RU2127664C1 - Composite with cellulose fillers - Google Patents

Abstract

FIELD: composites. SUBSTANCE: invention relates to composites with cellulose filler and polyethylene-based thermoplastic binder designed for manufacturing piece products such as facing slabs and continuous products such as floor moldings, stair-case railing, rod stock for fabrication of furniture parts, packages, and so on. To increase homogeneity, mechanical strength, and water resistance, material is manufactured on the basis of preliminarily crushed, homogenized, and granulated polyethylene-laminated paper waste and contains cellulose filler and polyethylene-based thermoplastic binder at volume ratio 1:(0.4-1.2). Up to 1/3 of binder volume can be polystyrene or up to polypropylene. EFFECT: improved physico-mechanical characteristics. 3 cl, 2 tbl

Description

 The invention relates to the composition of polymer composite materials with cellulose filler and a thermoplastic binder based on polyethylene, which are intended for the manufacture of products such as tiles, plates, sheets and rods (including shaped profiles) for subsequent use in construction (especially cottages and outbuildings personal plots); preferably decorative and decoration furniture details; multi-turn packaging, etc.

The need for such materials is due to:
the need for resource conservation against the backdrop of a shortage of industrial wood for the production of industrial pulp and, in part, a shortage of primary thermoplastics, including polyolefins;
the need for disposal of packaging waste for food products and perfumery and other industries;
the need to use the production capacities of enterprises subjected to conversion.

 Taking into account the indicated areas of application, the requirements are imposed on composite materials for the highest possible moisture resistance and isotropy in mechanical properties at the lowest possible density and the requirement for suitability for processing into these products using standard equipment.

 Separate fulfillment of these requirements does not present significant difficulties.

 Indeed, composite materials based on primary polyethylene with additives of various disperse fillers are widely known, traditionally manufactured by mixing the ingredients in screw mixers (including direct processing of the resulting mixture into products of the required shapes by extrusion through profiled extrusion heads).

 For example, mixtures of polyethylene and mineral fillers (chalk, talc, mica, aerosil) are known with a concentration in the range of 10-30% by weight (see TU 6-05-1409-79 or Application of plastics: Handbook. - L .: Chemistry 1985, p. 19-21).

These materials have extremely low water absorption (less than 1%, usually less than 0.2%), acceptable strength and isotropic. However, these fillers have the form of dust with a developed specific surface. Therefore, even prolonged mixing in worm mixers does not ensure uniform wetting of all filler particles with a polyethylene melt, and their final concentration in these materials usually does not exceed 10% by volume. In addition, even at such low volume concentrations and at significant costs for mixing with polyethylene, the formation of mechanical conglomerates of fillers is possible, the strength of which is only an insignificant part of the strength of pure polyethylene. Further, the density of these fillers is significantly greater than 1000 kg / m ³ . Therefore, the density of composite materials also significantly exceeds 1000 kg / m ³ , which is acceptable, for example, in electrical engineering, but undesirable in construction and, especially, in the furniture industry. And finally, the use of binder partially degraded during the previous processing of secondary polyethylene is practically eliminated.

 For these reasons, for the disposal of waste from woodworking enterprises (sawdust and shavings), the pulp and paper industry (osprey) and enterprises using paper and cardboard for the manufacture of containers, they usually use more expensive than polyethylene, but allow the introduction of fillers up to 70-80% the volume of thermosetting oligomeric binders of the type of environmentally harmful phenol, urea and melamine formaldehyde resins (see, for example, Litvintseva GA, Pavlov VF and Medvedev ME Chemical materials used in the furniture industry and -. M .: Forest Industry, 1973, pp 220-223)..

 Accordingly, the problem of the energy and environmentally acceptable disposal of cellulose waste and thermoplastics remains formulated above. Of those known to the proposed technical essence, the closest is a composite material containing a cellulosic filler and a thermoplastic binder based on polyethylene (A.S. USSR 1419896). This material (see example 3 from the text of the description of the invention and examples 3 and 8 from table 1 therein) contains pure polyethylene (36% by weight) and veneer-crusher with an initial moisture content of 6-8% (rest) as a thermoplastic binder.

Since the indicated filler has a rather high humidity, the described composite material is obtained by jointly controlled feeding of the ingredients into a worm mixer, their preliminary mixing at a temperature of 130-150 ^o C and a screw speed of 18-40 min ^-1 with extrusion at the same temperature and pressure of 5-8 MPa for concurrent drying of the filler and achieving a residual moisture content of the composite material of 0.5-2%.

However, even with two-stage mixing and hard extrusion, the wet filler particles cannot effectively interact with the melt of hydrophobic polyethylene. Therefore, due to the weak adhesion of the binder to the surface irregularities and the blocking of the pores of the filler particles, the finished composite material is loose, delaminating at a break and unstable in a humid environment. Indeed, water absorption in 24 hours reaches 30% for the material extruded at 5 MPa and 130 ^o C, and for the material obtained at 150 ^o C and 8 MPa, water absorption is reduced to only 23%. In addition, satisfactory indicators of the mechanical strength of such a material are ensured only by pressing at high pressure, which leads to an excessive increase in its density, and the removal of excess moisture is achieved only by high-temperature drying and pressing of products, which is energetically disadvantageous and significantly worsens working conditions.

 Therefore, the invention is based on the task of refining the formulation to create from a cellulosic filler and a thermoplastic binder based on polyethylene a substantially more homogeneous, mechanically strong and water-resistant composite material.

 The problem is solved in that the composite material with a cellulose filler and a thermoplastic binder based on polyethylene according to the invention is made on the basis of pre-crushed, homogenized and granular waste laminated with polyethylene paper and contains cellulose filler and a thermoplastic binder based on polyethylene in a volume ratio of 1: (0, 4-1,2).

 Hereinafter, the term "polyethylene laminated paper" denotes packaging material in the form of paper or a half-carton with a layer of polyethylene at least on one of its sides.

 Since the basis of the proposed composite material is crushed waste of such packaging material and since the crushed semi-finished product is previously (that is, processed into the above products) homogenized and granulated, the filler particles in the material are almost completely moistened with a binder. Therefore, it is impossible to detect paper particles at the fracture of the samples of the proposed material during their visual examination, and the material as a whole, subject to the indicated ratios, turns out to be very homogeneous, isotropic in physical and mechanical properties and waterproof.

 The first additional difference is that up to a third of the volume of the thermoplastic binder is polystyrene. This allows you to effectively dispose of waste polystyrene processing, for example by injection molding, and to further increase the water resistance of the composite material according to the invention.

 The second additional difference is that up to half the volume of the thermoplastic binder is polypropylene, which allows, as in the previous case, to utilize the waste of this valuable polymer and increase the strength of the composite material according to the invention.

 Further, the invention is illustrated by a description of the starting materials, examples of the composition of the composite material, a description of the method of its manufacture and the results of physical and mechanical tests.

 For the composite materials according to the invention, the main raw material is waste laminated with polyethylene paper, obtained, for example, in the packaging of juices, dairy products, etc. using the Tetrapack technology. These wastes (scraps) contain cellulose and from 25 to 75% by volume of polyethylene (hereinafter - PE).

 The specific amount of PE in the waste should be determined before it is crushed and fed for mixing, either according to the technical conditions for the appropriate type of packaging material, or by chemical analytical methods well known to specialists.

 Since the waste products differ in the ratio of cellulose to PE, in case of a deficiency of one of the main ingredients, the required amount of the missing ingredient can be added in accordance with the specific formulation of the composite material. Light dry waste paper and mainly secondary (but without signs of thermal degradation) PE, injection polystyrene (hereinafter referred to as PS) or can be used to adjust the composition of each particular batch of waste to a specific formulation of a composite material with a fixed ratio of cellulose filler / binder based on PE polypropylene (hereinafter PP).

 Mentioned waste may also vary in color. Therefore, when the finished product must have a certain color, the trimmings of the laminated paper are pre-sorted by color and / or additives of suitable dyes or pigments are added.

 To justify the concentration limits of the components, experiments were conducted in which the volume ratio “cellulose filler / binder based on PE” corresponded to the examples given in table 1. Examples 1 through 5 specify the proposed material in its main form, that is, how the composition of cellulose and polyethylene, and from the 6th to the 9th - a complex binder. In examples 2, 3, 4, 6, 7, 8, and 9, the volume ratio corresponds to the declared limits, and in examples 1 and 5, goes beyond them.

 In the experiments, for the production of the specific composite materials indicated in Table 1, waste was used in the form of scraps of laminated PE packaging half-carton with an average PE content of 35% by volume.

 A method of manufacturing the proposed composite material in the General case is as follows.

 The waste is crushed to obtain a mixture of particles with sizes from 0.04 to 5, preferably less than 2 mm To correct the compositions according to the recipes from table 1, packaging paper is used, crushed to obtain particles with the dimensions indicated for the main material, and (usually secondary) granular PE, PS, and PP with an average grain size of from about 2 to about 5 mm.

The crushed waste directly or with additives of pure cellulose and / or binders selected in accordance with a specific formulation (and possibly with pigment or dye additives) is intensively processed in a worm mixer at a temperature of at least 130 ^o C (only when using PE), preferably 150 -170 ^o C (for PE and PS), or - for PE and PP - at 180-200 ^o C. The resulting substantially homogeneous mixture of cellulose and a binder based on polyethylene is extruded through the strand die head and pelletized to obtain particles with an average size and the length and diameter of 2 - 5 mm.

 These granules can be stored in bulk or in bags in a dry, unheated room for as long as necessary. The maximum shelf life in the experiments was 1 year.

 The granules are processed into the desired products using conventional extruders equipped with suitable extrusion heads or extrusion. At the same time, the choice of equipment and accessories is not difficult for specialists.

For the experiments for each of the formulations listed in Table 1, plates 3 and 5 mm thick were made by extrusion through slit heads, from which samples were then cut for physical and mechanical tests, including:
- to determine water absorption according to GOST 4650-80 - in the form of square plates with a side of 50 mm and a thickness of 3 mm;
- to determine the tensile strength according to GOST 11262-80 - in the form of plates with a thickness of 3 mm with a width of the middle part of 20 mm (two sets, in the first of which the samples were cut lengthwise, and in the second - across the sheet);
- to determine the tensile strength under static bending according to GOST 4648-71 - in the form of rectangular plates with a cross section of 20 x 5 mm and a length of 50 mm (also two sets);
- to determine the compressive strength according to GOST 25602-80 - in the form of plates with a thickness of 5 mm and an area of 10 x 10 mm.

For water absorption tests, distilled water was used, in which samples were soaked for 24 hours at a temperature of 20 ^° C. Water absorption was determined as a percentage as the ratio of the mass difference of each sample after testing and its initial mass to the initial mass multiplied by 100.

 The tensile strength was determined in MPa on a tensile testing machine RT 250M-2 with a constant loading speed of 1 m / min from beginning to end.

 The tensile strength at transverse static bending was determined in MPa on a testing machine of the RTM 250M-2 type at a loading speed of 40 mm / min to fracture.

 The compressive strength was determined in MPa at the bench of the UMI-1 model with additional equipment for fixing the samples.

 The test results are shown in table 2.

 As can be seen from table 2, the best physical and mechanical properties of the proposed composite material is in cases where the total content of the binder based on polyethylene is within the stated limits. Moreover, going beyond the lower boundary worsens all indicators, and going beyond the upper boundary, which means an increase in the consumption of the binder, does not give a noticeable change in strength, the indices of which reach "saturation" and even slightly deteriorate.

 When the amount of the binder based on polyethylene is lower than stated, it is not enough to reliably connect the particles of the cellulose filler, which increases water saturation especially noticeably, and with an excess of the binder, “cork” extrusion becomes liquid, in which the continuity of the extrudate is violated due to shear deformations due to an increase in the relaxation time of free polymer macromolecules.

Claims (3)

 1. A composite material with a cellulose filler and a thermoplastic binder based on polyethylene, characterized in that it is made on the basis of pre-crushed homogenized and granular waste laminated with polyethylene paper and contains cellulose filler and a thermoplastic binder based on polyethylene in a volume ratio of 1: (0.4 - 1,2).  2. The material according to claim 1, characterized in that up to a third of the volume of the thermoplastic binder is polystyrene.  3. The material according to claim 1, characterized in that up to half the volume of the thermoplastic binder is polypropylene.

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