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The post-consumer plastics waste, sample A, collected from households in Gothenburg contained two different paper components: milk packages (laminated board) and newsprint. Laminated board is normally very difficult both to grind and to reprocess. Sample A contained 46 % paper and was found impossible 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, elongation 1.2%, impact strength 9 kJ/m2; 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 trimmings from the packaging industry (in total 30 % paper loading), was used in the tests to evaluate the influence of time and temperature using formic acid in the semi-pilot plant reactor. In these experiments it was found that the thermal conduction was low. The mechanical properties such as modulus, strength, the corresponding 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 polymer as well, were subjected to severe thermal degradation for reaction temperatures above 200oC. In general, it can be concluded that the optimum

Figure 1. Influence of the hydrolysis temperature (melt temperature in the ractor) on the mechanical 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-pilot reactor is approximately 2 hours (one hour to reach set temperature).

Both unhydrolyzed and hydrolyzed samples (samples B, C and D) were compounded at the Cadauta plant in Italy using the "Revive" extruder.5 After compounding, 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 using the "Revive" machine. The results obtained on the molded test bars are

Figure 2. The mechanical properties of untreated and treated (formic acid in gas phase, 200oC, 3 h) plastic waste, sample D, containing 30% paper. Sample D without paper: modulus - 1.1 GPa, strength - 17 MPa, elongation at break - exceeding 250%, no break indication at impact testing.

shown in Figure 2 (sample D). The following behavior was observed for both samples C and D:

  • 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 improvements in elongation at break following hydrolysis are illustrated in Figure 3 (unfilled symbols - unhydrolyzed samples; filled symbols - hydrolyzed samples).

20 30 40

CELLULOSE, %

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, 200oC, 3 h).

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.

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.

The strength values are not influenced to a great extent for different paper contents (strength at break approximately 12 MPa), but the E-modulus values increase 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 the hydrolysis 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 because of a high modulus of the fibers (approximately 20 GPa). In general, the results are in an agreement with earlier findings for PP filled with hydrolyzed cellulose.6

Some of the samples compounded on the "Revive" machine were injection-molded in Italy into thin-walled rings from material B, see Figure 4. The results 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).

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