Comparative effects of organic and inorganic bio-fillers on the hydrophobicity of polylactic acid Abraham K. Aworinde a, * , Samson O. Adeosun a, b , Festus A. Oyawale a , Esther T. Akinlabi a, c , Stephen A. Akinlabi a, c a Mechanical Engineering Department, College of Engineering, Covenant University, Ota, Ogun State, Nigeria b Metallurgical and Materials Engineering Department, University of Lagos, Nigeria c Mechanical Engineering Science Department, University of Johannesburg, South Africa ARTICLE INFO Keywords: Melt-blending Organic Bio-filler Methyl Group Hydrophobicity of PLA ABSTRACT The use of Polylactic acid (PLA) has been limited in the biomedical field because of its slow degradation profile which is traceable to its degree of hydrophobicity. In this work, 16.67 wt. % of chitosan (Ch), chitin (Ct) and titanium (Ti-6Al-2Sn-2Mo-2Cr-0.25Si) (Ti) powders weremelt blended with PLA and the resulting composites examined using Fourier Transform Infrared Spectroscopy (FTIR). Chitosan was found to reduce the hydrophobic peak due to δ s (CH 3 ) in PLA by 13.92%, chitin by 10.65% and titanium by 8.04%. Summarily, the organic bio- fillers produced more hydrophilic PLA composites than the inorganic filler. The percentage reduction in hydro- phobicity renders the developed composites more suitable for orthopaedic applications. 1. Introduction Polylactic acid (PLA) is a thermoplastic polymer belonging to the α-hydroxy acid family [1–3]. It has become a choice material due to its amazing characteristics. However, its high level of hydrophobicity has rendered it clinically unsuitable for use in the biomedical field [4] because of the difficulty in the formation of apatite (a bone-bonding material) [5] and slow degradation profile [14]. The degree of hydro- phobicity found in PLA has been traced to the presence of large methyl groups, CH 3 , which are non-polar, covalent groups [2,6]. Attempts have been made by researchers to develop a more biodegradable PLA com- posites [7–10] but none has stated in a quantitative term the percentage reduction in its hydrophobic contents. To successfully influence the behavioural characteristics of a hydrophobic polymer via composite production with a hydrophilic filler, critical factors such as volume fraction, filler pre-treatment, compositing method, etc. are remarkable [11]. This work studied and stated quantitatively the effect of organic fillers (chitosan and chitin) and inorganic additive (titanium powders) on the reduction rate of CH 3 , the essential radical that is responsible for hydrophobicity in PLA. 2. Materials and method Polylactic acid (PLA) pellets with a molecular weight of 144 g/mol were purchased from Natureworks, China. 16.67 wt. % of chitosan, chitin and titanium (Ti-6Al-2Sn-2Mo-2Cr-0.25Si) powders were each melt- blended, in turn, with PLA at 290  C and mould-pressed to form solid cylinders (Ø ¼ 12.5 mm, l ¼ 7 mm). The solids were crushed into powder- like and subjected to Fourier Transform Infrared Spectroscopy exami- nations. Spectra were recorded at 32 scans with a resolution of 2 cm 1 . The transmittance measurements were carried out in the range 400–4000 cm 1 . MATLAB R2019a was used to filter the noisy regions and superimpose the spectra for comparison. 3. Results and discussion Fig. 1 shows the Fourier Transform Infrared Spectroscopy (FTIR) re- sults while Table 1 lists the characteristic infrared bands found in PLA and its composites. The examinations of the peaks showed that there were neither removal of peaks nor formation of new peaks. This is similar to the observations of other researchers [12,13]. This implies that the compositing method employed achieved more of a physical mixture process between the matrix and the fillers used than a chemical reaction. It also shows that the three bio-fillers did not significantly affect the molecular structure of PLA. The sharp peaks at 1748 and 1183 cm 1 are indicative of the carbonyl group. A carbonyl group is essentially a func- tional group composed of a carbon atom double-bonded to an oxygen atom. It is a group with strong electron-withdrawing tendency with * Corresponding author. E-mail address: abraham.aworinde@covenantuniversity.edu.ng (A.K. Aworinde). Contents lists available at ScienceDirect Results in Engineering journal homepage: www.editorialmanager.com/rineng/Default.aspx https://doi.org/10.1016/j.rineng.2020.100098 Received 3 October 2019; Received in revised form 21 January 2020; Accepted 21 January 2020 2590-1230/© 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by- nc-nd/4.0/). Results in Engineering 5 (2020) 100098