Characterization of three non-product materials from a bleached eucalyptus kraft pulp mill, in view of valorising them as a source of cellulose fibres

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Abstract

This paper is a contribution of scientific knowledge on the characteristics of several by-product materials from a bleached eucalyptus kraft pulp mill. In fact, three industrial wastes arising from bleached hardwood kraft pulps, namely: unbleached screen rejects (USR), effluent treatment (ETW), and eucalyptus bark (EB) were analyzed with the aim of their possible valorization as an alternative source of cellulose. Pure powder cellulose, CEAL, from Aldrich was also analyzed, as a reference. The structural, thermal, and morphological study of these raw materials were carried out by Fourier transform infrared spectroscopy (FTIR), energy dispersion spectrometry (EDS), X-ray diffraction (XRD), thermogravimetry (TG), temperature modulated differential scanning calorimetry (TMDSC) and scanning electron microscopy (SEM). Their morphological properties were determined using MorFi apparatus. For this study the sample bleached kraft pulp, BKP, was analyzed as a reference. Lignin and carbohydrate contents were also quantified. These by-products were studied as such (i.e. without careful purification) because we intended to find rational and low-cost way of valorization. In fact any additional operation will induce an over cost. The results obtained indicate that these industrial wastes can be potential raw material in fibre-based applications (paper, composites, …), since they contain a high proportion of cellulose with preserved fibrillar morphology and good thermal stability. Some of these materials have low lignin and inorganic residue contents.

Introduction

The paper consumption is constantly increasing and new application based on the use of cellulose fibres has also gained a growing interest last decades. This trend becomes much more pronounced if one considers the search for using renewable material in order to reduce the growing environmental threat and to slow down the rate of depletion of petrochemical resources (Satyanarayana et al., 1971, Wollerdorfer and Bader, 1998, Gandini and Belgacem, 2002). Thus, one possible strategy in the attempt of using natural fibres in composite materials is their tensile stress (up to 1500 MPa) and elastic modulus (from 40 to 130 GPa) (Gindl et al., 2006). These performances make cellulose fibres potential candidate to substitute other homologues (for instance glass counterparts), since the recycling of the formers by energy recovery is much easier to handle to compare with the latter-based composites. In fact, there is no solid residue to treat at the end of combustion in the case of cellulose-based materials. Moreover, being renewable, vegetal fibres may be used as an alternative material due to their biodegradability, low specific mass, low cost, and availability.

Among the vegetal fibres, cellulose is the most abundant natural polymer. Detailed studies are found in literature describing its chemical structure (Klemm et al., 1998), thermal stability (Soares et al., 1995, Soares et al., 2001), and surface modification (Gandini and Belgacem, 2005). Several applications of cellulose, either as a fibrous or a micro-granular material, show that this natural fibrous material may become one of the main renewable sources for the near future. Thus, cellulose bead, for example, may be used in controlled drug delivery (Morales et al., 2004, Wolf, 1997), production of derivatives of industrial interest such as viscose (Stepanik et al., 2000), biomass fuel production (Spatari et al., 2005), electrical transformer thermal insulation (Emsley, 1994), catalysis and chromatography gels (Grznárová et al., 2005), civil engineering (Savastano et al., 2000), car industry (Pervaiz and Sain, 2003), and polymer-based composites (Simon et al., 1998, Bledzki and Gassan, 1999, Redondo et al., 2003, Silva and Silva, 2005, Bullions et al., 2006).

In the present work, samples of industrial process materials were kindly supplied by Celulose Nipo-Brasileira S.A. (CENIBRA), a producer of bleached cellulose pulp from Eucalyptus grandis by kraft process were characterized by chemical composition and structure, thermal behavior, and morphology, in order to propose potential applications. The CENIBRA mill is located in Belo Horizonte and the plantation of Eucalyptus grandis is near to the geo-coordinates of 19°19′S, 42°23′W.

Section snippets

Characterization and methods

The wastes studied here are noted according to their origin in the cellulose pulp production process, namely: eucalyptus bark (EB), unbleached screen rejects (USR), which corresponds to unbleached screen reject, and effluent treatment waste (ETW). It is worth to mention that the debarking process was a dry one and the raw material studied was outer bark (5–7 years old). This should avoid the extraction of any substances from the bark waste. The ETW fraction corresponds to the sludge from the

Chemical characterization of fibres

The lignin and carbohydrate contents were determined, as summarized in Table 1, which shows that all the three industrial wastes are quite rich in cellulose and hemicelluloses content, even if the composition of EB is close to that of wood. The chemical composition of the other two wastes (USR and ETW) is carbohydrate-rich pure raw material. Thus, the content of polysaccharides in USR and ETW is 92.4 and 84.5%, respectively. In a first approximation, glucose content can be attributed to

Conclusions

The structural characterization of industrial residues showed that they possess interesting features, which makes them potential candidates to be used as raw fibrous material. Thus, the residues studied showed that they: (i) high quantities of polysaccharides, (ii) their thermal resistance were close to that of reference cellulose fibres, (iii) their Cp values were lower than that obtained for model cellulose samples, as they are they contain amorphous substances (lignin) and inorganic fillers

Acknowledgments

The authors thank CENIBRA for samples and Capes and CNPq for financial support.

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