Search

The pursuit for sustainability in the papermaking industry calls for the elimination or reduction of synthetic additives and the exploration of renewable and biodegradable alternatives. Cellulose nanofibrils (CNFs), due to their inherent morphological and biochemical properties, are an excellent alternative to synthetic additives. These properties enable CNFs to improve the mechanical, functional, and barrier properties of different types of paper. The nanosize diameter, micrometre length, semicrystalline structure, high strength, and modulus of CNFs have a direct influence on the mechanical properties of paper, such as tensile index, burst index, Scott index, breaking length, tear index, Z-strength, E-modulus, strain at break, and tensile stiffness. This review details the role played by CNFs as an additive to improve strength properties of paper and the factors affecting the improvement in paper quality when CNFs are added as additives. The paper also includes techno-economic aspects of the process and identifies areas that need further research.

This study optimizes a novel surfactant-assisted green liquor dregs (GLD) pretreatment of paper mill sludge (PMS), both of which are wastes from the kraft pulping industry, using a combined Response Surface Methodology (RSM) design. Optimized conditions give a maximal reducing sugar release of 16.38 g/L. A substantial reduction in heavy metals aluminum, chromium, cobalt, arsenic, lead, and copper after pretreatment illustrates the enhancement of substrate digestibility by reducing toxic elements. Separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF) for hydrogen production are assessed. SSF produced a hydrogen yield of 3.72 mL/g, displaying a 36.26% increase from pretreated PMS compared to SHF. These findings provide insights into possible methods of reducing process duration, energy input, and costs incurred with waste disposal within the paper industry. Furthermore, improved hydrogen yield using an SSF process demonstrates the potential beneficiation of pulp and paper GLD and PMS wastes.

The accumulation of petrochemical plastic waste is detrimental to the environment. Polyhydroxyalkanoates (PHAs) are bacterial-derived polymers utilized for the production of bioplastics. PHA-plastics exhibit mechanical and thermal properties similar to conventional plastics. However, high production cost and obtaining high PHA yield and productivity impedes the widespread use of bioplastics. This study demonstrates the concept of cyclic fed-batch fermentation (CFBF) for enhanced PHA productivity by Bacillus thuringiensis using a glucose-rich hydrolyzate as the sole carbon source. The statistically optimized fermentation conditions used to obtain high cell density biomass (OD600 of 2.4175) were: 8.77 g L−1 yeast extract; 66.63% hydrolyzate (v/v); a fermentation pH of 7.18; and an incubation time of 27.22 h. The CFBF comprised three cycles of 29 h, 52 h, and 65 h, respectively. After the third cyclic event, cell biomass of 20.99 g L−1, PHA concentration of 14.28 g L−1, PHA yield of 68.03%, and PHA productivity of 0.219 g L−1 h−1 was achieved. This cyclic strategy yielded an almost threefold increase in biomass concentration and a fourfold increase in PHA concentration compared with batch fermentation. FTIR spectra of the extracted PHAs display prominent peaks at the wavelengths unique to PHAs. A copolymer was elucidated after the first cyclic event, whereas, after cycles CFBF 2–4, a terpolymer was noted. The PHAs obtained after CFBF cycle 3 have a slightly higher thermal stability compared with commercial PHB. The cyclic events decreased the melting temperature and degree of crystallinity of the PHAs. The approach used in this study demonstrates the possibility of coupling fermentation strategies with hydrolyzate derived from lignocellulosic waste as an alternative feedstock to obtain high cell density biomass and enhanced PHA productivity.

The South African pulp and paper industry generates an estimated 0.5 million tons of pulp and paper mill sludge (PPMS) annually. As PPMS is generated, it requires safe, efficient, and economical co...

An organic–inorganic functionalized nano-filler (CNC–TiO2), was prepared by loading titanium dioxide nanoparticles (TiO2) onto the crystalline nanocellulose (CNC) surface by using methacrylatesilane as cross-link agent in order to enhance compatibility between nanofiller and matrix (PMMA). Nanocomposite films (PMMA/CNC–TiO2) were prepared by free radical copolymerization of various amount (0–5 wt%) of functionalized nanofiller (CNC–TiO2) with methylmethacrylate (MMA) as main monomer, followed by solvent casting technique. The films were characterized using TEM, FTIR, FEG-SEM, and XRD, TGA, and UV–VIS spectroscopy. The results of TEM and FTIR confirmed the modification of CNC with TiO2 and the interaction between the CNC–TiO2 nanofiller and PMMA. FEG-SEM results showed a uniform dispersion of the nanofiller in the PMMA matrix whereas EDX confirmed the presence of TiO2 in the nanocomposite films. The effect of the nanofiller on the mechanical properties of PMMA was also investigated and the results showed significant improvement in tensile and modulus strengths with increasing amounts of nanofiller. In addition, TGA results demonstrated remarkable improvements in the thermal properties of the PMMA/CNC–TiO2 nanocomposite films UV results showed a response to UV absorbance due to incorporation of TiO2. Nanocomposite films can be beneficial for a variety of applications such as coating materials for windows, shelters, glazing, optical filters, and as hard packaging with UV-blocking properties.

New biobased polycaprolactone (PCL) nanocomposite materials were prepared using cellulose-zinc oxide (NCC-ZnO) as an organic–inorganic nanofiller which was prepared by loading zinc oxide (ZnO) onto the surface of nanocrystalline cellulose (NCC). Various loadings (2–8 wt%) of nanofiller were added onto the PCL matrix to prepare PCL/NCC-ZnO nanocomposite films using the solvent cast method. The nanofiller and nanocomposite films were characterised by AFM, TEM, FTIR, FE-SEM, XRD, DSC, TGA and tensile strength. The results of AFM, TEM and FTIR analysis confirmed the interaction between NCC and ZnO nanoparticles and between nanofiller (NCC-ZnO) and PCL. The mechanical properties of the PCL polymer significantly improved due to incorporation of the nanofiller, especially, when increasing the amount of nanofiller beyond 4 wt%. FE-SEM analysis showed homogenous dispersion of nanofiller within the PCL matrix, and illustrated a rough porous surface. Both TGA and DSC results indicated that the thermal stability of PCL increased due to the incorporation of nanofillers.

The beneficiation of sludge from pulp and paper mills to produce high-value products such as crystalline nanocellulose will alleviate the challenges associated with conventional methods of sludge disposal, such as landfilling and incineration. In addition, the use of sludge will reduce the consumption of fresh raw materials in the synthesis of nanocellulose which is usually produced from high-purity cellulose pulps. In this study, fibres were cleaned and separated from sludge and then converted to crystalline nanocellulose using ammonium persulphate under optimised oxidative conditions. To extend potential applications of the crystalline nanocellulose produced, the crystalline nanocellulose was functionalised with zinc oxide, silver and hydroxyapatite to prepare crystalline nanocellulose-zinc oxide, crystalline nanocellulose-silver and crystalline nanocellulose-hydroxyapatite nano- and micro-composites powders using the sol–gel process. Transmission electron microscopy, field-emission scanning electron microscopy, X-ray diffraction and thermo-gravimetric analysis were used to investigate the properties of crystalline nanocellulose and functionalised crystalline nanocellulose. The transmission electron microscope and field-emission scanning electron microscope coupled with energy-dispersive X-ray spectroscopy confirmed the synthesis of crystalline nanocellulose, and inorganic nanoparticles. Functionalised samples (crystalline nanocellulose-zinc oxide, crystalline nanocellulose-silver and crystalline nanocellulose-hydroxyapatite) showed better thermal stability than pure crystalline nanocellulose. This implies that the modified inorganic crystalline nanocellulose composites could be used in applications where thermal stability is desirable. The cost of production is economically viable as the raw material cost is cheaper compared to the use of wood pulp.

A quantitative method has been developed for assessment of the distribution of xylan across the secondary cell wall layers of Eucalyptus dissolving pulp fibres by means of a carbohydrate binding module (CBM), CtCBM6, in combination with transmission electron microscopy (TEM). To ensure reproducibility and to minimise non-specific labelling, various parameters were optimised, namely the size of the gold colloid marker, CtCBM6 concentration, and the selection of buffer solutions. The method was replicated on processed Eucalyptus fibres containing different xylan contents. Reproducible xylan counts and distributions across the secondary cell wall layers were obtained for unbleached and bleached Eucalyptus fibres. The xylan distribution pattern across the cell wall layers S1, S2 and S3 was similar, but the S1 and S3 layers contained after bleaching more xylan than the S2 layer. The technique has a wide range of applications in basic wood research as well as in the analysis of technological processes.

Pulp and paper mill sludge is a waste stream derived from the pulp and paper making industry, comprised of organic and inorganic material in the form of cellulose, hemicellulose, lignin and ash. In South Africa, approximately fivefour hundred thousand wet tonnes are produced per annum and is currently disposed via landfilling or incineration. However, these disposal methods raise environmental and financial concerns. This waste stream is an attractive feedstock for fermentable sugars, mainly glucose, recovery and can be redirected for valorisation as a feedstock for microbial fermentation to produce value-added products. Sugar recovery by enzymatic hydrolysis, as opposed to acidic hydrolysis, is a promising approach but is hampered by the lignin and inorganic material found in pulp and paper mill sludge. Several treatment steps to reduce or remove these components prior to enzymatic hydrolysis are assessed in this review. Pretreatment improves hydrolysis of cellulosic fibres and ensures a substantial yield of sugars.

The original version of the article unfortunately contained an error in Author names and the affililiations.

Bleached hardwood and softwood South African kraft pulps were passed through a commercially available micro grinder for varying number of passes and the properties of the resultant pulps were assessed periodically using microscopy, Fourier transform infrared spectroscopy (FTIR), X-ray crystallography (XRD) and Thermogravimetric analysis (TGA). The ultrastructural analysis of the pulp fibres revealed that after 120 passes both hardwood and softwood bleached fibres showed the presence of cellulose nanofibres (CNFs). The FTIR analysis showed no modification to the cellulose structure and side groups upon treatment with the supermasscolloider (SMC). Both hardwood and softwood pulp fibres showed a decline in crystallinity after SMC treatment. For the hardwood pulps there were no major differences between the untreated pulps and those passed through the SMC. In the case of the softwood pulps, the SMC treatment resulted in more thermally stable CNFs compared with the untreated bleached pulps. This was observed at several levels of treatment (40, 120 and 200 passes). After 200 passes both the hardwood and softwood kraft pulp fibres produced CNFs with an average width of 11 nm and lengths with several micrometers.