industrial plastics waste containing high amounts of paper. Such materials can- not be reprocessed without adding a polyolefin-containing fraction, in this case post-consumer waste from Kolding in Denmark. The approximate compositions of the samplesA-Daregiven in Table 1. Hydrolysis All samples were groundinamill (Rapid GK 20,high-speed rotation knife mill, normally fitted with a 25 mm screen). When subjectingthewaste material to the hydrolytic treatment, three methods can be employed: • hydrolysis in suspension • hydrolysis after impregnation with the acid solution and drying • hydrolysis with acid in the gas-phase. C. Klason, J. Kubát, and H.R. Skov 113 Table 1 Approximate composition of samples A-D Material Sample A (%) Sample B (%) Sample C (%) Sample D (%) LDPE 27 20 70 90 HDPE 5 65 <1 LDPE&HDPE PP 2.5 15 PS 7 PVC hard 4.5 10 PVC soft 1.5 other plastics PA 1 PET 4.5 Thermosets 0.5 Cellulose 46 varying 30 varying Aluminum 0.5 <1 Other materials Country Sweden Denmark Denmark Italy All these methods were discussed previously. 3 Using the first method, the waste material was suspended in the acid solution (solid/liquid ratio 1/9) and the mix- ture boiled for about one hour. Mineral acids with aconcentration of 5-10% were used in this case. With solutions of organic acids, a simple boiling was not suffi- cient, and the pretreatment had to be carried out at elevated temperatures in a pressure vessel. A typical example is a treatment in 3 % oxalic acid solution at 121 o C (pressure 2 bars). The hydrolyzed product was then washed with a tap water until neutral, and dried at 50 o C for several days (moisture content below 4%) before milling. The low temperature was chosen in order to preserve the original fibrous structure of the cellulose component. However, the weight loss of the cellulose component was typically 5-20%, depending on the extent of the hydrolytic breakdown. A technique circumventing the weight loss problem is based on impregnating the material with the acid solution and subsequently drying it at elevated tem- perature. In this case the waste was impregnated with a dilute solution of an or- ganic acid such as citric or tartaric acids for an hour, then an excess acid was removed by vacuum filtering and the material was pre-dried at 105 o C for 12 hours. The actual hydrolytic process took place during homogenization of the material in the compounding extruder at 190 o C. These two methods of hydroly- sis proved feasible, producing comparable results whentestedwith LDPE waste containing 30% newsprint (waste from the Lövsta Plant in Stockholm and from the Idelux Plant, Arlon, Belgium). 4 In principle, one of the most positive results following hydrolysis is the improvement in processability. The viscosity of the untreated melt was more than twice as high as that of the hydrolyzed sample, and it also showed significant fluctuations during the experiment. These differ- ences appear to be associated with thesize distribution of the paper fibers in the melt. The average particle size was approximately 20 µ m and the sample con- tained less than 1% of particles larger than 100 µ m for samples subjected to hy- drolysis. The mean fibre length of unhydrolyzed fibers after injection molding was 800 µ m; there was also a large number of agglomerates (parts of paper) in the melt. However, a more industrially applicable method of reprocessing paper-con- taminated plastics waste of various origins is the gas-phase method. A semi-pi- lot plant reactor was constructed in order to handle larger quantities of waste (previous methods some kg). The reactor tank (length 1 m, inner diameter 0.64 m, volume 300 liters) was built of stainless steel. The plastics waste and/or the 114 Hydrolytic Treatment of Plastic Waste Containing Paper paper component was fed into the reactor by a single screw (75 mm diameter), and the material was circulated inside the reactor by a slow-moving PTFE-coated stirrer, which prevented the plastics parts from sticking to the wall. The temperature was monitored and adjusted by a thermocouple inside the reactor. The reactor was flushed with carbon dioxide and the selected test temperature was set above the boiling point of an acid, which was added to ob- tain a superheated gas phase. Different gases were used, but the best results, from the point of view of environmental protection, were obtained with formic acid. The 1.2kg of formic acid (concentration85%, technical quality) per m 3 reac- tor volume was found to be an adequate dose for the hydrolytic treatment. The time of hydrolysisin this reactor was quitelong and varied from 1to 3 hours. The temperature varied between 150 and 240 o C. The mixture of paper and molten plastics flowed towards the bottom of the reactor by gravity, the melt tempera- ture was monitored, and the melt was finally extracted with a double screw (di- ameter 100 mm) into a water bath to prevent oxidation and achieve rapid cooling. Typically, batch sizes of 25 kg could be handled in this reactor. After hydrolysis the material was ground in the knife mill fitted with an 8 mm screen and stored dry until processing (compounding). The reference material, which was not hydrolysed, was also ground once more with the 8 mm screen fit- ted to the mill. Processing On a laboratory scale the material was melt-homogenized in a compounding machine (Buss-Kneader PR46). The residence time in the extruder was short, approximately 2 minutes. At a melt temperature of 240 o C, a good homogeniza- tion of the material was obtained. For samples containing only polyolefines, 180 o C was sufficient to obtain good homogenization of the material. The com- pounded material was milled in the knife mill (8mm screen) and dried at 105 o C for 24 hours prior to injection molding. Some samples (B, C, and D) were also melt-homogenized in a larger machine specially designed for mixed plastics waste, at the Cadauta plant in Italy. The machine (“Revive” compounder from Cerrini, Busto Arsizio, Italy) has a screw diameter, D, of 120 mm, and a cylinder length of 30D. It is a slow running ma- chine (33 rpm). The melt temperature was set at 240 o C, but due to the special construction of the machine a high shear-induced heat gradient in the melt was C. Klason, J. Kubát, and H.R. Skov 115 bly much higher than the set temperature. The slow screw speed results in lon- ger residence time (approximately 15 minutes) than in the Buss-Kneader. The compounded material was injection-molded into tensile test bars (cross section 3.5 × 10 mm 2 and an effective length of 75 mm) using a conventional ma- chine (Arburg Allrounder 211E/171R). The injection pressure was adjusted to obtain satisfactory moldings (upper limit 150 MPa). The melt temperature was 190 o C. In some cases the material was injection-molded into thin-walled prod- ucts, so called Raschig-rings, in Italy at the Cadauta plant using a normal injec- tion molding machine. These rings are normally made of PP, and the holding pressure had to be increased by 50% in order to obtain satisfactory moldings us- ing the hydrolyzed samples. RESULTS The post-consumer plastics waste, sample A, collected from households in Gothenburg contained two different paper components: milk packages (lami- nated board) and newsprint. Laminated board is normally very difficult both to grind and to reprocess. Sample A contained 46 % paper and was found impossi- ble to injection-mould without hydrolysis. The stiffness of sample A subjected to hydrolysis is very high (E-modulus 3.9 GPa, strength at break 15 MPa, elonga- tion 1.2%, impact strength 9 kJ/m 2 ; Charpy test). This is a result of the large amounts of PS and PVC and a high cellulose content. The presence of PS and PVC makes sample A very brittle. In essence, the CUT-method was found to be the only way to make sample A moldable on a laboratory scale. Sample B, the plastics waste from Skive in Denmark mixed with edge trim- mings from the packaging industry (in total30% paper loading), was used in the tests to evaluate the influence of time and temperature using formic acid in the semi-pilot plant reactor. Inthese experiments it was found thatthe thermal con- duction was low. The mechanical properties such as modulus, strength, the cor- responding elongation at break, and impact strength are given in Figure 1 as a function of the melt temperature at the bottom of the reactor. The values given at room temperature (RT) in Figure 1 refer to the unhydrolyzed samples. The time to reach the set temperature was approximately 1 hour. It is clear from the E-value and IS-value data that the cellulose component, and probably the poly- mer as well, were subjected to severe thermal degradation for reaction tempera- tures above 200 o C. In general, it can be concluded that the optimum 116 Hydrolytic Treatment of Plastic Waste Containing Paper obtained. Therefore, the actual melt temperature is not known, but it is proba- lot reactor is approximately 2 hours (one hour to reach set temperature). Both unhydrolyzed and hydrolyzed samples (samples B, C and D) were com- pounded at the Cadauta plant in Italy using the “Revive” extruder. 5 After com- pounding, the granulated materials were injection-molded into test bars as well as into molded cylindrical thin-walled parts (rings, see Figure 4 below). The samples containing 30%paper could be compounded without difficulty us- ing the “Revive” machine. The results obtained on the molded test bars are C. Klason, J. Kubát, and H.R. Skov 117 Figure 1. Influence of the hydrolysis temperature (melt temperaturein the ractor) on themechani- cal properties of plastic waste containing 30% paper. Sample B, formic acid in gas phase, treatment time 3 hours. Values at room temperature (RT) refer to the unhydrolized sample. temperature of hydrolysis is approximately 180 C, and the time in the semi-pi- • the E-modulus decreased with hydrolysis, due to fibre length reduction • the strength value was almost unaffected by hydrolysis • there was an increase in elongation at break and in impact strength for the samples subjected to hydrolysis. In a series of experiments the cellulose content was varied between 18 and 45 % by changing the portion of paper component added to sample D. The improve- ments in elongationat break following hydrolysis areillustrated in Figure 3 (un- filled symbols - unhydrolyzed samples; filled symbols - hydrolyzed samples). 118 Hydrolytic Treatment of Plastic Waste Containing Paper Figure 2. The mechanical propertiesof untreated and treated (formic acid in gasphase,200 o C, 3 h) plastic waste, sample D, containing 30% paper. Sample D without paper: modulus - 1.1 GPa, strength − 17 MPa, elongation at break-exceeding250%,nobreakindicationatimpacttesting. samples C and D: shown in Figure 2 (sample D). The following behavior was observed for both C. Klason, J. Kubát, and H.R. Skov 119 Figure 3. Elongation at break and E-modulus vs. paper content for untreated (unfilled symbols) and treated sample D (filled symbols, formic acid in gas-phase, 200 o C, 3 h). The strength values are not influenced to a great extent for different paper con- tents (strength at break approximately 12 MPa), but the E-modulus values in- crease with increasing paper content for both unhydrolyzed and hydrolyzed samples as shown in Figure 3. Also, the flow behavior, as measured by spiral molding tests, was found to be improved 20% by thehydrolysis as a consequence of the reduction of a fibre length of a cellulose component. These short fibers do not act as reinforcing fibers and the adhesion between the fibers and the matrix is poor; thus the strength is not improved by the incorporation of paper. The stiffness, on the other hand, is naturally increased for increasing paper load be- cause of a high modulus of the fibers (approximately 20 GPa). In general, the re- sults are in an agreement with earlier findings for PP filled with hydrolyzed cellulose. 6 Some of the samples compounded on the “Revive” machine were injec- tion-molded in Italy into thin-walled rings from material B, see Figure 4. The re- sults showed that thin-walled components containing 30% paper could be injection-molded (hold pressure has to be increased by 50%). When the paper content was reduced to 15% the components made out of sample B showed good elasticity and good surface finish for the hydrolyzed samples (E-modulus 1.1 GPa, strength 12 MPa and elongation at break 10%). Samples C and D could also be injection molded into rings (sample A not tested). 120 Hydrolytic Treatment of Plastic Waste Containing Paper Figure 4. Photograph of injection-molded thin-walled parts (rings). Molded in Italy by Cadauta, S. Sebastiano da Po, Torino (sample B). Total width 310 mm, total mass, including runner 25 g, mass of each part 2 g (cylindrical, diameter 25 mm, height 25 mm, wall thickness 1 mm). These rings are normally made of PP. CONCLUSIONS The results presented here demonstrate that significant improvements in the homogeneity and processability of plastics waste of different compositions and origins contaminated with paper can be achieved using a relatively simple hydrolytic treatment. Such treatment improves the mechanical properties of the material, and PFMW and similar plastics waste containing as much as 40% paper become processable into products with acceptable surface appearance. The paper content at which the hydrolysis makes the most pronounced impact on the properties of the material seems to be in the range 20 to 30 %. However, the greater homogeneity of the paper-containing samples following hydrolysis is in many cases a desired property, even at very low paper content, specially when molding thin-walled products. The gas-phase technique isaneconomical method of hydrolysis which seems to be adaptable to the industrial practice. The temperature of hydrolysis must, however, not exceed 180 o C. On an industrial scale the hydrolysis may be per- formed in a screw reactor in order to improve temperature control. In conclusion, the method of hydrolysis offers an efficient and economical way of processing plastics waste, both post-consumer waste and industrial waste, contaminated with a cellulose component. The addition of cellulose gives a de- sired stiffness to the final product, as reported in earlier publications. 4,6 Thus, the plastics waste containing a cellulose component can be used in several appli- cations, such as artificial wood. ACKNOWLEDGMENT The support of the Commission of the European Communities and of the Na- tional Swedish Board for Technical Development infinancingthis work is grate- fully acknowledged. REFERENCES 1. S. Gotoh, in Sorting of Household Waste and Thermal Treatment of Waste, Eds. M. P. Ferranti and G. L. Ferrero, Elsevier, London, pp. 441-443, 1985. 2. C. Klason and J. Kubát, Sw. Patent and Eur. Pat. Appl. 8107444-5,US4,559,376. 3. C. Klason, J. Kubát, A. Mathiasson, M. Qvist, and H. R. Skov, Cellulose Chem. Tech, 23, 131 (1989). 4. A. Mathiasson, C. Klason, J. Kubát, and H. R. Skov, Resources, Conservation and Recycling, 2, 57 (1988). C. Klason, J. Kubát, and H.R. Skov 121 Eds. M. P. Ferranti and G. L. Ferrero, Elsevier, London, pp. 441-443, 1985. 6. A. Boldizar, C. Klason, J. Kubát, P. Näslund, and P. Saha, Int. J. Polym. Mater., 11, 229 (1987). 122 Hydrolytic Treatment of Plastic Waste Containing Paper 5. R. Fornasero, in Sorting of Household Waste and Thermal Treatment of Waste, [...]... number of plastics used and the disproportionately high costs in the dismounting of the different plastic pieces of a car have a negative impact on the recycling process As a result of this, only the metallic fraction is recovered, while the plastic materials continue to be eliminated by deposition in refuse dumps To solve this problem CSI has developed a concept based on the use of materials of the... within the automotive industry Plastic materials have initially replaced materials such as leather, wood, textiles made from natural fibers and steel in the car interior and lately they have also been appearing as body components and accessories Because of the advantages in design and functionality, plastics are now an indispensable part of any kind of car and the amount of polymers employed to build... greater than that of samples 1 28 Processing of Mixed Plastic Waste Figure 4 Parking area Table 4 Mechanical properties of PVC fraction/virgin PVC Material PVC fraction Virgin PVC IZOD impact strength (notched) (J/m) Tensile properties (elastic modulus) (MPa) 60 281 0 40-90 3000 produced from mixed plastics Currently we are working on a procedure that separates four fractions of different materials These... others The majority of these articles are composed of thin protective films, sheeting for blisters, strapping, thermo-formed trays, as well as a variety of bottles for soft drinks, food and cosmetics As shown in Figure 1, there are mainly five different polymers that contribute to the total amount of plastic waste, and they are commodities (PE, PP, PS, PVC, PET) The plastic composition of the above mentioned... the regional habits and the seasons of a year Also the mode of a waste collection can influence its final composition The category of plastic waste from the industrial sectors concerns the medium/long life articles like the products for cars industry, furniture, appliances, etc The problem of these sectors is a wide variety of engineering materials and a high number of components employed to build a... final system This paper reports two recycling approaches adapted in CSI to establish appropriate technologies and/or design concepts for the above mentioned groups of plastic waste MIXED PLASTICS FROM HOUSEHOLD WASTE A study of this type of a plastic waste has been performed at CSI using samples that came from two different experimental collection systems, the first in plastic 3 boxes (internal volume:... the use of materials of the same family for all components of the plastic systems to be recycled at the life end This allows an easy and direct recycling of the scraps and the recovery of the whole system Greater recycling efficiency will be obtained when the following two basic requirements are satisfied : • materials compatibility through materials homogeneity • easier disassembly through planned... reuse of the PET fraction implies that the amount of residual PVC must be kept below 50 ppm to avoid undesirable polymer degradation This degradation determines poor surface appearance and loss of mechanical properties of the manufactured products PLASTICS FROM INDUSTRIAL SECTORS As mentioned before, plastic waste from the industrial sectors concerns the medium/long life articles The main problem of these... (MPa) 16.5 8. 0 20.5 16.5 19.0 11.2 700 82 0 24.5 6 .8 4.3 2 950 1250 280 0 Table 2 reports some mechanical property improvements obtained through an addition of several components As shown, the glass fibers allow the product to obtain a very high stiffness, higher than that with talc and far better than that of the original mixture, while the SBS and PE improve the tenacity The final choice of a type and... properties of polyolefin-based fraction are far better than those of the heterogeneous mixture The improvement of tenacity is, in particular, evident when considering impact resistance Samples subjected to impact tests show an increase in elongation at the breaking point from 7 percent to above 100 percent As well as for polyolefins, the properties of recycled PVC fraction are comparable with those of a . large number of plastics used and the disproportionately high costs in the dismounting of thedifferent plastic pieces of acar have a negative impact on the recycling process. As a result of this,. technologies and/or design concepts for the above mentioned groups of plastic waste. MIXED PLASTICS FROM HOUSEHOLD WASTE A study of this type of aplastic waste hasbeen performed at CSIusing samples that. Processing of Mixed Plastic Waste Figure 1. Mix composition. of organic materials following the washing step. Due to the presence of PVC resin, the melting temperature must be kept below 483 K and