Elsevier

Industrial Crops and Products

Volume 168, 15 September 2021, 113607
Industrial Crops and Products

Tannin-furanic foams modified by soybean protein isolate (SPI) and industrial lignin substituting formaldehyde addition

https://doi.org/10.1016/j.indcrop.2021.113607Get rights and content

Highlights

  • Series of tannin-furanic-SPI foams with excellent fire performance were prepared.

  • The SPI improved strength and diminished pulverization ratio markedly of foams.

  • Lignin greatly upgraded the flame retardancy of tannin-furanic-SPI foams.

  • New reactions of tannin and SPI formed strong covalent networks was described.

Abstract

Soybean protein isolate (SPI) was tested in this study as a crosslinker and formaldehyde substitute for preparing high biomass content sustainable rigid tannin-furanic-SPI (TFS) and lignin-tannin-furanic-SPI (LTFS) versatile foams. Additionally, flame retardancy was improved by lignin used as a natural fire-retardant. Fourier-transform infrared spectroscopy (FT-IR), coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF-MS), revealed a covalent cross-linking reaction between tannin and SPI. TFS and LTFS foams showed by scanning electron microscopy (SEM) a closed cell structure without any pores. The incorporation of SPI resulted in enhanced mechanical properties and reduced pulverization ratios, improved thermal stability and increased thermal conductivity (approximately 0.042–0.044 W/m K compared with control foam. Furthermore, the TFS foams exhibited outstanding flame retardancy and suppressed smoke generation while undergoing combustion. These results were supported by a higher limiting oxygen index (LOI) value, a lower heat-release rate, and a higher char residue, obtained by LOI and cone calorimetry. The addition of lignin further enhanced the thermal properties and flame retardancy of TFS foams although it decreased their mechanical performance. The TFS and LTFS foams were environmentally friendly, as shown by the low formaldehyde emission measurements. This novel sustainable TFS foam appears to have a good potential for industrial application.

Introduction

Sought-after characteristics, such as flame retardancy, better thermal stability, lightweight, and thermal insulation, are found in phenolic foam (PF). Yet PF has high friability and inferior mechanical properties and is a fossil fuel-based resource, which limits somewhat its large-scale commercial applications (Chen et al., 2020a; Wu et al., 2020). Therefore, foams with improved mechanical properties using natural renewable feedstocks have attracted much attention. Condensed tannin—a vegetal polyphenolic material which is widespread—has been applied in several field (Chen et al., 2020a; Meikleham and Pizzi, 1994; Pizzi, 2019).

Phenolic tannin-furanic-formaldehyde foams were first reported by Meikleham and Pizzi in 1994 and have since received significant attention (Meikleham and Pizzi, 1994; Pizzi, 2019). The interest of these foams is not only because they are based on a renewable resource but also because of theirs self-blowing preparation under ambient/moderate temperature, and their comparable performance with commercial PF foams (Meikleham and Pizzi, 1994; Pizzi, 2019; Tondi and Pizzi, 2009; Tondi et al., 2008a, c; Zhou et al., 2019).

The preparation approaches for these foams are based on a heat-generated expansion initiated by a blowing agent evaporation coupled with an acid-catalysis self-condensation of furfuryl alcohol, without (Basso et al., 2011) or with a cross-linker ensuring the foam structure does not collapse (Celzard et al., 2010; Tondi et al., 2009b; Tondi and Pizzi, 2009; Tondi et al., 2008a, c; Zhou et al., 2019). Various foams have been obtained for different application fields, such as rigid, semi-rigid, and flexible foams via formulation and/or processing adjustment (Basso et al., 2014a, b; Basso et al., 2011; Celzard et al., 2011, 2010; Lacoste et al., 2013; Li et al., 2012c; Meikleham and Pizzi, 1994; Pizzi, 2019; Tondi et al., 2009a, b; Tondi and Pizzi, 2009; Tondi et al., 2008a, c; Zhou et al., 2019). Yet, because of their brittleness they powder easily on frictioning them and present lower mechanical compression properties, these foams have limited commercial application. Their susceptibility to powdering under friction has been solved well (Rangel et al., 2016). However, to reduce the foam brittleness and to enhance other properties (flame retardancy, thermal stability, and thermal insulation) so as to achieve their industrialization, some improved formulations have been developed by introducing organic/inorganic additives, such as polymeric diphenylmethane diisocyanate (p-MDI) (Li et al., 2012a), hyperbranched poly(amino-ester) (Li et al., 2012b), multi-walled carbon nanotubes (Li et al., 2013), disordered carbon matrix and graphite fillers (Jana et al., 2015), cellulose nanofibers (CNF) (Zhou et al., 2019), wood cellulosic fiber(Wu et al., 2020), hydroxy-methylated lignin (Pizzi, 2019) and boric and/or phosphoric acid (Celzard et al., 2011). Formaldehyde-free modifications have been introduced early on to take into account human health and the environment. Thus, formulations with no aldehydes at all (Basso et al., 2013, 2011), or with non-toxic and non-volatile aldehydes such as glyoxal and glutaraldehyde (Lacoste et al., 2013), or fossil-based resources such as PEG-400 and polymeric diphenylmethane diisocyanate (p-MDI) (Li et al., 2012a), and biorefinery byproduct such as polyfuranic humins (Chen et al., 2020a) have been reported as the part of feedstocks that can replace formaldehyde to produce tannin-furanic foams. Mechanical or/and chemical expansion methods have also been utilized to prepare tannin-based rigid foams with lower density, thermal insulation, and robust cell structure (Santiago-Medina et al., 2018a, b; Szczurek et al., 2014).

Plant or animal proteins have also attracted attention for their successful utilization for bio-foams preparation. Albumin was initially used to design and manufacture flexible biofoams (Basso and Pizzi, 2017; Basso et al., 2015; Li et al., 2012c, d) with a series of different natural albumin and albumin/tannin cellular foams following (Basso and Pizzi, 2017; Basso et al., 2015; Lacoste et al., 2015). Biomass foams based on wheat gluten have also been reported (Chiou et al., 2020). However, soy flour and soy protein isolate (SPI) are plant-sourced, renewable, sustainable, and easily obtained from soybean-oil production processing, which is why it has been a commonly applied bioresource for the food industry (Guo et al., 2018; Ma et al., 2020), film preparation (Cao et al., 2007; Gu et al., 2019; Wang et al., 2017), in biomedicine (Zhao et al., 2018), and for wood adhesive applications (Liu et al., 2017; Zhao et al., 2018). SPI was once the main raw material or reinforcement filler for different kinds of foam design (Frihart and Lorenz, 2019; Frihart et al., 2019; Liu et al., 2017, 2015; Wang et al., 2019; Xi et al., 2020; Xiao et al., 2013; Zhao et al., 2019). This encouraged us to design and investigate SPI for tannin-furanic foam preparation because of the reputed reaction crosslinking reaction between tannin and SPI (Ghahri et al., 2018a; Ghahri and Pizzi, 2018; Ghahri et al., 2018b; Liu et al., 2017) as only a small amount of SPI addition can achieve unexpected effectiveness.

Thus, here are presented novel mimosa tannin-furanic-SPI (TFS) and lignin-tannin-furanic-SPI (LTFS) versatile foams. Lignin was selected as the natural flame-retardant to improve the flame retardancy of the-resultant TFS foams. The reaction between tannin and SPI was examined. The combined properties of the control, TFS, and LTFS foams, including apparent density, morphology, pulverization ratios, and mechanical properties, were systematically evaluated. Furthermore, the thermal stability, thermal conductivity, and especially fire retardancy of the foams were investigated. The formaldehyde emission of the foams obtained was determined to further demonstrate its environment-friendly characteristics.

Section snippets

Materials

Commercial mimosa tannin extract (Acacia mearnsii, De Wild, its main components as shown in Table S1) was provided by Silva Chimica (St. Michele Mondovi, Italy). Soy protein isolate (SPI) was purchased from Ruikang Biotechnology Co., LTD (Dezhou, China). Lignin was obtained from Anhui BASF Biotechnology Co. LTD (Anhui, China). Furfuryl alcohol (FA, 98 %), Formaldehyde (F, 37 %), p-toluene-4-sulfonic acid (p-TSA, 65 %) and Diethyl ether (DE, 98 %) were purchased from Sigma-Aldrich (Saint Louis,

The preparation of tannin-furanic-SPI foams

The fabrication of versatile tannin-furanic-SPI foams with high biomass content (∼88 %) derived from natural lignocellulosic biomass-derived products (furfuryl alcohol and tannin) and a sustainable soybean derivative (SPI) is schematically illustrated in Fig. 1. This formulation avoided the toxic formaldehyde utilization, improving the fabrication safety and environmentally friendly nature of the foams with enhanced properties.

There are a number of simultaneous reactions occurring, as described

Conclusions

High biomass, environment-friendly, and flame retardant TFS foams were developed in this study. Mechanical properties, thermal performance, and flame retardancy were measured by substituting SPI for formaldehyde.

The main results obtained were:

  • (1)

    A strong crosslinking reaction between tannin and SPI, yielding closed cells foam structures, thus enhancing mechanical properties, reducing pulverization ratios, and improving thermal conductivity (approximately 0.042–0.044 W/m K of the modified tannin

CRediT authorship contribution statement

Xinyi Chen: Conceptualization, Methodology, Software, Data curation, Writing - original draft. Jinxing Li: Methodology, Software, Investigation, Writing - original draft. Antonio Pizzi: Conceptualization, Data curation, Writing - original draft. Emmanuel Fredon: Visualization, Supervision. Christine Gerardin: Supervision. Xiaojian Zhou: Conceptualization, Data curation, Writing - review & editing, Funding acquisition. Guanben Du: Supervision, Writing - review & editing, Funding acquisition.

Declaration of Competing Interest

The authors declare no conflict of interest.

Acknowledgement

This work was supported by National Natural Science Foundation of China (NSFC 31760187, 31971595), Yunnan Provincial Natural Science Foundation (2017FB060), the “Ten-thousand Program”-youth talent support program and Yunnan Provincial Reserve Talents for Middle & Young Academic and Technical Leaders (2019HB026), Scholarship from China Scholarship Council (CSC), Yunnan Provincial Key Laboratory of Wood Adhesives and Glued Products. The LERMAB is supported by a grant of the French Agence

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    These authors contributed equally to this work.

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