Evaluation of the mechanical properties of compacted paraffin powders. Effect of formulation K. Dunchych a, ⁎, C. Loisel b , A. Arhaliass a , O. Gonçalves a , J. Legrand a , M. Pouliquen c , S. Saint-Jalmes c a Université de Nantes, - GEPEA UMR CNRS 6144, CRTT, boulevard de l'Université, 44600 Saint-Nazaire cedex, France b ONIRIS, CS 82225, 44322 Nantes, France c Denis et Fils, RN149 Recouvrance, 44190 Gétigné, France abstract article info Article history: Received 1 June 2017 Received in revised form 12 September 2017 Accepted 9 October 2017 Available online 18 October 2017 The mechanical characteristics of a paraffin–vegetable oil material and the compressive behavior of the powder stemming from this material were used to estimate the resistance of the compressed samples. The compressive behavior of powders under the low pressure range (1–2 MPa) applied in the candle industry was investigated in order to predict the tensile strength of the compressed samples. Compressive behavior was evaluated under lab conditions similar to those practiced in the candle industry. Compressive behavior of the powders, which represents the resistance of the particles to rearrangement during the packing step, K p (30.98 ± 1.20 kPa of the mixture M1), was positively correlated to tensile strength of the compressed samples, σ t (175.46 ± 3.61 kPa of mixture M1). Tensile strength of the compacts was also related to the mechanical properties of the raw material: high tensile strength was linked to low ductility (γ MR ), high mechanical strength (R MR ) and high Young's modulus (E) of the material. Formulation—particularly the presence of a lubricant of mineral (0.52%) and vegetable (44.1%) origin in mixture M5—was found to strongly influence the mechanical properties of the compressed samples (σ t = 115.52 ± 2.42 kPa). © 2017 Published by Elsevier B.V. Keywords: Mechanical properties Powder compressibility Paraffin Sustainability 1. Introduction The paraffin wax obtained from refining oil finds a wide range of applications in industry, medicine, and food, and is the main material used in compression-based candle manufacture. However, despite being in widespread use, the behavior of paraffin as a powder in compression has never yet been studied. Furthermore, research into alternative renewable materials of vegetable origin is thriving as the candle market looks for more sustainable sources. Several patents [1–3] state that the combination of alternative materials with paraffin wax has to meet the physical characteristics required, including controlled melting points, high malleability, low fragility, and high chemical stability. Vegetable oils of different origins (e.g. palm oil, rapeseed oil and olive oil) are candidates for mixing with paraffin, and the use of vegetable oils derived from vegetable waste is also described in certain patents [4]. In order to incorporate alternative materials in the candle, one has to verify their compatibility with a com- plex mechanical process, i.e. compression, to guarantee the quality of the final candle product. The compression process is widely used in many industrial sectors, from pharmacy and metallurgy to cosmetics and foods. The success of the compression is related to the mechanical properties of the material [5–6] and of the powder bed, i.e. the ability of the powder to decrease in volume under pressure (compressibility) [7–11] and form a cohe- sive compact by densification (compactibility) [12–13], the transmis- sion of forces through the powder volume [14–15], the mechanism involved in the cohesion of the tablet (solid bridges, forces of attraction, entanglements) [16–17], and inter-particle/wall friction during the compression [18–20]. All these parameters play an important role in the formation of a cohesive compressed sample. The mechanical properties of the materials themselves, such as the ductile or brittle character of the material and its hardness/softness characterized by Young's modulus [21–26], also have to be taken into account. These parameters depend on the nature of the forces involved and the structure and purity of the material. The behavior of the powder in compression is critical in the for- mation of the compressed sample. During compression, with the in- crease of the pressure, the powder undergoes intensive densification and the powder particles move together to generate cohesive forces [17,19,27]. Many studies have focused on the relationship between relative density of the powder and compaction pressure, considered as defining the compressibility of a material, and several models have been developed and modified to characterize the compressibility of powders [7–11,28]. When compression starts, the particles rear- range themselves by sliding and rotating to form a denser stack, thus Powder Technology 324 (2018) 85–94 ⁎ Corresponding author. E-mail address: kateryna.dunchych@univ-nantes.fr (K. Dunchych). https://doi.org/10.1016/j.powtec.2017.10.029 0032-5910/© 2017 Published by Elsevier B.V. Contents lists available at ScienceDirect Powder Technology journal homepage: www.elsevier.com/locate/powtec