polymers Article Effect of Lemon Waste Natural Dye and Essential Oil Loaded into Laminar Nanoclays on Thermomechanical and Color Properties of Polyester Based Bionanocomposites Bàrbara Micó-Vicent 1,4 , Valentin Viqueira 1 , Marina Ramos 2 , Francesca Luzi 3 , Franco Dominici 3 , Luigi Torre 3 , Alfonso Jiménez 2 , Debora Puglia 3, * and María Carmen Garrigós 2, * 1 Colour and Vision Group, University of Alicante, San Vicente del Raspeig, ES-03690 Alicante, Spain; barbara.mico@ua.es (B.M.-V.);valentin.viqueira@ua.es (V.V.) 2 Department of Analytical Chemistry, Nutrition & Food Sciences, University of Alicante, San Vicente del Raspeig, ES-03690 Alicante, Spain; marina.ramos@ua.es (M.R.); alfjimenez@ua.es (A.J.) 3 Department of Civil and Environmental Engineering, University of Perugia, 05100 Terni, Italy; francesca.luzi@unipg.it (F.L.); francodominici1@gmail.com (F.D.); luigi.torre@unipg.it (L.T.) 4 Department of Appl. Stat. & Operat. Research, & Qual., Universitat Politècnica de València, ES-03801 Valencia, Spain; barbara.mico@gmail.com * Correspondence: debora.puglia@unipg.it (D.P.); mc.garrigos@ua.es (M.C.G.) Received: 11 June 2020; Accepted: 25 June 2020; Published: 28 June 2020   Abstract: In this work, polyester-based nanocomposites added with laminar nanoclays (calcined hydrotalcite, HT, and montmorillonite, MMT) loaded with lemon waste natural dye (LD) and essential oil (LEO) were prepared and characterized. The optimal conditions to synthetize the hybrid materials were obtained by using statistically designed experiments. The maximum LD adsorption with HT was found using 5 wt% of surfactant (sodium dodecyl sulfate), 5 wt% of mordant (aluminum potassium sulfate dodecahydrate) and 50% (v/v) ethanol. For MMT, 10 wt% of surfactant (cetylpyridinium bromide), 5 wt% of mordant, 1 wt% of (3-aminopropyl) triethoxysilane and 100% distilled water were used. LEO adsorption at 300 wt% was maximized with MMT, 10 wt% of surfactant and 50 ◦ C following an evaporation/adsorption process. The obtained hybrid nanofillers were incorporated in a polyester-based matrix (INZEA) at different loadings (3, 5, and 7 wt%) and the obtained samples were characterized in terms of thermal stability, tensile behavior, and color properties. HT_LEM-based samples showed a bright yellow color compared to MMT_LEM ones. The presence of lemon hybrid pigments in INZEA-based systems produced a remarkable variation in CIELAB color space values, which was more visible with increasing the nanofillers ratio. A limited mechanical enhancement and reduced thermal stability was observed with the nanopigments addition, suggesting a limited extent of intercalation/exfoliation of MMT and HT in the polymer matrix. MMT_LEM pigments showed higher thermal stability than HT_LEM ones. A significant increase in Young’s modulus of nanocomposites loaded with hybrid LEO was observed compared to the biopolymer matrix. The LEO inclusion into the nanoclays efficiently improved its thermal stability, especially for MMT. Keywords: lemon waste; natural pigments; essential oils; experimental design; nanoclays; bionanocomposites 1. Introduction Ecological concerns related to the use of synthetic dyes have motivated industries to consider the replacement of these compounds by eco-friendly non-toxic natural dyes to minimize the negative Polymers 2020, 12, 1451; doi:10.3390/polym12071451 www.mdpi.com/journal/polymers