polymers Article The Use of Laminates of Commercially Available Fabrics for Anti-Stab Body-Armor Nguyen Quang Khuyen 1 , Phan Vu Duc Han 2 , Ngoc Tuan Nguyen 2 , Quoc Bao Le 1 , Madis Harjo 3 , Gholamreza Anbarjafari 4 , Rudolf Kiefer 1, * and Tarmo Tamm 3   Citation: Khuyen, N.Q.;Han, P.V.D.; Nguyen, N.T.; Le, Q.B.; Harjo, M.; Anbarjafari, G.; Kiefer, R.; Tamm, T. The Use of Laminates of Commercially Available Fabrics for Anti-Stab Body-Armor. Polymers 2021, 13, 1077. https://doi.org/10.3390/ polym13071077 Academic Editor: Francisco Javier Espinach Orús Received: 26 February 2021 Accepted: 26 March 2021 Published: 29 March 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Conducting Polymers in Composites and Applications Research Group, Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam; nguyenquangkhuyen@tdtu.edu.vn (N.Q.K.); lequocbao@tdtu.edu.vn (Q.B.L.) 2 Faculty of Applied Sciences, Ton Duc Thang University, Ho Chi Minh City 700000, Vietnam; phamvuduchan1@gmail.com (P.V.D.H.); nguyenngoctuan@tdtu.edu.vn (N.T.N.) 3 Intelligent Materials and Systems Lab, Institute of Technology, University of Tartu, Nooruse 1, 50411 Tartu, Estonia; madis.harjo@gmail.com (M.H.); tarmo.tamm@ut.ee (T.T.) 4 iCV Research Lab, Institute of Technology, University of Tartu, 51009 Tartu, Estonia; shb@ut.ee * Correspondence: rudolf.kiefer@tdtu.edu.vn; Tel.: +886-905605515 Abstract: Modern personal protective armor has been generally based on the Kevlar fabrics, with the main goal to offer defense against bullets. In addition to the high cost and poor processability, Kevlar has the disadvantage of limited stab-proofing capability. On the other hand, a large number of crimes involving deadly injures represent knife attacks. Our goal in this work was to investigate composites based on traditional commercially available fabrics of linen and silk, using different adhesives- polymers for forming laminates. The silk composites also contained different amounts of in-woven polyester. Three different water-based adhesives of polyurethane, urea formaldehyde and polyvinyl alcohol were considered. It was found, that besides the strength of the fabrics themselves, the adhesives polymers played a crucial role in the obtained performance of the laminates. The laminates were characterized in their mechanical properties, as well as with scanning electron microscopy and FTIR spectroscopy. Keywords: linen; soft and hard silk; laminates; adhesives; shore hardness 1. Introduction Protective body-armor has a long history, as protection against arrows, spears and knives in battles was used in ancient times [1]. The application of linen laminates dates back 3000 years ago to the Egyptian empire, where lightweight, wearable and easy formable body-armor was used [1]. Contemporary studies [2] of linen laminates fabricated using ancient techniques and materials like linen seed adhesives have found that a certain protection against knives and arrows could indeed be obtained through their use. In ancient Asian cultures, body-armor made from silk was used and further laminated with silver plates [1], making the armor easily wearable and lightweight. Today, protective body-armor for police and military forces is largely based on Kevlar fabrics [3], with the main goal to protect the wearer from bullets. In most cases, pure Kevlar fabrics do not possess stab- proof properties, but composites with linen have shown reasonable stab-proofing [4], with silica-coated Kevlar wool being another option showing good results [5]. Perhaps more so than bullet penetration, stab-penetration is a function of many parameters, including blade sharpness and geometry, cutting angle and velocity, etc. [6]. While knives of different characteristics and quality can lead to different performance, the general process from indentation/puncture to penetration is the same. Stab and punctuation resistance depends on the relative interaction strength of friction of the yarns (fabrics) and the knife, as well as inter-yarn frictions [7]. Addressing these aspects, attempts have been made to influence Polymers 2021, 13, 1077. https://doi.org/10.3390/polym13071077 https://www.mdpi.com/journal/polymers