Valorisation of pyrolytic tyre char as filler in polypropylene

Saul, Cleopatra Lerato (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Pyrolytic tyre char (PT-char) produced during waste tyre pyrolysis is conventionally perceived as a waste stream due to its high amounts of impurities. The aim of this research study is to investigate and analyse the feasibility of PT-char as filler in order to enhance the mechanical properties and degradation stability of polypropyelen (PP) composites. In the present study, the untreated PT-char was first demineralised with acid-base lixiviants (nitric acid and sodium hydroxide) to remove impurities. The impurity removal step was followed by surface modification using 3-methacryloxypropyletrimethoxysilane (3-MPTS) and titanium IV 2,2 (bis-2-propenolatomethyl) butanolato, tris (dioctyl) pyrophosphato-O (LICA 12) coupling agents and maleic anhydride-grafted polypropylene (MAgPP) compatibiliser to improve the filler reactivity towards the polymer. PP composites filled with various amounts of unmodified and modified PT-char were produced and tested for mechanical properties and degradation stability. The untreated PT-char and the demineralised PT-char were characterised in terms of their particle size, surface area, proximate and ultimate analysis and surface functional groups. Demineralisation reduced the ash content from 16.5 wt.% to 2.70 wt.%, average particle size decreased significantly from 89.9 μm to 11.0 μm and the surface area increased slightly from 73.9 m2/g to 76.7 m2/g. Functional groups such as carbonyl, carboxylic and hydroxyl groupswere present on the surface of the untreated PT-char before any treatment. Silanol group which belong to the silane was present on the modified PT-char. However, phosphate group which belong to titanate could not be verified on the modified PT-char since it appear on the unmodified PT-char. Incorporation of PT-char increased the mixing torque of PP composites melt due to rigid particles of PT-char, which limit the movement of PP chains. The mixing torque of PP composites increased with an increase in PP-char loading. Surface modification enhanced the interface between PT-char and the PP matrix by reducing the mixing torque. Incorporation of unmodified PT-char did result in some improvements in some mechanical properties such as tensile strength and elongation at break of PP composites, due to its heterogeneous spherical particle shape which gave uniform distribution of stress. On the other hand, demineralisation of PT-char reduced the mechanical properties. This was due to reduction in minerals compounds contained within PT-char which are beneficial for mechanical properties of PP composites. PT-char loading higher than 1.94 wt.% reduced the mechanical properties of PP composites, particularly with demineralised PT-char. This was due to the aggregation tendency of small particle sizes which caused defects in the composites system. Surface modification with silane and titanate coupling agents improved the mechanical properties of PP composites due to the enhancement of the interface between PT-char and the PP matrix. However, the performance of MAgPP compatibiliser was very poor due to an insufficient esterification process between the anhydride groups of the MAgPP and the hydroxyl groups of the PT-char. Thermal and photo-oxidative degradation studies revealed that demineralised PT-char is less pro-degradant than untreated PT-char due to lower transition metal content in its surface. Higher PT-char loadings (0.77 wt.% and 1.94 wt.) accelerated thermal and photo-oxidative degradation, particularly with demineralised PT-char regardless of surface modification. This was due to aggregation tendency of PT-char particles which caused defects in the composites system. Surface modification with 3-MPTS and LICA 12 leads to significant improvements in the thermal and photo-oxidative degradation stability of PP composites particularly at lower PT-char loading (0.38 wt.%), due to an enhanced interface between PP and the PT-char. However, MAgPP compatibiliser accelerated the thermal-oxidative degradation of PP composites due to thermo-responsive groups, such as carboxylic acids, which originate from partial hydrolysis of maleic anhydride. Keywords: Waste tyre, PT-char, composites, surface modification

AFRIKAANSE OPSOMMING: Pirolitiese bandverkoolsel (PT-char) geproduseer tydens pirolise van afvalbande word konvensioneel beskou as ʼn afvalstroom as gevolg van die hoë hoeveelhede onsuiwerhede. Die doel van hierdie navorsingstudie is om die lewensvatbaarheid van PT-char as vuller te ondersoek en analiseer om die meganiese eienskappe en degradasie stabiliteit van polipropileen samestellings te verhoog. In die huidige studie is onbehandelde PT-char eers gedeminiraliseer met suurbasis loogmiddels (salpetersuur en natriumhidroksied) om onsuiwerhede te verwyder. Die stap om onsuiwerhede te verwyder is gevolg deur oppervlak modifikasie deur 3- metakrieloksiepropieletrimetoksiesilaan (3-MPTS) en titanium IV 2,2 (bis-2-propenolatometiel) butanolato, tris(dioktiel)pirofosfaato-O (LICA 12) koppelingsagente te gebruik, en maleïensuuranhidried-geënte polipropileen (MAgPP) verbinder om die vuller reaktiwiteit na die polimeer te verbeter. PP-samestellings gevul met verskeie hoeveelhede ongemodifiseerde en gemodifiseerde PT-char is geproduseer en getoets vir meganiese eienskappe en degradasie stabiliteit. Die onbehandelde en gedeminiraliseerde PT-char is gekarakteriseer in terme van hul partikelgrootte, oppervlakarea, naaste- en eindanalise en oppervlak funksionele groepe. Demineralisering verminder die asinhoud van 16.5 gew.% Tot 2.70 gew.%, Gemiddelde deeltjiegrootte het aansienlik afgeneem van 89.9 μm tot 11.0 μm en die oppervlakte het effens toegeneem van 73.9 m2/g tot 76.7 m2/g. Funksionele groepe soos karboniel-, karboksiel- en hidroksielgroepe was teenwoordig op die oppervlak van die onbehandelde PT-char voor enige behandeling. Silanol-groep wat aan die silaan behoort, was teenwoordig op die gewysigde PT-char. Fosfaatgroepe wat aan titanaat behoort, kon egter nie op die gewysigde PT-char geverifieer word nie, aangesien dit op die ongemodifiseerde PT-char verskyn. Inkorporasie van PT-char het die menging wringkrag van PP-samestellingsmeltsel verhoog as gevolg van rigiede partikels van PT-char, wat die beweging van PP-kettings beperk. Die menging wringkrag van PP-samestellings verhoog met ʼn verhoging in PT-char-lading. Oppervlak modifikasie versterk die tussenvlak tussen PT-char en die PP-matriks deur die menging wringkrag te verminder. Inkorporasie van ongemodifiseerde PT-char het tot sommige verbeteringe in sommige meganiese eienskappe gelei soos treksterkte en verlenging van die breek as gevolg van sy heterogene sferiese partikel vorm wat tot uniforme verspreiding van spanning lei. Aan die ander kant het die demineralisering van PT-char die meganiese eienskappe verminder. Dit was te danke aan die vermindering in minerale verbindings wat in PT-char bevat is, wat voordelig is vir meganiese eienskappe. PT-char lading hoër as 1,94 gew.% het die meganiese eienskappe van PP-samestellings verminder, veral met gedeminiraliseerde PT-char. Dit was as gevolg van die aggregasie geneigdheid van klein partikelgroottes wat defekte in die samestellingsisteem veroorsaak het. Oppervlak modifikasie met silaan- en titanietkoppelingsagente het die meganiese eienskappe verbeter as gevolg van die verterking van die tussenvlak tussen PT-char en die PP-matriks. Die doeltreffendheid van MAgPP-verbinder was egter baie swak as gevolg van ʼn onvoldoende esterifikasieproses tussen die anhidriedgroepe van die MAgPP en die hidroksielgroepe van die PT-char. Termiese en foto-oksidatiewe degradasiestudies het bekend gemaak dat gedeminiraliseerde PT-char minder pro-degradent as onbehandelde PT-char is as gevolg van laer oorgangmetaalinhoud in sy oppervlakte. Hoër PT-char-lading (0.77 gew.% and 1.94 gew.%) het termiese en foto-oksidatiewe degradasie versnel, veral met demineralisasie ongeag van oppervlak modifikasie. Dit was te danke aan die versamelingstendens van PT-char deeltjies wat defekte in die samestellingsstelsel veroorsaak het. Oppervlak modifikasie met 3-MPTS en LICA 12 lei tot beduidende verbeteringe in die termiese en foto-oksidatiewe degradasie stabiliteit van PP-samestelling, veral by laer PT-char-lading (0,38 gew.%), as gevolg van ʼn versterkte tussenvlak tussen PP en die PT-char. MAgPP-verbinder het die termiese-oksidatiewe degradasie van PP-samestelling egter versnel as gevolg van termo-responsiewe groepe, soos karboksielsure, wat ontstaan uit gedeeltelike hidrolise van maleïensuuranhidried. Sleutelwoorde: Afvalbande, PT-char, samestellings, oppervlak modifikasie

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