Degradation of Styrenic Plastics During Recycling
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Degradation of Styrenic Plastics During Recycling: Impact of Reprocessing Photodegraded Material on Aspect and Mechanical Properties Charles Signoret, Marie Edo, Dominique Lafon, Anne-Sophie Caro-Bretelle, José-Marie Lopez-Cuesta, Patrick Ienny, Didier Perrin To cite this version: Charles Signoret, Marie Edo, Dominique Lafon, Anne-Sophie Caro-Bretelle, José-Marie Lopez-Cuesta, et al.. Degradation of Styrenic Plastics During Recycling: Impact of Reprocessing Photodegraded Material on Aspect and Mechanical Properties. Journal of Polymers and the Environment, Springer Verlag, 2020, 28, pp.2055-2077. 10.1007/s10924-020-01741-8. hal-02573153 HAL Id: hal-02573153 https://hal.mines-ales.fr/hal-02573153 Submitted on 16 May 2020 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Degradation of Styrenic Plastics During Recycling: Impact of Reprocessing Photodegraded Material on Aspect and Mechanical Properties Charles Signoret1 · Marie Edo1 · Dominique Lafon3 · Anne‑Sophie Caro‑Bretelle2 · José‑Marie Lopez‑Cuesta1 · Patrick Ienny2 · Didier Perrin1 Abstract The major technical limitations in polymer recycling are their incompatibility between each other and their ageing. In this study, impact reinforced styrenics, namely HIPS and ABS, were evaluated in the scope of their alterations through recycling photooxidized material. In this purpose, plates were photodegraded in both natural and accelerated conditions. FTIR-ATR was used to monitor their ageing. After the desired ageing durations, plates were ground, extruded and injected into ISO1 dumbbell tensile test specimens to simulate recycling of degraded polymers. Strong interactions were observed between pho- tooxidation and polymer processing through photometry measures, associated color changes, tensile and impact properties. It was noticed that unaged materials displayed only moderated alterations through recycling. Because of their close chemistry, HIPS and ABS share several modifcations but ABS was less altered and mainly impact properties were afected. HIPS and ABS diference of sensibilities could be rooted in PB phases diferent morphologies and grafting between the two materials. Keywords Polymer recycling · WEEE · Styrenics · Colorimetry · Mechanical properties · FTIR Abbreviations PB Polybutadiene ABS Acrylonitrile butadiene styrene PS Polystyrene Aext Reextruded samples from accelerated SAN Styrene acrylonitrile ageing V Virgin samples AN Acrylonitrile Vext Reextruded unaged samples ASA Acrylonitrile styrene acrylic rubber UV Ultraviolet ATR Attenuated total refection WEEE or W3E Waste of electrical and electronic CRI Color Rendering Index equipment CRT Cathodic ray tube WEEP WEEE plastics FTIR Fourier transform infrared GPPS General purpose polystyrene HIPS High impact polystyrene Introduction LED Light-emitting diodes Next Reextruded samples from natural ageing Waste of electric and electrical equipment (WEEE) genera- NIR-HSI Near-infrared hyperspectral imagery tion is rapidly increasing with the constant worldwide rise of Gross Domestic Products [1], especially in populated * developing countries as India or China, tending to meet Didier Perrin unsustainable models which, by excessive goods consump- [email protected] tion, energy production and waste generation, deplete and 1 Polymers Composites and Hybrids (PCH), IMT Mines Ales, pollute the environment more than it can sustain durably for Alès, France our population density. These lifestyles are largely found in 2 LMGC, IMT Mines Ales, Univ Montpellier, CNRS, Alès, occidental countries [2], which themselves have disposed a France great part of their WEEE in aforementioned countries [3, 3 Euromov Montpellier, IMT Mines Ales, CNRS, Alès, France 4]. These objects lifespans are also decreasing, with high renewal rates, even if they are still functional [5, 6]. Reuse, ABS, with a more complex morphology with matrix inclu- repairing/remanufacturing are advised but not sufciently sions [30]. This is due to the respectively preferred synthesis applied [7–9]. Also, black color generalized among WEEE route for each material [31–34]. HIPS is generally synthe- plastics (WEEP), especially for professional computers cas- sized through bulk copolymerization, where the pre-rubber ing or telephones, as shown on Fig. 1. Carbon black limits phase is solubilized in styrene monomer before polymeriza- polymer ageing by absorbing UV-rays, even if this phe- tion. This leads to multimodal size distribution and inclu- nomenon can be only delayed and slowed down [10, 11]. sions of polystyrene domains within nodules. Emulsion This surface ageing, mainly by photo-oxidation, is often grafting, the main synthesis route for ABS, consists of a characterized by an infamously yellowing [12] as seen on frst step of emulsion polymerization and crosslinking of the 1990s telephone station of Fig. 1. Interestingly enough, polybutadiene nodules which are then grafted during the plastic retained a white color where the handset and sta- matrix polymerization. This enables narrower and way fner tion meet, as it was unexposed to the sun and thus avoided rubber particles distribution. These preferences in synthesis photooxidation. However, polymers tainted in mass with routes are justifed as impact improvement is optimal for carbon black become invisible to near-infrared hyperspec- 1–3 µm PB nodules in HIPS but 0.05–0.50 µm in ABS [31]. tral imagery (NIR-HSI), the currently most used technology Also, ABS contains generally more PB than HIPS as PB with sink-foat for industrial sorting [13, 14], mandatory to rates are reported from 5 to 30 w% for ABS [35] but usually obtain satisfactory properties through mechanical recycling from 6 to 8.5 w% for HIPS and up to 15 w% at maximum [15, 16]. Development of new technologies to overcome this [36]. dark plastics sorting issue is currently subject to tremendous Even if PB enables very interesting impact properties, research [17–24] and could enable proper recycling of sorted it often forbids transparency, slightly lowers the Young WEEP. Study of styrenics recyclability, especially after age- modulus and can initiate degradation. Indeed, several stud- ing, is thus a hot topic. ies showed that because of its reactivity, PB could be easily Nowadays, the main WEEP are styrenics: namely high oxidized with temperature or ultraviolet (UV) rays [37, 38]. impact polystyrene (HIPS) and acrylonitrile–butadiene–sty- ASA (acrylonitrile styrene acrylic) is an alternative solu- rene (ABS) and their respective blends with PPE (polyphe- tion, often applied for outdoor applications, where PB is nylene ether) and PC (polycarbonate) [25–27]. HIPS and substituted by acrylic rubber, less sensitive to ageing due to ABS represent together 55 w% of WEEP according to Maris its lack of double bonds [39]. However, because of its price et al. [25], and 80 w% according to Stenvall et al. [28]. HIPS and lower impact properties, ASA is not widely spread. and ABS consist of a rigid thermoplastic matrix, respec- Styrenics thermo- and photo-oxidations were thus subject tively polystyrene (PS or GPPS for General Purpose) and the to important research. As soon as 1968, Shimada et Kabuki statistical copolymer styrene-acrylonitrile (SAN), in which [37] demonstrated that weathering of ABS mainly occurred were incorporated slightly cross-linked polybutadiene (PB) by PB photooxidation. Davis et Gordon [40] found that nodules, which dramatically enhance their impact proper- pigmentation could strongly interfere with ageing as wave- ties [29]. Nodules are generally coarser within HIPS than in lengths between 295 and 340 nm were the more impacting. Fig. 1 Example of black coloration generalization for small WEEE plastics—note tint difference between exposed and preserved areas of the 1990s phone station Contribution to degradation then strongly decreases with contaminations. To evaluate possible interactions between the wavelength. Jouan et Gardette [12, 41] used chemical photo-ageing and recycling, La Mantia et Gardette [49] titration and derivation to diferentiate the diferent oxidized reprocessed photo-oxidized LDPE flms and found that species that occurs during ageing. Notably, they highlighted it permitted partial regeneration of properties that they conjugated species, involving aromatic cycles and newly attributed to homogenization and dilution of defects. Soc- formed vinyls and carbonyls (Fig. 2), which are a source of calingame et al. [50, 51] studied the reprocessing of natu- discoloration. Thanks to this methodology, Gardette et al. rally and artifcially weathered wood four reinforced PP [42] also proposed multiple degradation mechanisms to PS, and also highlighted a similar “regeneration” mechanism SAN, HIPS and ABS. They emphasized the initiator role and added that shorter chains formed during photodegra- of PB in both HIPS and ABS. Finally, they highlighted that dation could recrystallize thanks to recycling. Pfaender ageing within SAN and PS generates chain scissions and and his collaborators [52–57] substantially published on conjugated compounds whereas