WO2005026244A1

WO2005026244A1 - Process for mechanical recycling of composite polymeric material

Info

Publication number: WO2005026244A1
Application number: PCT/SI2004/000026
Authority: WO
Inventors: Andrej Krzan
Original assignee: KOLPA PROIZVODNJA IN PREDELAVA PLASTICNIH MAS DD
Current assignee: KOLPA PROIZVODNJA IN PREDELAVA PLASTICNIH MAS DD
Priority date: 2003-09-12
Filing date: 2004-08-18
Publication date: 2005-03-24
Anticipated expiration: 2006-03-12
Also published as: SI21606A

Abstract

The invention relates to a process for mechanical treatment of composite material consisting of partially cross-linked polymethylmetacrylate, acrylonitrile-butadiene-styrene copolymer, unsaturated polyester resin and glass fibers by means of extrusion. Prior to processing, the material must be milled and dried. The extruder must operate at temperatures between 180 and 230° C and must allow the passage of softened and unmelted particles of material. With the process described above homogeneous products of various sizes may be produced without or with only a minimum admixing of additives to the output material.

Description

Process for Mechanical Recycling of Composite Polymeric Material

The invention relates to a process for mechanical recycling of waste composite polymeric material into products of various dimensions. The waste composite polymeric material for recycling according to the invention consist of 30-40 parts (by mass) of unsaturated polyester resin reinforced with glass fibers, 30-60 parts of partially cross-linked polymethylmetacrylate, and 0-70 parts of acrylonitrile-butadiene-styrene (ABS) copolymer. Such composite materials are generally used for producing load bearing products of larger dimensions, such as bathroom elements, playground slides, or crafts. The recycling of such composite materials is hampered by the constituting components being hard to separate and by the fact that unsaturated polyester resin and partially cross- linked polymethylmetacrylate are not thermoplastic materials which could be reshaped in melted form. Consequently, waste from such composite materials is generally discarded on waste dumps. Known methods for recycling waste composite polymeric material are based on the thermoplastic material forming the bulk of the mixture and flowing over the remaining mixture components which act as fillers. The most widely used processes make use of extruders resistant to abrasion, while the percentage of the thermoplastic material according to manufacturers' recommendations shouldn't be less than 70%. Such method could also be employed for said composite polymeric material, in which case, however, the overall quantity of the material would increase enormously due to the additional thermoplastic material (admixed in order to constitute about 70% of the final mixture) . The present invention solves the technical problem of recycling mixed polymeric waste from cross-linked polymers without or with only a minimum addition of thermoplastic materials. Published inventions in the field of recycling of polymeric composites from cross-linked polymers are based on methods of depolymerization and reutilization of the products (WO 03/051956 Al) , on the use of solvents at elevated temperatures (WO 01723463 Al, US 2002/0017162 Al) , or on the pyrolysis process (WO 02/088277 Al) . Said methods require a high energy intake and belong to the field of the so-called chemical recycling methods wherein the polymer is mainly decomposed or treated chemically. Mechanical recycling of a composite waste consisting chiefly of polyester resin is described in patent EP 1 273 627 Al, said patent, however, relates to a material composition that differs substantially from the material described in the present invention. The object of the invention is a process for recycling composite polymeric material with low content of thermoplasts that is technologically simple, not energetically exacting, and economical. According to the invention, the object is achieved by the process for mechanical recycling of waste composite polymeric material as set forth in the appended patent claims . The process of the invention is based on extrusion of milled mixed waste. Due to the nature of the material, the extruder must be provided with an Archimedean screw permitting the undisturbed flow of unmelted, softened particles of the milled material. The size of the particles and consequently the form of the Archimedean screw depends on the preliminary treatment of the material during the milling and/or sifting process. The extruder must be provided with external heating allowing temperatures to be achieved at which a drop in viscosity (partial melting) of the polyester, polymethylmetacrylate and/or ABS occurs. Extruders with a single or a double Archimedean screw may be used, with or without the capability of degassing the heated material. In the embodiment, an extruder with an Archimedean screw at least 25 mm in diameter and temperatures between 180 and 230° C were employed. Prior to processing, the material must be milled to a particle size that will allow undisturbed feeding of the material into the extruder, which mainly depends on the feeding method, the inlet openings and the diameter of the Archimedean screw. In order to achieve homogeneity and a relatively smooth surface of the product, the material must be dried to a constant mass containing no humidity prior to processing. The ABS copolymer content may be varied arbitrarily, but this will affect the processing properties of the material. With little or no ABS molds may be cast and simple shapes extruded, whereas by increasing the percentage of ABS more complex shapes may be extruded. Passing through the extruder the mixed waste is stirred and softened by heat. The softened polyester, polymethylmetacrylate and ABS bond together the unmelted polymeric particles and glass fibers, so that a homogeneous mass, shaped into a continuous profile exits the apparatus. The shape of the profile depends on the chosen outlet nozzle, which is to say, on the purpose of the product. The product may also be shaped by introducing the softened material into metal moulds of various forms and sizes. Cooled products achieve strengths comparable to the strengths of chipboards. Although bigger particles of polymethylmetacrylate, polyester resin and fibers are noticeable on the surface and section, they are solidly bound together. The product does not absorb water or swell in the presence of humidity. A layer of polymethylmetacrylate, conferring a flawless external appearance to the product, may be deposited onto the surface of the product during the continuous extrusion process by means of co-extrusion. The invention described herein improves the process for mechanical recycling of a polymeric composite based on polymethylmetacrylate, ABS, unsaturated polyester resin and glass fibers. The main advantage of the described process is in that it provides economically viable mechanical recycling of great quantities of mixed polymeric waste without or with only a minimum content of thermoplastic materials, binders or other additives which could increase the processing costs and the quantity of the processed material .

First embodiment

A composite consisting of: 50 % polymethylmetacrylate, 30 % unsaturated polyester resin and 20 % glass fibers was milled to a maximum particle size of 11 mm. The obtained mixture was then fed to a single-screw extruder having an Archimedean screw of 25 mm in diameter. The extrusion took place at a temperature of 220° C. The obtained full profile was compact, homogeneous and solid after cooling down. The interior of the profile was homogeneous and without any air bubbles. There was no thermal overheating or uncontrolled thermal breakdown of any of the components of the mixed material in the course of processing.

Second embodiment

A composite consisting of: 50 % polymethylmetacrylate, 35 % unsaturated polyester resin and 15 % glass fibers was milled to a maximum particle size of 15 mm. The obtained mixture was then fed to a single-screw extruder having an Archimedean screw of 60 mm in diameter. The extrusion took place at a temperature of 190° C. The melted mixture was then poured directly into a metal mould until full. At that point the supply was interrupted, the mould was closed and left to cool down to a temperature of approximately 50° C. The mould was then opened and the product extracted. The section of the product showed its interior to be homogeneous .

Third embodiment

A composite consisting of: 50 % polymethylmetacrylate, 10 % acrylonitrile-butadiene-styrene copolymer, 25 % unsaturated polyester resin and 15 % glass fibers was milled to a maximum particle size of 15 mm. The obtained mixture was then fed to a single-screw extruder having an Archimedean screw of 60 mm in diameter. The extrusion took place at a temperature of 190° C. The obtained tube with a wall thickness of 5 to 7 mm was compact, homogeneous and solid and without any air bubbles after cooling down.

Fourth embodiment

A composite consisting of: 33 % polymethylmetacrylate, 40 % acrylonitrile-butadiene-styrene copolymer, 17 % unsaturated polyester resin and 10 % glass fibers was milled to a maximum particle size of 15 mm. The obtained mixture was then fed to a single-screw extruder having an Archimedean screw of 60 mm in diameter. The extrusion took place at a temperature of 190° C. The profile was sized. The obtained rod with a diameter of 35 mm was compact, homogeneous and solid and without any air bubbles after cooling down.

Therefore, the process for mechanical recycling of waste composite polymeric material from partially cross- linked polymethylmetacrylate, acrylonitrile-butadiene- styrene copolymer, unsaturated polyester resin and glass fibers into products of various sizes is characterized in that prior to processing the material is milled to a convenient particle size for feeding into the extruder, and that the process takes place in an extrusion apparatus (extruder), heated to a work temperature of 180 to 230° C. The material consists of 30-40 parts (by mass) of unsaturated polyester resin reinforced with glass fibers, 30-60 .parts of partially crbss-linked polymethylmetacrylate, and 0-70 parts of acrylonitrile- butadiene-styrene (ABS) copolymer. The extruder allows the passage of unmelted particles of material. The material must be dried to a constant mass containing no humidity prior to processing. The mass exiting the extruder is shaped into a continuous profile of various sections, depending on the chosen outlet nozzle, which is to say, on the purpose of the product. A layer of polymethylmetacrylate may be deposited onto the continuous profile by means of co-extrusion. The mass exiting the extruder may also be shaped by introducing it into moulds of various forms and sizes. The process of the invention is economical in terms of energy and material, not requiring great inputs of energy or additional materials. Therefore, the invention is specific and economically effective. The embodiments described above are by way of illustration only and shall have no limiting effect on the scope of the invention.

Claims

Patent Claims

Process for mechanical recycling of waste composite polymer material, characterized in that said material consist of 30-40 parts (by mass) of unsaturated polyester resin reinforced with glass fibers, 30-60 parts of partially cross-linked polymethylmetacrylate, and 0-70 parts of acrylonitrile-butadiene-styrene (ABS) copolymer, that prior to processing the material is milled to a convenient particle size for feeding into the extruder, and that the process takes place in an extrusion apparatus (extruder) , heated to a work temperature of 180 to 230° C.

Process according to Claim 1, characterized in that the extruder allows the passage of unmelted particles of the material.

Process according to Claim 1, characterized in that prior to processing, the material is dried to a constant mass containing no humidity.

Process according to Claim 1, characterized in that the mass exiting the extruder is shaped into a continuous profile of various sections, depending on the chosen outlet nozzle and the purpose of the product.

Process according to Claim 4, characterized in that a layer of polymethylmetacrylate is deposited onto the continuous profile by means of co-extrusion.

Process according to Claim 1, characterized in that the mass exiting the extruder is shaped by introducing it into moulds of various forms and sizes.