REUSE OF REINFORCED ACRYLIC PLASTIC WASTE IN NEW COMPOSITE MATERIAL DEVELOPMENT

Transcription

1 5th International DAAAM Baltic Conference "INDUSTRIAL ENGINEERING ADDING INNOVATION CAPACITY OF LABOUR FORCE AND ENTREPRENEURS" April 2006, Tallinn, Estonia REUSE OF REINFORCED ACRYLIC PLASTIC WASTE IN NEW COMPOSITE MATERIAL DEVELOPMENT Kers, J., Kulu, P., Goljandin, D. & Mikli,V. Abstract: This study had two aims: to develop prospective techniques for recycling of composite plastic wastes and to find a potential application area for secondary raw materials. The method of collision was selected for the treatment of composite plastic wastes and a disintegrator mill was used. In our experiments, the particle size of acrylic plastic was reduced and glass fibers intact were separated. The paper describes the results of materials separation, granularity of the milled material and morphology of the plastic powder particles. To develop new filler materials for fillerresin systems, plastic powders with different granularity were used. The mechanical properties of the new composite materials were examined. The developed new acrylic powder filler materials are prospective for use in the filler-resin systems as reinforcement acrylic cells. Key words: environmental friendly technology, waste management, composite plastic waste, recycling, disintegrator mill 1. INTRODUCTION Wastes are produced in each manufacturing plant. Every producer should manage its waste effectively to protect the environment against contamination. According to EU waste directives, hierarchy of waste management is: 1) prevention, 2) reuse, 3) recycling, 4) energy recovery, 5) incineration without energy recovery, 6) landfill. As it follows from directives 2000/53/EC on ELV and 2002/96/EC on WEEE, the producers are responsible for environment protection during their product lifecycle. The producers should form the producers responsibility organizations to manage the collection and recycling of post-consumer products. To meet these requirements, two solutions can be proposed. Firstly, to extend the lifecycle of the product in combination of durable materials and a durable design. Secondly, to extend the lifecycle of the materials to reduce environmental impacts related to materials manufacturing and transportation. Finding a solution for the reuse of production waste will help to recycle post consumer products in future. The interest of this study lies with Estonian bathroom equipment manufacturing companies. In their point of view, the composite plastic wastes (vacuum formed acrylic plastic with glass fiber reinforcement) have low volume weight and thus have to be precrushed to save transportation and landfilling costs. 2. EXPERIMENTAL 2.1 Plastics to be recycled Industrial polymethylmetacrylate (PMMA) wastes can be divided into two groups: acrylic plastic wastes, without technological additives form about 20 % and reinforced acrylic plastic wastes about 80 % of the total amount. The acrylic plastic wastes without technological additives could not be recycled and re-extruded to produce the new PMMA sheet material, because of the 267

2 amorphous structure of this thermoplastic material. Heating up the acrylic plastic material over the glass transition temperature (100 C) converts the plastic in to a rubber-like state, which makes this material ideal for vacuum forming. Continued heating will cause thermal degradation instead of melting the material. Physical and mechanical properties of the plastics to be recycled are given in Table 1. Table 1. Physical properties of milled plastics Material (23 C) Tensile strength N/mm 2 Tensile modulus MN/mm 2 Impact strength kj/m 2 Density kg/m 3 PMMA PE-resin GFP PMMA sheet material, vacuum-formed and reinforced with glass fiber plastic (GFP) in the matrix of polyester resin, was used as the composite plastic waste. 2.2 Retreatment technology For the milling of the composite plastic waste, different disintegrator types developed at Tallinn University of Technology were used [ 1 ]. As a result of our previous study the 20 %wt. of the industrial acrylic plastic wastes was retreatable by high energy disintegrator mills [ 2 ]. Thus, we assumed that we made assumption that the high energy mill can be used for the remaining 80% wt. To recycle the composite plastic waste, we then focused on the size reduction of the acrylic plastic constituent and the separation of the glass fiber constituent. Disintegrator milling offers the possibility of milling with a simultaneous separation of components with low toughness properties [ 3 ]. Composite plastic stripes (PMMA+GFP) with dimensions of 500 mm length, mm of width, and a thickness of 5 mm were retreated by the mechanical method milling by collision. The retreatment technology consisted of three steps: preliminary milling of reinforced acrylic stripes in the DSL-158 disintegrator to separate the GFP pieces from the milled acrylic plastic sieves were used; intermediate milling in the DSA-2 disintegrator to reduce the size of GFP pieces for a feed of DSL-115; final milling in the DSL-115 disintegrator, using the direct and selective milling system to remove glass fiber from the milled material. 2.3 Granularity and morphology study In this study, particle size of acrylic plastic powder was characterized by sieving analysis (SA) and image analysis (IA). To characterize particle shape, the image analysis was used. To evaluate coarse powder granularity (particle size more than 50 µm), the sieve analysis ensuring sufficiently good results was used. Particle size distribution is adequately described by the modified Rosin-Rammler distribution function, and the method may be used to characterize powders produced by collision. Particle size data obtained by the image analysis method was primarily described through the arithmetical mean diameter d m of the measured values. The values of d m depend on the number of particles. To characterize particle shape the IA method was used and the following shape factors were calculated: the elliptic parameter; to characterize ellipticity, aspect ratio AS (similar to elongation in literature) was calculated by AS = a/b, (1) where a and b are the axes of the Legendre ellipse (ellipse is an ellipse with the centre in the object s centroid and with the same geometrical moments up to the second order as with the original object area). the irregularity or surface smoothness; the shape factor roundness RN value was calculated by RN=P 2 /4πA (2) where P is perimeter and A is area of the particle. Roundness of the circle is equal to 1. In all other cases, roundness it is greater than 1 [ 4 ]. 268

3 3. RESULTS AND DISCUSSION 3.1 Recycling of composite plastic waste As it follows from Fig. 1, an intensive size reduction (80% of particles less than 25 mm) of composite plastic takes place by the preliminary milling in the DSA-158 disintegrator. f(m), % Precrushing 0.2 kwh/ T Size d ( mm) Fig. 1. Dependence of the distribution function of composite plastic particle size on the specific energy of treatment The results of the separation of glass fiber plastic from the composite plastic waste are given in Table 2. Table 2. Results of separated GFP Milling stages Milling device Separation method I DSA-158 Sieves 16.3 II DSA-2 Sieves 12.2 III DSL-115 Air classifying 16.5 Separated GFP, wt% As it follows from Table 2, the total amount of separated GFP was 45 wt%. As a result, we can reuse 55 wt% of acrylic plastic from the composite plastic waste. It is important to find a future application for GFP. One of the possible areas for reuse of GFP is in the production of polymeric concrete products as reinforcement. 3.2 Study of the particles shape The data necessary in a particle size study were obtained using an image processing system, which consisted of a Nikon Microphot-FX, an optical microscope (OM) and a video transferring system. Measurements were performed in the transmission regime of OM, because of more accurate results of particle size obtained as compared to a reflected regime. The size and shape parameters were determined using image analysis Image- Pro Plus 3.0 system. Morphology studies of acrylic plastic powder particles showed the roundness parameter RN 1.32 for powders with a mean particle 600 µm and the specific energy of treatment 12 kwh/t and RN 1.31 for powders 300 µm and the specific energy of treatment 50 kwh/t. 3.3 Reuse of the milled product Preliminary tests to find the application areas of acrylic powder as a new filler material were made by using the Solid Surface casting technology. For example, most of bathroom washbasins are produced by casting technology. Commonly, washbasins are made from a composite material consisting of a binder agent (unsaturated polyester resin), a filler material (dolomite powder) and a catalyst agent added to resin to accelerate hardening. The mixing ratios of the binder agent and the filler material are 25/75 wt%. The traditional filler material used in the casting technology is a high-white dolomite filler with the chemical composition of CaMg (CO 3 ) 2 with a density of 2850 kg/m 3 and particle sizes of coarse fractions ( mm), ( mm) and fine fraction (less than 0.1 mm). For this purpose, the composites were designed with different mixing ratios of the binder (unsaturated polyester resin) and the filler (acrylic powder). The filler volume varied from 50 to 65 wt%. The filler consists of 50 wt% of coarse fraction ( mm) and 50 wt% of fine fractions ( mm) of acrylic powder material. 1 wt% of peroxide catalyst was added to accelerate the polymerization, for 269

4 transforming from liquid to solid state with maximum physical properties; The liquid mixture of the composite was cast into a plate shape mould (500 x 500 mm 2 ) with a layer thickness of 15 mm. We assumed that by increasing the acrylic filler content the mixed polyester resin will ensure the hardness and good wear resistant properties of the working surface of the washbasin. The hardening time of the composite was four hours. The best flow characteristics of the mixture were with 50 wt% of acrylic filler and 50 wt% of resin, but the best surface quality and hardness after polishing was achieved by the mixture of 66 wt% of acrylic filler and 33 wt% of resin. The flow characteristics of the mixture 66/33 could be improved by using a lower viscosity binder agent. 3.4 Mechanical testing of the new composite material Mechanical properties of the new composite materials were determined. Using specimens of plastic composites (in different compositions of the filler and binder agent) were made according to ISO and DIN standards. Mechanical properties of the plastic are primarily defined by the tensile strength of the material. Unlike metals, the utmost influencing factor for plastics is temperature. Therefore it is important to know the minimum and maximum working temperatures of the plastic which are not entailing the changes in physical and mechanical properties of the material. The tensile strength of composite plastic materials mainly depends on the adhesion strength between the resin matrix and reinforcement. For glass fiber plastics, the direction of reinforcement is important (uni-axial, bi-axial, multi-axial). In our case, the new composite plastic material consists of polyester resin matrix and granular reinforcement (acrylic plastic), instead of fibers. Test specimens were machined from cast plate material in accordance with ISO 527-2/1A/50 standard and specimen type was 1B. To compare the test results, specimens of acrylic sheet material were made. The tensile test of the new composite materials 33/66 gave an average tensile strength 15 N/mm 2. The tensile strength of an acrylic plastic specimen was 42 N/mm 2. We assumed that the pores inside the material influence the tensile strength of the new composite material. To determine the percentage and the size of the pores, the microsection of the composite material was prepared. 3.4 Porosity of the composite material To study the porosity of the cast composite material, specimens (50 mm length, 50 mm width, and thickness 10 mm) were made. The surfaces of the specimens (top, bottom and cross section) were ground and polished. The photos of the surfaces of the specimen were taken and the pictures were processed (see Fig.3). Fig. 3. Porosity of the composite material The images were analyzed with Image-Pro Plus 3.0. Firstly, the surface areas of the matrix and the pores were calculated. The total area of the pores was 6.5 %. The pore size data obtained by the image analysis method were primarily described through the arithmetical mean diameter d m of the measured values (see Fig. 4). The mean diameter of the pores was 97 µm. As it was mentioned above an increase in the acrylic filler content in mixed polyester resin ensures strength and hardness of material, good wear resistance properties for the surface of the materials. 270

5 Percent Mean diameter dm, µm Fig. 4 Mean diameter of the pores Therefore it is important to determine the optimal size and shape of particles in the composite. 2. The retreated material can be reused in the same production process where they are generated. 3. The aim of further study is to design a composite material for washbasin production. Washbasins made from the designed new composite material, using retreated plastics, would have a good wear resistance of the working surface because of the hardness of the acrylic material. At the same time they will weight two times less than produced of the dolomite filler. 5. REFERENCES Fig. 5 Particle size and shape inside the composite matrix. As it follows from Fig. 5. the mean diameter of the particle in surface was 105 µm. The mean roundness parameter RN of particles was 1.56 and the mean aspect AS was CONCLUSION 1. The existing advanced technologies for size reduction mostly using 1 to 4 rotor(s) with knives and the resulting size of the final product (20-40 mm) not applicable as a filler material in the casting technology, however it suits for further size reduction by milling in disintegrators. A high-energy powder with a particle size of about 1-2 mm by two-step milling and 95 wt% glass fiber content can separate by final selective milling. 1. Tamm, B. and A. Tymanok, Impact grinding and disintegrators. Proc. Estonian Acad. Sci. 1996, Eng., 2/2, , 2. Kers, J. and P. Kulu, Retreatment of industrial plastic wastes by high energy disintegrator mills, In proc. of Global Symposium on Recycling, Waste Treatment and Clean Technology, Madrid 2004 Vol. 3, Kulu, P. and A. Tymanok, 1999, Treatment of different materials by disintegrator systems, Proc. Estonian Acad. Sci. Eng. 1999, 5/3, Wojnar, L., Image analysis: applications in materials engineering. CRC Press LLC, Boca Raton, CORRESPONDING AUTHOR J. Kers Department of Materials Engineering Tallinn University of Technology Ehitajate tee 5, Tallinn 19086, Estonia. j.kers@mail.ee 271

6 272