Furthermore, the PET flakes are exposed to a melting temperature in the in- jection barrel which would degrade most organic substances in the middle layer. In a new multilayer PET bottle, this middle layer is shielded by layers made of virgin PET. The contents of the bottle(food)are therefore separated by a layer of virgin PET from the middle layer. In the case of inorganic toxic substances which might have migrated into the PET surfaces in the ppb-range and furthermore survived the processing tem- peratures, these extremely small fractions will be diluted with the melt cake in the injection barrel and hot runner system. CONCLUSIONS • Pressure from environmentalists and legislations require creative solu- tions for re-using of packages. Discarded plastic packages can be repro- cessed into articles similar to the originals. • Co-injection technology, allowing for the injection of a layer of melt of reground PET flakes into the center of the preform wall, offers a technology of using low cost post-consumer regrind PET bottle resin. • The layer of the melt of reground PET flakes is completely insulated in the middle of the bottle and therefore has no contact with the filled-in product such as food, nor with an outside environment. Contamination of filled-in products is therefore excluded. • Cost savings by this method are about 20%. 26 PET Co-injection Molding Recycling of Post-consumer Greenhouse Polyethylene Films: Blends with Polyamide 6 F. P. La Mantia and D. Curto Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Universitá di Palermo, Viale delle Scienze, 90128 Palermo, Italy INTRODUCTION Problems connected with recycling of polymeric materials arise mainly from the heterogeneous nature of plastics waste and from degradation of polymers occuring either during their processing or their lifetime. As for the first point, important only when mixtures of plastics have to be recy- cled, it is well established that a strong incompatibility is typical for polymers usually found in plastics wastes (PE, PET, PVC, PS, PP). This incompatibility gives rise to materials which are very difficult to process and/or have inferior mechanical properties. Regarding the degradation experienced by polymeric materials, the formation of lower molecular weight fractions, possible presence of crosslinking, and oxygenated groups can further worsen properties of the re- cycled materials. Polyethylenes are the most popular polymers and as such are the most fre- quently recycled. In particular, films from greenhouses, although highly de- graded by UV radiation, are recycled by means of well-established processes, leading to materials frequently used to manufacture films and molded products with low mechanical properties. Even more important problems in the recycling of greenhouse films arise from the presence of products of photooxidation, which modify both structure and morphology of polyethylene, strongly affecting its mechanical properties. 1-5 Es- pecially, the presence of low molecular weight chains and of oxygenated groups affects the properties of a recycled material. In previous works, 6,7 a possibility of use of photooxidized polyethylene in blends with nylon 6, to improve blend compatibility, was demonstrated. F.P. La Mantia and D. Curto 27 In this paper, after a short review of the method, the properties and morphol- ogy of blends and coextruded films made out nylon 6 and recycled photooxidized polyethylene will be presented. State of Art Blends of polyamides and polyolefines are potentially very interesting, but, be- cause of the strong incompatibility of both polymers, the product of blending usually has poor properties. Many efforts have been devoted to compatibilize these blends. 8-12 Most of the methods consider functionalized polyolefines which can react with the amino groups of polyamides, giving rise to copolymers, stabi- lizing the blend. Such functionalization, in general a long and expensive step, is mostly performed by chemical modification of the polyolefine structure. In a previous study, 6 we have demonstrated that photooxidized polyethylene offer similar results. A low density polyethylene sample with different degree of photooxidation (see Table 1) was blended with nylon 6 (LDPE 25 wt%). The results of the Molau test are shown in Figure 1. The solution is clear in the case of blend PEPh0/Ny. The solution consists of nylon 6, which is soluble in formic acid. The upper part of the same test tube is a suspension of polyethylene particles. The tests regarding blends containing photooxidized polyethylenes show, on the contrary, an in- creasing and persistent turbiditywhichrepresentsasuspension of colloidal par- ticles. 28 Greenhouse PE Film Recycling by Blending with PA Table 1 Physico-chemical properties of polyethylene samples Sample code Photooxidation time* MFI Gel C=O (h) (g/10 min) (%) (mol ⋅ L -1 ) PEPh0 0 0.08 0 0 PEPh24 24 - 11 0.07 PEPh48 48 - 19 0.11 PEPh72 72 - 25 0.28 * photooxidation was carried out using eight UVB fluorescent lamps for 24, 48, and 72 h. The cycle adopted was: 8 h UV radiation atT=60 o C and 4 h condnesation atT=50 o C Following Molau and other authors, 11-13 the presence of colloidal suspension is attributable to the existence of LDPE/Ny 6 graft copolymers, act- ing as interfacial agents. In our case, we believe that a chemical reaction between carbonyl groups (formed during photooxidation of polyethylene) and amino groups of nylon 6 occurred during melt blending. The suspension turbidity increases along with an increase in the photooxidation time of polyeth- ylene, and it isalso parallelto the concentration of carbonyl groups. The SEM micrographs of samples of blends con- taining virgin and the most extensively photooxidized polyethylene (Figures 2 and 3) con- firm such an interpretation. In the blend contain- ing virgin polyethylene, the polyamide forms the continuous phase and the polyethylene the dis- crete phase. The polyethylene particles have aver- age dimensions ranging from 5 to 10 µ m. The F.P. La Mantia and D. Curto 29 Figure 1. Molau test. From left to right: PEPh0/Ny; PEPh24/Ny; PEPh48/Ny and PEPh72/Ny. Figure 2. SEM micrograph: PEPh0/Ny. Figure 3. SEM micrograph: PEPh72/Ny. micrographs of blends containing photooxidized polyethylenes show an almost homogeneous phase and are hardly distinguishable as a result of good dispersibility. Elastic modulus, tensile strength and elongation at break are reported in Figure 4. Tensile strength and elastic modulus increase with an increase in the photooxidation time, whereas the elongation at break increases as the photooxidation time increases until it begins to decrease again, which occurs af- ter 50 h of photooxidation. The elongation decrease, as will be explained in the following, can be attributed to a very low value of the elongation at break of a more extensively photooxidized polyethylene. The SEM micrographs and the results of the mechanical properties are consis- tent with the proposed chemical reactions between carbonyl groups and amino end-groups forming a graft copolymer. This copolymer acts as interfacial agent between continuous and dispersed phases. The presence of such an interfacial agent causes smaller dimensions of the dispersed particles and a good adhesion between discrete and continuous phases. These results suggest the possibility of using degraded (photooxidized) poly- ethylene, from recycling of films for greenhouses, as a functionalized polymer to obtain compatibilized nylon/polyethylene blends. 30 Greenhouse PE Film Recycling by Blending with PA Figure 4. Mechanicalpropertiesofblends.PEPh0/Ny, PEPh24/Ny, PEPh48/Ny,andPEPh72/Ny. EXPERIMENTAL Materials The materials used in this work were: virgin polyethylene (V), nylon 6 (Ny), and two samples of recycled polyethylene (R1 and R2). These latter materials were obtained from films for greenhouses which were photooxidized to a great extent. The main physico-chemical properties of the raw materials are reported in Table 2. The blends were prepared by melt extrusion in a Brabender laboratory sin- gle-screw extruder (D = 19 mm, L/D = 25) at 100 rpm with a die temperature of 260 o C. The R2/Ny blend was also prepared by melt mixing of homopolymers in the same Brabender Plasticorder equippedwith amixer headmodel W50 EHat 260 o C and 100 rpm for 15 min. The mixing time was sufficient to attain a practi- cally constant value of torque. Homopolymers were subjected to the same treat- ment. All blends were prepared with 80 wt% of nylon 6. For comparison, a blend with 20% of nylon 6 was also prepared. Coextruded films were manufactured by using two layers coextruder Toyplast (Crespi, Italy) with a blowing unit. The coextruder was operated at a flow rate of about 20 kg/h. The thickness of the nylon layer was adjusted by the extruder rate, maintaining a layer ratio of about 4. The die temperature was 215 o C for all the runs. Runs were carried out with an axial draw ratio of 50 and a blow up ratio of 2 for all the blends. F.P. La Mantia and D. Curto 31 Table 2 Raw materials Sample Supplier M w M w /M n Gel % V Enichem Polimeri 250,000 7.2 0 R1 - - - 40 R2 - - - 56 Ny Snia 37,000 2.1 - Structural studies The gel content of two samples of recycled polyethylene was determined by means of a Soxhlet extractor. Approximately 0.3 g of any photooxidized polyeth- ylene sample was extracted by refluxing p-xylene close to its boiling point for 48 h. Samples of all blends, fractured under liquid nitrogen, were observed, using a scanning electron microscope, Philips Model 505. The surface of the specimens was coated with gold. Molau tests 11 were carried out by dissolving 200 mg of sample in 10 mL of 80 % formic acid. Mechanical properties Tensile properties and peel adhesion were determined, using an Instron ma- chine Model 1122 at room temperature. A crosshead speed of 5 cm/min and a gauge length of 3 cm were used to obtain the stress-strain curves. The specimens used for tensile tests were cut out of sheets obtained by com- pression molding atT=240 o C (180 o C for the purepolyethylene). All the reported results are an average of at least 10 measurements. Impact strength was determined at room temperature on notched samples us- ing a Fractoscope (CEAST) in an Izod mode. Ball drop measurements were car- ried out using a Ceast apparatus. Before testing, the specimens were equilibrated in ambientconditions (T = 20 o C and 60%R.H.) for at least3 days. RESULTS AND DISCUSSION Blends Figure 5 shows the results of the Molau tests of the following blends: V/Ny, R1/Ny, and R2/Ny prepared by extrusion. The solution is clear for the blend V/Ny, consisting of nylon 6 dissolved in formic acid. The upper part is a suspen- sion of polyethylene particles. The tests of blends containing recycled photooxidized polyethylene show a turbidity which is due to a suspension of col- loidal particles. As already pointed out, this colloidal suspension is caused by the presence of polyethylene/nylon graft copolymers formed during melt extru- sion in chemical reaction between carbonyl groups of the recycled photooxidized polyethylene and amino groups of nylon 6. 32 Greenhouse PE Film Recycling by Blending with PA also increases. The R2 sample has a larger amount of C=O groups and thus its blend shows a more intense turbidity. The results of Molau test of R2/Ny blend, prepared by extrusion and melt mixing, are reported in Figure 6. The blend pre- pared by melt mixing shows a more intense turbidity. The influence of a composition was tested for blend, having 80 wt% polyethyl- ene. The Molau test (Figure 6) shows that at the low content of nylon, no turbid- ity is observed. F.P. La Mantia and D. Curto 33 Figure 5. Molau test. From left to right: V/Ny, R1/Ny, R2/Ny prepared by melt ex- trusion. Figure 6. Molau test. From left to right: R2/Ny by melt extrusion, R2/Ny (Ny = 20%), and R2/Ny by melt mixing. As the degradation degree of the polyethylene rises, the suspension turbidity sion ranging from 5 to 30 µ m. Furthermore, a negligible adhesion between the two phases is observed. The micrographs of the samples with recycled PE show that the dimensions of the discrete phase decreases with an increase in the degradation degree of the polyolefines (Figures 7b and c) and with severity of the mixing process (mixing vs. extrusion) (Figures 7c and d). Moreover, the adhesion improves with the 34 Greenhouse PE Film Recycling by Blending with PA Figure 7. SEM micrographs: (a) V/Ny, (b) R1/Ny, (c) R2/Ny, prepared by extrusion, (d) R2/Ny pre- pared by melt mixing. The SEM micrographs of the same samples are givenin Figure 7a-d. The blend containing virgin PE (Figure 7a) has polyethylene particles of average dimen- same trend. In particular, the blend with R2 prepared by melt mixing (Figure 7d) shows an almost homogeneous phase. All the above results indicate that the formation of graft copolymers increases with: • the photooxidation degree of the polyethylene • the content of nylon • the intensity of the mixing. The presence of graft copolymers, acting as reinforcing interphase between the two polymers, improves some mechanical properties of these blends, compared with blends which were not compatibilized. Modulus, E, tensile strength, TS, elongation at break, EB, and impact strength, IS, for all blends are reported in Table 3. Modulus and impact strength can be increased by the use of recycled degraded polyethylene and, for blends with the same components, by increasing the mix- ing intensity (mixer vs. extruder). F.P. La Mantia and D. Curto 35 Table 3 Mechanical properties of polyethylene/nylon blends Sample E (MPa) TS (MPa) EB (%) IS (J/m) V/Ny 700 30 140 110 R1/Ny (extr) 800 25 30 120 R2/Ny (extr) 1000 30 10 125 R2/Ny (mix) 1200 46 25 135 Table 4 Elongation at break of polyethylene samples Sample EB (%) V 490 R1 180 R2 110 [...]... physical characteristics of homopolymers and compositions of the studied mixtures Polymer Trade name MFI Density 3 Mixture (g/10 min) (g/cm ) 1 2 3 4 LDPE Riblene CF 2200 2 0.917 70 63 49 42 LDPE Riblene EF 2200 0.7 0.917 20 18 14 12 HDPE Eraclene H ZB 5515 0 .3 0.9 63 10 9 7 6 PP Moplen X 30 5 7.5 0.895 - 8 24 32 PS BASF Polystirol 454C 1. 53 1.0 03 - 2 6 8 Table 2 Blends of the plastic fractions from urban... represent the large majority of polymers in the plastic wastes, some of the above works were specifically focussed on the 1 ,3- 5 wastes In this study we will report results concerning a wide analysis of: • • • quaternary blends of virgin LDPE/HDPE/PP/PS, in which LDPE is the major component, as in the plastic wastes a light fraction from the urban solid wastes 13, 14 a blend of HDPE with the heavy fraction... Ragosta, Polymer, 27, 1874 (1986) G E Molau, J Polym Sci., A3, 1267 (1965); Kolloid Z.Z Polym, 238 , 4 93 (1970) G Illing in Polymer Blends: Processing Morphology and Properties, Eds., E Martuscelli, R Palumbo and Kryszewski, Eds., New York, 167 (1980) H K Chuang and C D Han, J Appl Polym Sci., 30 , 165 (1985) E Gattiglia et al 39 Recycling of Plastics from Urban Solid Wastes: Comparison Between Blends... Corso Europa 30 , 16 132 Genova, Italy * Enichem Polimeri, Centro Tecnologico, Via Iannozzi 1, 20192 S Donato Milanese (Mi), Italy INTRODUCTION The recycling of plastic wastes is not a recent problem for plastic users and producers Since long, industrial scraps are recycled within the production cycle itself or recovered as lower grade materials and refabricated into new products On the contrary, plastics... crosshead speed of 5 mm/min according to ASTM D 638 The flexural modulus was measured in an Arquati Dynamometer AG7E at a speed of 100 mm/min and a distance of 50.8 mm according to ASTM D790 All results are average of at least 10 measurements The IZOD impact tests were performed aco o cording to ASTM D256 on a CEAST pendulum model 6545/000 at T = 30 C, 0 C o and 23 C The last results are average of 15-20 measurements... exploited in the future The major problem still facing the viable recycle of plastic wastes is their chemical multiplicity: several different polymers are present in plastic wastes and many of them are mutually incompatible, making the reprocessing of them, as a whole, practically impossible On the other hand, the separation of the individual plastics is extremely expensive and must consequently be simplified... Such heterogeneous mixtures are often scarcely compatible, giving rise to processability and quality problems 40 Recycling of Plastics from Urban Solid Wastes By using the flotation method, generally two fractions are obtained from the plastic wastes: a light fraction, floating on water, and a heavy fraction (density 3 >1 g/cm ) The first fraction is essentially made of low and high density poly(ethylene)... Radiat Phys Chem., 23, 699 (1984) F P La Mantia, Eur Polym J., 20, 10 (1984) 38 6 7 8 9 10 11 12 13 Greenhouse PE Film Recycling by Blending with PA D Curto, A Valenza, and F P La Mantia, J Appl Polym Sci., 39 , 865 (1990) F P La Mantia and D Curto, Polym Deg Stab., 36 , 131 (1992) F Ide and A Hasegawa, J Appl Polym Sci., 18, 9 63 (1974) S Cimmino, L D’Orazio, R Greco, G Maglio, M Malinconico, C Mancarella,.. .36 Greenhouse PE Film Recycling by Blending with PA Table 5 Mechanical properties of compatibilized PE/Ny blends Sample E (MPa) TS (MPa) EB (%) IS (J/m) FPE/Ny* 79 52 40 70 R2/Ny (mix) 120 46 25 135 *FPE - functionalized polyethylene (taken from Ref. 13) Table 6 Mechanical properties of coextruded films TS (MPa) EB (%) BD (cN) Peeling (cN/m) 450 105 80 440 165 900 draw transv draw transv V/Ny 31 ... according to ASTM D3 835 in a gas pressure o viscometer at T = 190 C Die of diameter 0.5 mm and L/D ratio of 10 was used The melting flow index, MFI, was determined according to ASTM D 1 238 /c in a Karl Frank model 736 94 Density The homopolymer and blend densities were measured using a gradient column filled with water and isopropyl alcohol in such a proportion as to obtain a density 3 range from 1.000 . 20 18 14 12 HDPE Eraclene H ZB 5515 0 .3 0.9 63 10 9 7 6 PP Moplen X 30 5 7.5 0.895 - 8 24 32 PS BASF Polystirol 454C 1. 53 1.0 03 - 2 6 8 Table 2 Blends of the plastic fractions from urban solid wastes Polymer Composition. Eds., New York, 167 (1980). 13. H. K. Chuang and C. D. Han, J. Appl. Polym. Sci., 30 , 165 (1985). 38 Greenhouse PE Film Recycling by Blending with PA Recycling of Plastics from Urban Solid Wastes: Comparison. - - - 56 Ny Snia 37 ,000 2.1 - Structural studies The gel content of two samples of recycled polyethylene was determined by means of a Soxhlet extractor. Approximately 0 .3 g of any photooxidized