polymers Article Effect of Almond Shell Waste on Physicochemical Properties of Polyester-Based Biocomposites Marina Ramos 1 , Franco Dominici 2 , Francesca Luzi 2 , Alfonso Jiménez 1 , Maria Carmen Garrigós 1, * , Luigi Torre 2 and Debora Puglia 2, * 1 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.) 2 Department of Civil and Environmental Engineering, University of Perugia, 05100 Terni, Italy; francodominici1@gmail.com (F.D.); francesca.luzi@unipg.it (F.L.); luigi.torre@unipg.it (L.T.) * Correspondence: mc.garrigos@ua.es (M.C.G); debora.puglia@unipg.it (D.P.) Received: 15 March 2020; Accepted: 1 April 2020; Published: 6 April 2020   Abstract: Polyester-based biocomposites containing INZEA F2 ® biopolymer and almond shell powder (ASP) at 10 and 25 wt % contents with and without two different compatibilizers, maleinized linseed oil and Joncryl ADR 4400 ® , were prepared by melt blending in an extruder, followed by injection molding. The effect of fine (125–250 m) and coarse (500–1000 m) milling sizes of ASP was also evaluated. An improvement in elastic modulus was observed with the addition of< both fine and coarse ASP at 25 wt %. The addition of maleinized linseed oil and Joncryl ADR 4400 produced some compatibilizing effect at low filler contents while biocomposites with a higher amount of ASP still presented some gaps at the interface by field emission scanning electron microscopy. Some decrease in thermal stability was shown which was related to the relatively low thermal stability and disintegration of the lignocellulosic filler. The added modifiers provided some enhanced thermal resistance to the final biocomposites. Thermal analysis by differential scanning calorimetry and thermogravimetric analysis suggested the presence of two different polyesters in the polymer matrix, with one of them showing full disintegration after 28 and 90 days for biocomposites containing 25 and 10 wt %, respectively, under composting conditions. The developed biocomposites have been shown to be potential polyester-based matrices for use as compostable materials at high filler contents. Keywords: almond shell waste; reinforcing; polyester-based biocomposites; physicochemical properties; disintegration 1. Introduction Almond is characterized by its high nutritional value, although information reported so far mainly concerns its edible kernel or meat. Other parts also present in the almond fruit are the middle shell, outer green shell cover or almond hull and a thin leathery layer known as brown skin of meat or seed coat [1]. Almonds are used as a fruit in snack foods and as ingredients in a variety of processed foods, especially in bakery and confectionery products. However, almond production generates large amounts of almond by-products since the nutritional and commercial relevance of almonds is restricted to the kernel. In particular, almond shell is the name given to the ligneous material forming the thick endocarp or husk of the almond (Prunus amygdalus L.) tree fruit. It is principally composed of cellulose (ranging from 29.8 to 50.7 wt %), hemicellulose (from 19.3 to 29.0 wt %) and lignin (from 20.4 to 50.7 wt %) [1]. This by-product is normally incinerated or dumped without control, which results in the production of large amounts of waste and pollution [2]. Several researchers have focused on different alternatives for using almond shell wastes based on their potential uses as biomass to produce renewable energy [3]; as a source of organic biopesticides [4], heavy metal Polymers 2020, 12, 835; doi:10.3390/polym12040835 www.mdpi.com/journal/polymers