Reprocessingandrestabilizationofgreenhousefilms N.TzankovaDintcheva a ,F.P.LaMantia a, *,R.Scaffaro a ,M.Paci b , D.Acierno c ,G.Camino d a Dipartimento di Ingegneria Chimica dei Processi e dei Materiali, Universita ` di Palermo, Viale delle Scienze, 90128 Palermo, Italy b Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali, Universita ` di Pisa, Via Diotisalvi, 2, 56126 Pisa, Italy c Dipartimento di Ingegneria dei Materiali e della Produzione, Universita ` di Napoli, Piazzale Tecchio, 80, 80125 Naples, Italy d Dipartimento di Chimica Inorganica, Chimica Fisica e Chimica dei Materiali, Universita ` di Torino, Via P. Giuria, 7, 10125 Turin, Italy Received25July2001;accepted26August2001 Abstract Fromtheecologicalandeconomicalpointsofview,reprocessingofpolyethylenegreenhousefilmsisapromisingsolutiontoreduce discardedmaterialsandtoproduceuseful,orpotentiallyuseful,objectsforservice.Filmsexposedoutdoors,however,showinferior mechanicalpropertiesandthemeltprocessingworsenstheseproperties.Theadditionofstabilizersandantioxidantstorecycledplastic productspreventsinherentthermalinstabilitiesfromoccurringwithinthetimeframeofproperprocessing.Inthisstudy,weattemptto explorewaysforimprovingproductperformancebytheadditionoffourdifferentadditiveswhentherecycledfilmsundergointensive shearprocessing.Theprocessisevaluatedbymeasuringthechangesinchemicalstructure(carbonylevolution)aswellasrheologicaland mechanicalcharacteristics(tensileproperties).Theeffectivenessofthevariousadditiveswasestimatedandtheonewiththebestanti- oxidantabilitywasidentified.Theanalysisofprocessingconditionsallowedustofindthatthebestresultsareemphasizedbythecon- tinuousadditionofthestabilizerateachstepofreprocessing. # 2002ElsevierScienceLtd.Allrightsreserved. Keywords: Recycling;Greenhousefilms;Restabilization 1. Introduction PEismainlyusedinagricultureforgreenhousecov- ering,mulchingandpackaging.Therefore,farmsgetrid of a large amount of PE-film wastes which, though being scarcely contaminated by other plastics, contain variable amounts of ground and fertilizer impurities. Tests have confirmed that fertilizers decrease the aging resistance of recycled LDPE. Moreover, plastic repro- cessing becomes more and more difficult with the increaseofthecontentofpollutants;inparticular,fer- tilizersreducetheabsorptionofadditives. Themainproblemsintherecyclingofplasticsaredue to the degradation undergone by the materials during theiruseandrecyclingoperations,and,formixedplas- tics,totheincompatibilityamongthecomponents.The concomitant action of oxygen and UV rays cause the degradation of PE films used as greenhouse coverage. Degradation products decrease the physical and mechanicalpropertiesofthesematerials[1]. Theemploymentofsomeadditiveswhichstabilizethe polymersagainstlight,andmechanicalstressheat,may be useful to prevent degradation phenomena during processing and to extend the lifetime of the materials. Fromapracticalpointofview,stabilizationisgenerally able to grant that the physical properties of the reclaimedmaterialsaresufficientlyclosetothoseofthe virgin ones. For specific applications requiring phenol free stabilization packages, a mixture of hindered aminesandhydroxylaminecanbeused[2–4]. It has been shown [5–9] that, by adding stabilizing systems,likeasuitedmixtureofphosphiteandhindered phenols,thethermalstabilityofsomethermoplasticsis drastically improved and the properties are slightly modifiedevenaftermanyreprocessingsteps.Actingon different species in the degradation cycle, phenols and phosphitesfunctionsynergistically. For the post-consumer polymers, it is important to get knowledge of the degree of degradation undergone during usage. With regard to greenhouse films, the photo-oxidation products due to UV rays exposition must be considered, because they modify the structure and the morphology of PE, with a reduction of the mechanical properties. Moreover, the presence of 0141-3910/02/$-seefrontmatter # 2002ElsevierScienceLtd.Allrightsreserved. PII:S0141-3910(01)00248-8 PolymerDegradationandStability75(2002)459–464 www.elsevier.com/locate/polydegstab * Corresponding author. Tel.: +39-091-656-7203; fax: +39-091- 656-7280. E-mail address: lamantia@dicpm.unipa.it(F.P.LaMantia).