Sustainable Alternative Composites Using Waste Vegetable Oil Based Resins
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Journal of Polymers and the Environment https://doi.org/10.1007/s10924-019-01534-8 ORIGINAL PAPER Sustainable Alternative Composites Using Waste Vegetable Oil Based Resins Felipe C. Fernandes1 · Kerry Kirwan1 · Peter R. Wilson1 · Stuart R. Coles1 © The Author(s) 2019 Abstract Laminates were produced with epoxy resins from waste vegetable oil (WVO) intended for the manufacturing of environ- mentally-friendly alternatives for the composites industry. Post-use cooking oil appears a promising source of triglycerides for polymer manufacturing. Matrices cured with methylhexahydrophthalic anhydride (MHHPA) were reinforced with glass and fax fbres, creating a library of composites that were compared to analogues from virgin oil and benchmarked against commercial diglycidyl ether of bisphenol A (DGEBA). Glass fbre-reinforced composites presented Young’s moduli similar to the benchmark but reduced tensile strength. Chemical pre-treatment of the fax fbre (NaOH and stearic acid) countered the limited tensile performance observed for materials with untreated fax; improvements were evidenced by DMA and SEM. Moreover, WVO-based resins greatly improved impact properties and reduced density with no efect on thermal stability. Therefore, WVO-based composites appear as more sustainable alternatives in applications demanding toughness, stifness and lightweight over strength. Keywords Biocomposites · Natural fbres · Thermosetting resins · Mechanical testing Introduction in carbon footprint, but also presents challenges regard- ing eco- and human toxicity [10]. For example, diglycidyl Natural fbre-reinforced composites (NFRC) have gained ether of bisphenol A (DGEBA), a molecule predominantly attention in industry and academia in recent decades as an used in the epoxy resin market, uses bisphenol A (BPA) as environmentally-friendly alternatives for traditional com- a precursor [11]. This molecule is a recognised teratogenic posites produced with glass fbres (GFRC) [1]. Vegetable agent, endocrine disruptor, presents long lasting efects to fbres have been rediscovered as reinforcing agents and aquatic life, and has been removed from polymers used in extensively investigated in applications with thermoplastic baby bottles [12–14]. Specifcally, bisphenol-based networks and thermoset matrices [2]. They present advantages over such as those formed with DGEBA can release BPA even traditional fbres such as reduced density, price, renewabil- after curing since these cross-linked units are susceptible to ity, biodegradability, and lower environmental burdens [3]. hydrolysis [11]. Consequently, NFRC have demonstrated their successful Increasing environmental concerns, tighter legislation and applicability in a number of segments, ranging from auto- awareness about the toxicity of these resins have driven stake- motive sector (both in interior and exterior applications), holders to seek more sustainable alternatives for the thermoset construction, design and packaging industry [4–8]. composite market [15, 16]. In this regard, the community has Nevertheless, the utilisation of petroleum-derived res- explored the production of thermoset matrices from environ- ins for the production of composite laminates reduces the mentally-friendly resins as a strategy to reduce the manufac- overall environmental benefts of using NFRC [9]. The use turing impacts [17–19]. Amongst diferent candidates, veg- of these resins not only restricts the potential reductions etable oils (VOs) have been considered as a key platform to enable a shift towards a greener polymer industry due features * Stuart R. Coles such as price, availability, safety and chemical versatility [20]. [email protected] The main chemical constituent of VOs, triglycerides, can be manipulated with ease to produce resins with diferent func- 1 WMG, University of Warwick, Gibbet Hill Road, tionalities such as epoxy, maleic and acrylated resins, therefore Coventry CV4 7AL, UK Vol.:(0123456789)1 3 Journal of Polymers and the Environment enabling a wide range of applications [21–24]. Consequently, vegetable oil (same blend) were collected from a food out- VO-based resins have successfully demonstrated in the prepa- let at the University of Warwick, Coventry, UK. Hydrogen ration of biocomposites reinforced with vegetable fbres such peroxide (30% v/v), toluene (puriss. p.a. > 99.7%), dichlo- as hemp [25, 26], fax [27, 28], kenaf, switchgrass [29], wheat romethane (puriss. 99%), methyl-hexahydrophtalic anhy- straw and recycled paper [27]. These approaches manufactured dride (MHHPA, 96%, mixture of isomers cis and trans) composites combining competitive mechanical properties with and 2-methylimidazole (2-MI, 99%) were supplied by increased bio-based content. Most importantly, these materials Sigma-Aldrich UK. Stearic acid, ethanol, MgSO4 (dried), proved to be able to deliver extra properties such as biodegra- NaHCO3 and NaOH were supplied by VWR International. dability and improved impact performance in comparison to All chemicals, with the exception of the WVO, were used as traditional resins [30, 31]. received. Flax fbres (Biotex Flax Fiber 2/2 Twill 200 GSM) The production of polymeric networks from waste vegeta- and Glass fbres (Woven Glass 2/2 Twill 280 GSM) were ble oil (WVO) ofers opportunity for the production of a next supplied by Easy Composites Ltd, UK. Bio-based epoxy generation of bio-based materials based on the waste valori- resins were synthesised from purifed waste vegetable oil sation principle [32]. The exploration of this post-use mate- (epoxidized purifed vegetable oil—EPVO) and neat vegeta- rial (which can be collected from food outlets, households ble oil (epoxidized neat vegetable oil—ENVO) according to etc.) is aligned with sustainable principles [33–35]. Since previous reported methodologies [33]. Super Sap CLR® Part WVO becomes a non-edible feedstock after the frying pro- A was used as the epoxy part A (DGEBA, Entropy Resins, cess, its use alleviates potential pressures on the commodity United States) and a part B of hardener (mixture of iso- food price caused by the exploration of vegetable oils in phorone diamine and 1,3-benzenedimethanamine, Entropy engineering applications [36, 37]. Additionally, its valorisa- Resins, United States) as the benchmark epoxy. tion combats hazardous practices of human and animal con- sumption of reprocessed oil [38]. Finally, the use of WVO Flax Fibre Modifcation as a technological feedstock also diminishes environmental impacts associated with the production phase of the resin For the mercerization treatment, fax fbres (40 × 40 cm 2 as WVO can be assumed as a burden-free feedstock [39]. plies) were immersed in aqueous NaOH solution (4 wt%) at The incorporation of WVO-derived triglycerides into room temperature and remained under stirring for 1 h. The epoxy-based polymer networks has been recently demon- 4 wt% concentration was chosen as it has previously been strated in the literature [33]. Partially bio-based matrices shown to produce fbres with the highest tensile strength enabled the production of composites with recycled carbon [41]. After this time, fbres were carefully washed with dis- fbres by resin casting with maximum of Young’s Modulus tilled water to remove excess NaOH and oven dried (Ther- of 3.2 GPa and a tensile strength of 53 MPa. This investi- moScientifc Heraterm, 95 °C for 6 h). Fibres obtained gation permitted further development of networks entirely from this methodology were denominated NFF. For the derived from epoxy resins synthesised from WVO [40]. In treatment with stearic acid, fax fbres (40 × 40 cm2 plies) the current study, we report the frst production of a library were submerged in a 3 wt% stearic acid solution in ethanol of composites exploring the combination between WVO- and continuously stirred at 70 °C for 1 h. 3 wt% treatment based matrices with fbres such as glass and fax. These with stearic acid has previously been used to improve the matrices are compared to analogues produced from neat mechanical properties of natural fbres [42]. After the treat- vegetable oil to investigate efects of the use-phase in the ment, fbres were oven dried (ThermoScientifc Heraterm, resulting networks. The study also investigates the use of 95 °C for 6 h). Fibres obtained through this methodology diferent molar ratios of curing agent in the system, aiming are denominated SFF. to fnd the best balance between fnal properties of the ther- moset and renewable content. Chemical modifcation steps Composite Manufacturing were implemented to NFRC in order to improve fbre/matrix adhesion and produce more competitive materials from a Reinforcing fbres were cut into 40 × 40 cm 2 squares from mechanical performance standpoint. the roll of material, and oven dried (ThermoScientifc Her- aterm) at 95 °C for 4 h prior to the lamination. In order to obtain panels of suitable thicknesses for the mechanical Materials and Methods tests (2 mm), two plies of fax fbres and four plies of glass fbres were used in the lamination process. After drying, Materials fbres were weighed to allow the calculation of the resin content required to produce formulations with constant vol- Waste vegetable oil (used for deep frying for 4 days, a ume fraction (30 vol%) of the reinforcing agent. This strat- blend of rapeseed/palm oil approximately 3:1) and pre-use egy was adopted to manufacture panels presenting similar 1 3 Journal of Polymers and the Environment level of reinforcement agents despite the inherent diferences nomenclature, with NFF and SFF sufx indicating the