RU2486213C1 - Method of enhancing mechanical properties of polymer nanocomposite material based on anisodiametrical filler - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of enhancing mechanical properties of a polymer nanocomposite material based on anisodiametrical filler. According to the method, the material is extruded and the obtained extrudate is pressed. After extrusion, the extrudate undergoes X-ray structure analysis to determine orientation of particles of the anisodiametrical filler relative the axis of the extrudate. Before pressing, the extrudate is placed in a press mould such that the axis of the principal direction of oriented flaky particles of the anisodiametrical filler coincides with the longitudinal axis of the press mould and, consequently, the obtained film.

EFFECT: invention increases strength of obtained articles.

5 cl, 2 tbl, 2 ex

Description

The invention relates to the field of obtaining products from polymeric nanocomposite materials with anisodiametric nanoscale fillers. The result of the invention is the creation of products from nanocomposite material of various thicknesses with high mechanical properties (see table 1, 2).

Composition: composites from LDPE in an amount of 80-99%, a layered nanofiller in an amount of 0.1-15%, technological additives (plasticizers, antioxidants, plasticizers) 0-4%, obtained by direct mixing in a melt at temperatures of 170-220 ° C followed by extrusion and pressing of films, from 0.18 mm to 4 mm thick, with preliminary orientation of the extrudate.

A known method for producing exfoliated polymer / clay nanocomposites by solid-phase shear grinding (US patent No. 7223359). According to this method, exfoliated nanocomposites of a given composition (with low degrees of filling) are obtained in two stages. In the first, a filler pre-modified with a surfactant - surfactant (to improve compatibility with the polymer), is mixed with the polymer melt. Then, the composition cooled below the melting temperature of the matrix is processed in a twin-screw extruder, during which, as a result of the application of large shear stresses, the layered silicate (clay) is separated into separate plates.

A known method for producing exfoliated polymer / clay nanocomposite (patent EP No. 1055570). In this method, the nanofiller — clay modified with a surfactant — a quaternary ammonium salt — is mixed with a carboxylic acid or sulfonic acid, and then in an extruder with a molten polymer under shear grinding. The amount of modified clay is 1-40% of the mass. from polymer.

The disadvantage of all known methods is the low tensile strength of the films obtained from these compositions.

The technical result of the invention is to obtain composites with tensile strength, increased compared with composites of the same composition and processing mode, but not passed this stage.

The technical result is achieved in that a method of increasing the mechanical properties of a polymer nanocomposite material based on an anisodiametric filler involves extruding and subsequently pressing the obtained extrudate to make a film, and after extrusion an X-ray diffraction analysis of the PCA of the extrudate is carried out to determine the orientation of the anisodiametric filler particles relative to the axis of the extrudate therein, before the extrudate is pressed into the mold so that the main axis The orientation of the flocculent particles of the anisodiametric filler coincided with the longitudinal axis of the mold and, accordingly, of the resulting film.

In the particular case of the implementation of the film of nanocomposite material is pressed with a thickness of not more than 0.7 mm

In another particular case of implementation, additional pressing of a stack of films with a thickness of not more than 0.7 mm each is carried out until an article with a total thickness of not more than 0.7 mm is obtained.

It is also possible that, to obtain thick films, all films with a thickness of not more than 0.7 mm are stacked randomly relative to the longitudinal axis of the mold.

A layered silicate modified with aliphatic quaternary ammonium salts dimethyldioctadecylammonium bromide or cetyltrimethylammonium bromide is used as a nanosized anisodiametric filler.

The essence of the method is as follows. When conducting mechanical tests, it is usually assumed that the principle of similarity is applicable to polymers. Since the main mechanical characteristics - stress and elongation - are relative values (assigned, respectively, to the initial cross section and length), they should be approximately the same for samples of the same composition having different geometric dimensions. Meanwhile, if we turn to practice, it becomes clear that the principle of similarity is often not fulfilled. The relationship between the size of polymer samples and their strength (scale factor) was studied in the works of G. M. Bartenev, the main results of which are summarized in the monograph [G. Bartenev Strength and fracture mechanism of polymers. M .: Chemistry, 1984]. It was found that with an increase in the thickness of the studied polymers, the strength distribution curve shifts to a region of lower values, which is due to the statistical nature of the strength (with an increase in the size of the polymer sample, the probability of containing dangerous defects increases).

Studies were performed on pure polymers. It is noted that the dependence of mechanical characteristics on the size of the samples can be based not only on the presence of defects, but also structural differences, but this issue has not been studied in detail.

This factor is especially important for filled systems with nanoscale fillers, since mechanical anisotropy in bulk samples is caused by different orientations of anisodiametric nanoparticles in the polymer matrix, although the influence of defects (which can also be filler particles) also remains strong. Using the X-ray diffraction method, it was shown that anisodiametric nanoparticles of layered silicates are textured differently when pressing products of various sizes. This is due to the different intensity of the polymer melt flow during the pressing of articles of various sizes. As a result of the organization of the flow of the polymer nanocomposite, planar texturing of the filler nanoparticles can be carried out, which results in a significant increase in the mechanical properties of the product.

The results obtained relate to the following:

1. The resulting composites have a 2-fold increased elastic modulus compared to pure PE, which underwent the same processing.

2. The use of orientation before pressing allows you to get products with tensile strength increased by 40-120%, deformation by 570% compared with composites of the same composition and processing mode, but did not pass this stage.

3. The application of the described method allows to improve the distribution of layered silicate in the obtained films. As a result, the filler in the form of flakes is located in the plane of the resulting film planarly.

4. The use of thin-film methods allows to obtain films with different orientations along the surface and in the deeper layers, allowing to obtain structures similar to laminated, without complicating the process.

The inventors found that when the main direction of the flakes of the filler is located at an angle to the longitudinal axis of the film, the mechanical properties of the polymer nanocomposite material deteriorate sharply.

The most important new technique in the claimed method is that the orientation of the flocculent filler is determined by X-ray diffraction, i.e. they are not selected at the stage of producing composites, but later they are oriented during molding.

EXAMPLE 1

The mechanical properties of samples of various thicknesses made by extruding extrudates for different directions of cutting the “blades” from the disk relative to the axis of the extrudate. The composition of the nanocomposite PE 107-2K is 85% by mass., Cloisite 20A is 15% by mass. (Cloisite 20A - Montmorillonite flocculent nanofiller treated with surfactants (modified)).

Table 1 Sample Thickness, mm The direction of cutting the “blades” from the disk relative to the axis of the extrudate Module E, MPa Yield strength σ _{pr. Tech} , MPa Strength δ _pr.pr , MPa Strain ε,% 0.7 Along 130 ± 1.8 8.2 ± 0.2 11.6 ± 0.9 500 ± 46 Perpendicular 140 ± 1.8 8.8 ± 0.01 12.0 ± 0.6 520 ± 36 2.0 Along 197 ± 35 8.5 ± 0.1 11.7 ± 0.8 460 ± 34 Perpendicular 157 ± 27 7.3 ± 0.1 7.5 ± 0.2 80 ± 68

The mechanical characteristics of a film 0.7 mm thick are the same for all directions of cutting samples. For samples 2.0 mm thick, the mechanical characteristics of the film with the direction of cutting along the axis of the extrudate are significantly higher than in the perpendicular direction.

EXAMPLE 2

The mechanical properties of the samples obtained from the nanocomposite composition PE 107-2K - 85 wt.%, Cloisite 20A - 15 wt.%, With a thickness of 2 mm or more, made by various methods.

table 2 2 mm thick specimen pressing conditions The direction of cutting the “blades” from the disk relative to the axis of the extrudate Module E, MPa Yield strength σ _{pr. Tech} , MPa Strength δ _pr.pr , MPa Strain ε,% Thick extrudate specimen Along 197 + 35 8.5 + 0.1 11.9 + 0.8 460 + 34 Perpendicular 157 + 27 7.3 + 0.1 7.5 + 0.2 80 + 68 By pressing a stack of films 0.7 mm thick Random 136 + 18 12.4 + 0.6 16.6 + 0.7 540 + 3

If the diameter of the extrudate and the thickness of the restrictive ring are approximately equal, the polymer flow is insignificant, and the orientation of the filler particles in the initial extrudates (along the extrusion axis) is largely preserved in the obtained plates. If the thickness of the ring is much smaller than the diameter of the extrudate, an intense polymer melt flow occurs during pressing. Upon receipt of a sample 2 mm thick by pressing a stack of films 0.7 mm thick, the yield strength, strength and deformation are higher for all cutting directions than for samples obtained from extrudates.

Claims (5)

1. A method of increasing the mechanical properties of a polymer nanocomposite material based on an anisodiametric filler, comprising extruding and then pressing the obtained extrudate to produce a film, and after extrusion, an X-ray diffraction analysis of the PCA of the extrudate is carried out to determine the orientation of the anisodiametric filler particles relative to the axis of the extrudate, and extrudate is placed in the extrudate before pressing the mold so that the axis of the main direction of orientation of the flocculent particles nizodiametricheskogo filler coincides with the longitudinal axis of the mold and, accordingly, the resulting film. 2. The method according to claim 1, characterized in that the film of nanocomposite material is pressed with a thickness of not more than 0.7 mm 3. The method according to claim 2, characterized in that they further compress the stack of films with a thickness of not more than 0.7 mm each to obtain an article with a total thickness of not more than 0.7 mm. 4. The method according to claim 3, characterized in that all the films with a thickness of not more than 0.7 mm are stacked randomly relative to the longitudinal axis of the mold. 5. The method according to any one of the preceding paragraphs, characterized in that a layered silicate modified with aliphatic quaternary ammonium salts - dimethyldioctadecylammonium bromide or cetyltrimethylammonium bromide is used as a nanoscale anisodiametric filler.