Ionic liquid mediated technology for fabrication of cellulose film using gutta percha as an additive

Highlights

• Cellulose/gutta percha hybrid films were fabricated by ionic liquid technology.

• Gutta percha was obtained from E. ulmoides Oliver after a multiple-step process.

• The crystalline structure of transparent films was altered from cellulose I to II.

• The smooth films showed excellent strength, thermal stability and oxygen barrier.

• The properties of films were modulated by altering the weight of gutta percha.

Abstract

A great paradigm for state-of-the-art biomaterials is to use renewable lignocelluloses with ionic liquid-based green regimes. Novel transparent films were successfully prepared from the purified eucalyptus cellulose by the moderate incorporation of gutta percha (GP, 5–15%) using 1-butyl-3-methylimidazolium acetate ([bmim]OAc) as a versatile solvent. The refined GP was obtained from Eucommia ulmoides Oliver after hot-water extraction, alkaline treatment, enzymatic hydrolysis, and extended petroleum ether purification. The cellulose/GP films exhibited a well-distributed and smooth structure, and the crystalline structure of composite films was transformed from cellulose I to II. The incorporation of 5–10% GP obviously improved the tensile strength of films (129–139 MPa) as compared to the pure cellulose film (81 MPa). Moreover, the novel hybrid films showed excellent thermal stability and oxygen barrier property as a result of the reinforcement by GP. The cellulose/GP films with prominent tensile strength, thermal stability and oxygen permeability could be tuned via varying the ratio of GP to cellulose matrix, which can be exploited as a potential candidate of pollution-free, biodegradable and renewable cellulose-based composites for the substitute of petroleum derived packaging materials.

Introduction

The recent upsurge of research interest has been dedicated on the development of biodegraded and green biomaterials from lignocellulosic biomass as a potential alternative of fossil-derived materials to reduce environmental pollution resulted from non-biodegradable plastic films (Cao et al., 2010, Fernandes et al., 2009). Crystalline polysaccharides of biomass are auspicious for noteworthy and rapidly growing applications ranging from advanced energy storage, electronics, and catalyst or enzyme supports to tissue engineering and biological devices (Huang et al., 2017). Among them, cellulose is the most abundant polysaccharide in lignocelluloses, which possesses unparalleled physicochemical properties such as biodegradability and biocompatibility and has a large number of current and potential applications (Siró and Plackett, 2010). There is no doubt that cellulose-based materials have attracted vast research interests in the fields of fibers, films, food casings, and membranes (Qi et al., 2009, Turner et al., 2004). However, cellulose has often suffered from solubility problems due to the presence of hydrogen bonds, hindering the improvement of their processability, fusibility, and functionality (Pinkert et al., 2009). To date, only a limited number of cellulose solvent systems have been found, for example, LiCl/N,N-dimethylacetamide (DMAc), N-methylmorpholine-N-oxide (NMMO) (Zhang et al., 2005). As the best one of amine-oxides, NMMO system is the solely industrialized solvent for the manufacture of regenerated cellulose fibers and films. However, these solvents have some limitations such as volatility, toxicity, unsafety, difficult recovery, and instability in application (Zhang et al., 2005). Ionic liquids (ILs), the low-melting point salts that are liquids at temperature below 100 °C, have recently found to be used as excellent solvents for cellulose (Wang et al., 2012, Zhang et al., 2014). As the novel and multifaceted media, ILs have a series of superior properties, such as admirable thermal stability, negligible vapor pressure, and tunable properties with respect to hydrophobicity, polarity, and solvent miscibility through appropriate combination of anions and cations (Brandt et al., 2013, Petkovic et al., 2011). Thanks to these unique properties of ILs, the IL-mediated technology has been considered as an efficient method to produce novel cellulosic hybrid composites. ILs with acetate anions have been expounded to exhibit excellent solvating power, low melting points and viscosities, low toxicity and corrosivity, and high hydrogen bonding acceptor abilities (Sun et al., 2009). An impressive recyclability of 1-butyl-3-methylimidazolium acetate ([bmim]OAc) was also affirmed (Xu et al., 2017). Representatively, films have been facilely prepared by the regeneration of the biopolymers from solutions in acetate ILs (Abdulkhani et al., 2013, Soheilmoghaddam et al., 2014).

In general, the packaging composites are potentially subjected to a variety of external forces that require a certain mechanical properties to resist the outside pressure and scratch. However, cellulose-based materials often suffered from their frangible feature and inferior mechanical strength that impede the exploitation of bio-based composites in a wide range of applications (Orelma et al., 2011). Various types of additives, such as plasticizer and polymers, could be affiliated to cellulose for improving the mechanical strength and specific properties of the regenerated cellulose membrane. Gutta percha (GP), also called balata or Eucommia-rubber, is a thermoplastic crystalline polymer with a molecular structure of trans-1,4-polyisoprene from Eucommia ulmoides Oliver and an isomer of natural rubber (Sun et al., 2013, Zhang et al., 2008). GP is a hard, fibrous and long-chain natural rubber resource that exhibits properties similar to plastic and is suitable for various industrial uses (Sun et al., 2013; Zhang et al., 2011). In addition, GP can be extracted from the whole of certain tissues or organs (such as seed coats 12–18%, barks 6–12% and leaves 1–3%) of Eucommia ulmoides Oliver tree and is resistant or agglomerate to acids and alkalis, which is used extensively in electrical insulation and filling material. Trans-1,4-polyisoprene is easy to crystallize due to its regular macromolecular chain structure. Two crystalline forms, α-form and the β-form, can be obtained by crystallizing at room temperature from the molten state which directly affects macroscopic mechanical behavior (Zhang et al., 2011). Because of the trans-configuration and high degree of polymerization of GP, it has distinct properties and functions with the duality of flexibility and plasticity. With these properties, GP can blend with natural polymers to obtain mixtures exhibiting special functions which do not present in individual rubbers, plastic, and polymers (Takeno et al., 2008, Zhang and Xue, 2011, Zhang et al., 2008). Therefore, GP is a potential additive to improve the unique features, such as mechanical strength and fabricability, with a wide range of applications in the fields of polymer, pharmaceutical, and thin film materials.

Herein, for the first time, the use of ([bmim]OAc) as the solvent was explored to fabricate the hybrid cellulose films in the presence of GP for improving the hydrophobicity tensile strength, thermal stability, and barrier properties of cellulose-based films and thus facilitating their actual commercialization. The physicochemical structure, thermal stability, mechanical properties, and oxygen permeability of the hybrid films with the different cellulose/GP weight ratios were investigated to aid a holistic understanding of the interplay between the structure and performance of hybrid cellulose films and evaluate the feasibility of their applications in the fields of packaging and functional materials. This study offers an effective and facile method to produce cellulose-based biocomposites with excellence performances for green and value-added utilization of woody biomass.