MX2011008552A - Process and product obtained from a sawdust and recycled polymer using wood processing wastes. - Google Patents

Abstract

A composite product has been developed which main components are the solid residues of wood and polymeric resin, preferably PET. The composite material may or may not comprise a fire retardant as additive. First, the sawdust is verified and dried. Both sawdust and polymer, and the flame retardant if used, are weighted in suitable amounts according to the characteristics of the desired final product. The components are mixed together at high temperatures by twin-screw extrusion for obtaining a homogeneous mixture. The final melted mixture is poured into a hot mould to be compressed in a press for finally obtaining the product. The product of the present invention may be used as plastic tile for roofs, wood and chipboard substitute, plastic floors, vehicle boards, fence posts, automotive plastic accessories, road reflecting signals, road plastic speed bumps, etc., depending on the physical properties of the article to be manufactured.

Description

PROCESS AND PRODUCT OBTAINED FROM A RECYCLED ASERRIN AND POLYMER MIXTURE USING WASTE FROM THE PROCESSING OF WOOD DESCRIPTION FIELD OF THE INVENTION The present invention relates to the development of a process and the elaboration of a product, resulting therefrom, which uses as waste raw material wood processing, particularly that generated during the sanding of wood surfaces, known as the dust of sawdust. Sawdust is mixed with a recycled thermoplastic polymer resin resulting in a rigid material with specific properties. The composite material improves the characteristics of flexural and tensile strength when compared to the same virgin polymer resin. This material can be used as a raw material in the production of rigid plastic parts whose use is, among others: pallets, floor, substitute for compressed wood, and any other item that requires the physical characteristics offered.

BACKGROUND In Mexico, as in other countries of the world, concern has been accentuated by the reuse of plastic waste, which due to its non-biodegradable characteristics and the high volume in which they are produced, constitute a serious problem for the environment. One of the sectors that contribute significantly to the generation of waste in Mexico is the one corresponding to the chemical and petrochemical sector with 40% of the total annual volume generated from plastic waste.

In the plastics industry, one of the main waste generated is PET bottles, polyethylene terephthalate (or polyethylene terephthalate), in chemical jargon. Around 3 million tons of post-consumer plastics are generated per year, of which only 21% is recycled [Mónica Conde (2010), Principle and end of the raw material, Ambiente Plástico No. 41, p48]. One of the plastics with greater consumption is the PET used in the manufacture of bottles for beverages, both in the soft drink industry and bottled water, with a consumption of 460 thousand tons per year. In most cases, PET waste ends up in the municipal sanitary landfill or in uncontrolled sites, constituting a potential problem of air and soil contamination. The rate of capture of PET bottle is almost 20% of national consumption [Ing. Eduardo Martínez Hernández (2011): Press release (bulletin No. 6), ANIPAC, http://www.anipac.com.mx/anipac06/descargas/BOLETIN6.pdf]. Its low rate of collection and consequent recycling involves multiple factors such as the non-separation of urban solid waste (MSW) in homes, poor systems collection that does not classify the RSU, lack of a legislative framework that promotes and encourages recycling [Horacio Villalón Mendoza (November, 2010). Situation of urban solid waste separation in Santiago, Nuevo León, UANL. Available at: http://eprints.uanl.mx/291/1/residuossolidos.pdfl. and finally, the low cost paid per kilogram of PET to the collectors [Elvira Schwanse and Andrés Chaves (2010). Obstacles and incentives for the recycling of PET, Plastic Environment, No 41]. Recycled plastic beginning and end].

Another notable factor is that 65% of PET captured is sent to China and the rest is recycled in Mexico. The recycling rate is very low due to the absence of industries that demand recycled resins [Ing. Eduardo Martínez Hernández (2011), Bulletin No. 6, ANIPAC. http://www.anipac.com.mx/anipac06/descargas/BOLETIN6.pdf.]. It can be added that the technologies for recycling imply a high investment margin and due to the high degree of contamination that presents the PET collected the cost to recycle it increases. For this reason it has been important to develop an appropriate technology that allows to take advantage of such waste in viable and profitable production processes, thus contributing not only to the solution of this important problem of environmental pollution, but also giving an added value to the solid waste of bottles.

The main components of the new material are waste from water bottles and soft drinks. Historically, research into the potential use of PET waste as a polymer matrix is small. A material The compound that uses PET is the one developed in the patent 5339804 (1994) where a material with the appearance of wood is obtained, but it does not use sawdust as a component. A PET-sawdust compound can also be found, which differs from the present invention in that it does not use coupling agent and therefore its properties are lower (RS P20060223 A), a PMMA / sawdust compound with plaster filling (CN 101531799) , a plastic-wood decorative paper (CN 101519861 A), a PET-rice husk composite material (CN 1709970 A), plastic doors manufactured with wood whose process is by compression molding and much more complicated than the one presented here (KR 20030092661 A), as well as a PET-wood composite material that includes the use of inorganic fillers and blowing agents (WO 2005033204).

In this invention the sawdust is mixed with the polymer resin. The properties of the final article depend to a large extent on the recycled PET used due to the intrinsic properties (viscosity) of the resin. Various types of resins can be used, whose characteristics also define the conditions that must be selected for optimum processing and processing of the material. Not only redoxed resins can be used in the mixture, but also virgin polymers, which results in a cheapening of the articles to be produced, since there is a waste raw material in the two main components of the product elaborated in the present invention. .

DETAILED DESCRIPTION OF THE INVENTION The invention relates to the preparation of a composite material and a method that allows the reuse of waste from the plastics industry, with a consequent reduction in the volumes of plastic waste that impact the environment and also create value-added articles to from this waste.

The capacity, quantity of processed product, and its characteristics can have different variants. This variation will be a function of the infrastructure of the production plant, that is, it can be adjusted by properly handling the percentages and the process control variables: temperature, extrusion speed, concentration or percentage of the wood waste with respect to the polymer resin, etc. The suggested range of wood concentrations in the composite material can vary between 5% and 40% of the total weight of the mixture, preferably from 20% to 30%, and that of the polymeric resin, which preferably must be PET (Terephthalate polyethylene) virgin and / or recycled, but polyethylene, polypropylene, polystyrene, polyamides, acryl-butyl-styrene can be used, and can be from 60% to 95% of the total weight of the mixture. Thus, the description of the process to follow for the elaboration of the composite material is the following: 1 - . 1 - Verification of wood waste in order to retain or separate foreign agents, such as metals.

Drying the wood residue by means of suitable equipment up to a humidity of less than 5%, to avoid the formation of water vapor bubbles in the extrusion chamber.

Crushed by means of a suitable equipment that allows to obtain particles between mesh of 10 and 35 (AST E11), approximately.

Weighing of materials, sawdust and polymeric resin (pellet or ojuela), in addition to the plastic-sawdust compatibilizing additives, in the proportions required by the desired properties of the final product (within the range of proportions already mentioned above).

Addition of flame retardant (optional), in which case it is suggested to add it between 2.5% and 15% of the total weight of the mixture, preferably MgO. Homogenization of the mixture of materials (resin, powder, additives) by the method considered convenient.

Gradual addition of the mixture of components to the feed hopper where the extrusion chamber should be at temperatures in a range of 240 ° C to 265 ° C. The minimum limit value of this interval must be greater than the melting temperature of the resin used. The maximum value is a function of the combustion characteristics of the sawdust and the residence time of the material inside the extrusion mixing chamber. The operation can be carried out from laboratory level to industrial level.

The amount of added sawdust can vary between 5% and 40% by weight in relation to the total weight of the processed mixture. The extrusion speed can vary between 20 and 90 rpm, depending on the maximum torque value permissible in the equipment and its operating characteristics. For reasons of productivity and quality control, this stage should be as fast as possible, a maximum of 60 seconds of residence time is suggested.

. The removal of the melt composite from the extrusion mixing chamber is carried out naturally by the process itself through the extrusion die. 10. Transfer the mixture in small batches to a mold at a pre-temperature between 240 ° C and 265 ° C and sprayed with release agent, this being preferably a silicone base. 11. Compression in a molding equipment at temperatures between 240 ° C and 265 ° C at 24,000 Ib of compression force for a maximum time of 1 min. The mold provides the shape of the article to be made.

The quantities to be used, as well as the ranges of the operation variables that can be suggested in the process, are shown in Table 1. The variables are adjusted and any range is taken depending on the possibilities of plant equipment and the type of resin . For example, PET resins (polyethylene terephthalate) were used.

The material object of this invention can be useful as plastic roofing tiles, wood and compressed wood substitute, plastic floors, car boards, fence posts, automotive plastic accessories, road ghosts, road plastic stops, plastic road buoys, etc. ., depending on the physical properties of the item to be processed. To illustrate the product resulting from the aforementioned process, such as a plastic floor, we have that the composite materials with a resin of virgin PET of high and low intrinsic viscosity, were analyzed under stress and bending tests (load to yield) for the same thickness of plate with two types of compatibilizing additives, high density polyethylene and polypropylene, both maleated, as well as two particle sizes, 18 mesh and 10 mesh, and two wood concentrations, 10 and 20%. The results are shown in the Table: Table 2. Tension and bending stresses for different formulations of composite material.

Claims (3)

CLAIMS Having sufficiently described our invention, which we consider as a novelty and therefore claim as our exclusive property contained in the following clauses:

1. - A process for preparing new composite materials from the waste of wood processing and a virgin or recycled polymer resin, such as polyethylene, polypropylene, polystyrene, polyamides, acryl-butyl-styrene, polymethylmethacrylate; or, preferably, polyethylene terephthalate (PET) and comprising the following steps: a) verification and drying of the wood particles up to a humidity of less than 5%, b) grinding of the wood particle up to a mesh size between 10 and 35 (ASTM E11) c) heating of double-screw extrusion chamber up to temperatures between 240 ° C and 265 ° C, and whose mixing rotors must work in a range of rotation speeds between 20 rpm and 90 rpm, d ) gradual addition of the mixture resin (s) - sawdust previously homogenized inside the feeding chamber (hopper) of the twin screw extruder with a residence time not greater than 60 seconds, e) removal and emptying of the molten mixture from the extrusion chamber to a pre-heated mold (240-265 ° C) and mold release, this being preferably silicone-based, f) formation of the product by means of compression molding, for a maximum of 1 minute, at temperatures between e 240 ° C and 265 ° C, and at a compression force between 20,000 and 30,000 Ib, preferably 24,000 Ib; the mold provides the shape of the finished solidified product.

2 - . 2 - Composite material that consists of waste of wood processing and virgin or recycled polymer resin, having as optional the use of flame retardant, obtainable by the process described in clause 1, characterized because: a) the waste of wood presents a weight of between 5% to 40% of the total weight of the composite mixture, b) the wood waste has a particle size between 10 mesh and 35 mesh (ASTM D11) c) polymer resin, polyethylene, polypropylene, polystyrene , polyamides, acryl-butyl-styrene, polymethylmethacrylate, but preferably polyethylene terephthalate, has a weight of between 60% to 95% of the total weight of the composite mixture and can be virgin or recycled, and d) the flame retardant , if it is used, preferably MgO, it presents a weight between 2.5% and 15% of the total weight of the composite mixture.

3. - Use of the composite material claimed in clause 2 and obtained by the process of claim 1 for the production of plastic roofing tiles, wood and compressed wood substitute, wall tile, plastic floors, car boards, fence posts, automotive plastic accessories, highway ghosts, plastic road bumpers, plastic road buoys.