered composite material subjected to thermocompressing at a pressure of 87 MPa was shown to have a higher tensile modulus compared to the NC/PA multi-layered composite material subjected to thermocompressing at a pressure of 4.8 MPa.

(21) (2) Flexural Modulus

(22) The flexural modulus of composite materials was evaluated according to ASTM D790-03 under the same conditions as in the evaluation of tensile modulus.

(23) FIG. 6 illustrates the flexural modulus of the NC/PA multi-layered composite materials having different adhesive layers, NC contents, and being prepared under different thermocompressing pressure. The NC/PA66-S composite material subjected to thermocompressing at a pressure of 87 MPa was shown to have a higher flexural modulus than all of the other materials. Further, NC/PA multi-layered composite materials using a PA meltblown nonwoven fabric as an adhesive layer, even with its low NC content, had a flexural modulus similar to those of the NC/PA multi-layered composite materials using a PA hot-melt web and a PA film as an adhesive layer. Namely, when the same NC content and the same thermocompressing pressure were applied, the NC/PA multi-layered composite materials using the PA meltblown nonwoven fabric as an adhesive layer were shown to have a higher flexural modulus than the NC/PA multi-layered composite materials using the PA hot-melt web or PA-film as an adhesive layer. The NC/PA66 multi-layered composite material was shown to have a higher flexural modulus than the NC/PA6 multi-layered composite material in all kinds of the adhesive layer.

(24) (3) Fracture Properties

(25) The fracture properties of the NC/PA composite material were evaluated according to ASTM D671-71 using an electrodynamic test system (Acumen 1, MTS system, USA), the load cell used was 3 kN, and the test was performed at a frequency of 20 Hz for 10.sup.6 cycles.

(26) FIG. 7 illustrates the fracture properties of PA66 sheet, and NC/PA6 and NC/PA66 composite materials. When experiments were performed repeatedly using a load cell of 3 kN at 20 Hz for 10.sup.6 cycles, it was confirmed that the reduction of fracture stress in the NC/PA66 composite material was smaller compared to those of the NC/PA6 composite material and the PA66 sheet. These results mean that the reinforcing effect of NC increases the service life of the NC/PA composite material. Additionally, the initial fracture stress value of NC/PA composite material was shown to be higher than that of the PA66 sheet due to the reinforcing effect of NC.

(27) Accordingly, it was confirmed that an NC/PA composite material with increased tensile modulus, flexural modulus, and service life can be prepared using the NC as a reinforcing material for PA.

Experiment 2: Physical Properties of a Multi-Layered Composite Material Comprising NC/PA Composite Materials and a Thermoplastic Panel

(28) The method of preparing the NC with a homogenizer under high pressure and preparing the NC/PA sheets was the same as described in Example 1, and illustrated in FIG. 2. The thus-prepared NC/PA sheet was adhered to a polyamide (PA) panel (sample code: NY) and an acrylonitrile butadiene styrene (ABS) panel (sample code: AB), respectively, and thereby NC/PA/NY and NC/PA/AB composite materials were prepared. For the preparation of the NC/PA/NY and NC/PA/AB composite materials by thermocompressing between the NC/PA sheet and NY, or between the NC/PA sheet and AB, a PA6 hot-melt web (sample code: L, 17 g/m.sup.2), a meltblown nonwoven fabric (sample code: M, 100 g/m.sup.2), and a film (sample code: F, 175 g/m.sup.2) were used as adhesive layers.

(29) The thus-prepared NC/PA/NY and NC/PA/AB composite materials, a single NY panel (sample code: NY-N), and a single AB panel (sample code: AB-N), both without attaching the NC/PA sheet thereto, and an NC/PA thermocompressed sheet without the adhesive layer (sample code: S) were compared by their tensile characteristics, flexural characteristics, fracture properties, and impact characteristics.

(30) In the preparation of the multi-layered composite materials, the thermocompressing between the composite materials and the adhesive layer for the samples of NY-S, NY-F, and NY-M was performed under the conditions of 210 C./40 seconds, and for the samples of NY-L and AB-L the thermocompressing was performed under the conditions of 130 C./60 seconds.

(31) (1) Tensile Strength and Tensile Modulus

(32) The tensile modulus of the NC/PA/NY and NC/PA/AB composite materials was evaluated according to ASTM D638-03 using a universal strength testing machine (H100KS, Tinius Olsen, UK), under the speed of 1.0 mm/min and a load cell of 50 kN.

(33) FIG. 8 illustrates the tensile strength and tensile modulus of the NC/PA/NY and NC/PA/AB composite materials. The tensile strength and tensile modulus of the composite materials were increased by attaching an NC/PA sheet to the NY or AB panel. The tensile strength and tensile modulus of the NC/PA/NY composite material were increased compared to the NY panel by a maximum of 158% and 126%, respectively. Additionally, the tensile strength and tensile modulus of the NC/PA/AB composite material were increased compared to the AB panel by a maximum of 130% and 126%, respectively. In particular, it was confirmed that the tensile modulus of the NY panel subjected to thermocompressing using the PA hot-melt web as an adhesive layer showed a significant increase compared to the composite material, which was attached by the PA film or the PA meltblown nonwoven fabric.

(34) (2) Flexural Strength and Flexural Modulus

(35) The flexural modulus of the prepared composite material was evaluated according to ASTM D790-03, under the same conditions of Experimental 1.

(36) FIG. 9 illustrates the flexural strength and flexural modulus of the NC/PA/NY and NC/PA/AB composite materials. The flexural strength and flexural modulus of the composite materials were increased by attaching an NC/PA sheet to the NY or AB panel, and in particular, the flexural strength and flexural modulus of the NC/PA/AB composite material were increased compared to the AB panel by 292% and 160%, respectively.

(37) (3) Fracture Fatigue Properties

(38) The fracture properties of the NC/PA/NY and NC/PA/AB composite materials were evaluated according to ASTM D671-71 using an electrodynamic test system (Acumen 1, MTS system, USA). The load cell used was 3 kN and the test was performed at a frequency of 10 Hz for 10.sup.6 cycles.

(39) The fracture fatigue properties of the NC/PA/NY and NC/PA/AB composite materials are illustrated in Table 2 below. When tests were performed for 10.sup.6 cycles with a strength of 70%, 50%, and 30% of the maximum flexural force, the fracture cycle of the AB-L sample, in which NC/PA/AB was adhered with a PA hot-melt film, was shown to be highest with a strength of 70%. With a strength of 50%, the NY-F sample, in which the NC/PA/NY was attached with a PA film, showed the highest increase of the maximum fracture cycle. Additionally, with a strength of 30%, all samples passed the 10.sup.6 cycle test. It was confirmed that the number of the fracture cycles significantly increased in all case of the NC/PA/NY and NC/PA/AB composite materials regardless of the kinds of the adhesive.

(40) TABLE-US-00002 TABLE 2 Max. flexural force Sample Number of cycles codes 70% 50% 30% NY-N 19 559 Pass NY-S 35 704 Pass NY-L 25 1739 Pass NY-F 1796 29823 Pass NY-M 19 844 pass AB-N 2798 43892 Pass AB-L 4443 78627 Pass
(4) Impact Characteristics

(41) The impact characteristics of the prepared composite materials were tested according to ASTM D 5420 using the Gardner impact test method (falling weight), which was performed by dropping a ball having a diameter of 50 mm from a height of 1,520 mm by a steel ball drop test machine.

(42) FIG. 10 illustrates the impact characteristics of the NC/PA/NY and NC/PA/AB composite materials. The NC/PA/NY composite material showed an excellent impact absorbing characteristic compared to the NC/PA/AB composite material, and it was confirmed that impact characteristics are improved by the adhesion of the NC/PA sheet.

(43) Accordingly, it was confirmed that tensile, flexural, fracture, and impact characteristics can be improved by attaching the NC/PA sheet to the NY and AB panels.