Volume 36, Issue 3

Within-tree variation of four handsheet properties (burst index, sheet density, STFI short-span compression strength (STFI) and tensile index) was mapped for loblolly pine trees aged 13 and 22 years using NIR predicted handsheet property data (representing an average of 18 trees for each age). All within-tree maps were similar demonstrating a radial decrease in handsheet properties at all heights, with sheet density and tensile index having the greatest within-tree variation. The corewood zone had the highest values for all properties, while the lowest values were observed in a region consistent with juvenile and transitional outerwood as defined by Burdon et al. (2004). The maps are also similar to, but the inverse of, maps reported in prior studies for density and tracheid coarseness and wall thickness. Relationships amongst the examined handsheet properties and wood and tracheid properties explains the overall similarities of the different maps. The maps provide a representation of within-tree variation of important paper properties at two different ages. An understanding of how these properties vary within loblolly pine trees can aid in better utilization of forest resources.

Kraft pulping kinetic models are an important component of any fundamental continuity based continuous digester model. These models can be used to further develop our understanding, or as a framework to support the development of real-world control, estimation and optimization strategies. Effective models are tailored to a specific species of wood and must be applicable for a wide range of expected cooking conditions. In this work a series of experiments were conducted on hardwood Aspen chips for 5 different cooking conditions. Each series of cooks were interrupted at different time intervals to capture the dynamic response of the cook. The key chips and liquor components were measured and reconciled at each interval. A dynamic model was then developed based on a simplification of a continuous digester model under batch conditions. This ensures continuity between the key assumptions governing both the batch kinetics model and the expanded continuous form. A kinetic model structure was adapted from the literature that quantifies all three accepted phases of lignin and cellulose degradation, i. e. the initial, bulk and residual phases as well as the effect of modern cooking practices such as intra-cook white liquor addition on the transition between the bulk and residual phases. Additionally, modifications were made to the kinetic model structure to reduce the overall number of states and to impose a floor limit on degradation, thereby reducing the overall complexity and computational burden. The model was then fit to the data using weighted least squares and simulation optimization techniques.

More than 70 % bleached chemical pulp is produced in India through elemental chlorine-free bleaching in which chlorine-based compounds like chlorine dioxide is a dominant chemical which generates chlorinated organic toxins harmful to the environment. Present studies demonstrate short sequence of bleaching combined with acid treatment, followed by pressurized oxygen delignification. It was found that efficiency of oxygen improved by adding hydrogen peroxide as an additive in oxygen delignification with subsequent treatment with ozone or chlorine dioxide as bleaching agents. It was observed that by using additive in ODL process, pulp can achieve 70±1 (%ISO) brightness. Reduction attains in kappa number 65–70 % as compared to 45–50 % in control oxygen delignification stage. Through AOpZ and AOpD bleaching sequences, full brightness achieved 84–85 (%ISO) without considerable loss in mechanical strength properties compared to DEpD sequence. A potential reduction in COD, color, and AOX was 28, 53.3, and 88 % respectively were observed in AOpZ short bleaching sequence compared to DEpD bleaching.

Production of mechanical pulps requires high specific electrical energy compared to many other attrition processes. In Scandinavia, the lowest specific refining energy for production of thermomechanical pulp is around 1800 kWh/t for newsprint quality, which is roughly 60 times higher than for crushing of stone to a similar size distribution. The high specific energy demand for refining has naturally motivated large efforts in the search for improved efficiency. It is always practical to be able to quantify improvements in efficiency for comparison of process designs and of different machine types. However, there is no commonly accepted definition of efficiency for mechanical pulping processes. In published work within mechanical pulping, energy efficiency has been presented in different ways. In this paper, we discuss definitions of energy efficiency and aspects that ought to be considered when energy efficiency is presented. Although focus of this work is on energy efficiency for refiner processes, the principles can be applied to other types of mechanical pulping processes such as stone groundwood.

The ash condensation ability of the cigarette paper is an important factor affecting the cigarette grades. In this study, we put forward an effective method of improving this ability. Xanthan gum was successfully synthesized, applied as an ash integrator in the dip-coating process of cigarette paper production, and showed good performance. Cationic guar gum, cellulose phosphate and Hydroxyapatite (HAP) have been added in the pulp and showed better performance of the ash condensation property. The ash become much whiter and the scatter of the ash have been suppressed. Moreover, the further addition of HAP would result in a worse combustion efficiency, leading to the burning out of the cigarette in early time.

The in-situ synthesis of calcium silicate in the fiber can not only meet the requirements for high loading of paper, but also make up and improve the reduction of paper performance caused by filling. In this investigation, the effects of pulp type, beating degree, fiber ratio, reaction time, rotational speed, dosage of lime milk and dispersant on calcium silicate loading and paper properties were investigated. The results showed that when the beating degree was 40 °SR, the ratio of softwood and hardwood pulp was 1:1, the reaction time was 60 min, the rotation speed was 600 r·min −1 , the dosage of lime milk was 1.33 times of the theoretical amount, and the dosage of cationic polyacrylamide was 0.3 % (absolutely dry pulp), the ash content of hand-made sheet was 41.2 %, and the loading amount of calcium silicate was 26.3 %. Under this condition, the comprehensive performance of paper was the best.

The objective in this work was to obtain a fine fraction of kraft pulp, with as high concentration as possible, in a pilot-scale fractionation with micro-perforated screen baskets. The influence of screen basket surface, hole size, feed concentration, pulp type and refining segment design was investigated. The results showed that a smooth screen basket surface improved the fractionation efficiency of the unrefined pulp compared to a profiled screen basket, despite a larger hole size. A significantly higher fine fraction concentration was obtained when using refined hardwood pulp compared to when using softwood pulp, which was explained with its lower average fibre length and narrower and thus more flexible fibre fragments. The pilot trials also showed that the screening process could be operated at feed concentrations similar to those directly after a refiner, 30–40 g/l. This was demonstrated in a process layout with partial recirculation where a refiner and a micro-perforated screen basket were operated in series in pilot scale.

Mixed hardwood unbleached (UB) and final bleached (FB) pulp along with the pulp of intermediate bleaching stages from an integrated paper mill have been undertaken for this study. Headspace GC-MS analysis of these pulps was made to identify the odorous compounds which are volatile organic compounds (VOCs), generated during ageing for 60 days. The result showed that a number of pre-generated VOCs such as aliphatic hydrocarbons and aldehydes are observed in the pulp sample which might be came from the process and it has been observed that upon ageing at ambient conditions, some acid functionalized VOC were generated in the pulp. The generation of these VOCs were established by ATR-FTIR analysis and the results showed that intensity of peak absorbance near 3340  cm − 1 {\text{cm}^{-1}} and 1641  cm − 1 {\text{cm}^{-1}} which represents the –OH stretching of acidic functional group and C=O stretch of aldehyde and acidic functional groups increased after ageing. Generation of acid functionalized volatile compounds were observed more in bleached pulp than in unbleached pulp. Degree of polymerization (DP) is pretty much related to the strength of paper. DP of both unbleached and bleached pulp gets reduced upon ageing while more reduction were observed in bleached pulp. Bleached pulps are more prone to degrade as compared to the unbleached pulp in terms of strength properties such as tensile index, breaking length, burst and double fold were observed. 12.3 % and 21.8 % reduction in tensile index was observed for UB and final bleached FB pulp respectively. Burst index of UB and FB pulp were found reduced to 23.8 % and 41.9 % respectively due to ageing. Reduction in the mechanical and optical properties was also observed in intermediate bleaching stages. There is much evidence for the contribution of VOCs to the degradation of paper. The results are strongly suggested that acid functionalized volatile compounds can have strong effects on degradation of cellulosic paper.

Bagasse sugarcane (BSC) has low fibre strength due to low cellulose content. Hence, by adding a strong secondary fibre that is high in cellulose such as pineapple leaf fibre (PALF), the fibre strength of the system can be improved. High portion of PALF decreased the composite paper performance because the high composition of PALF tends to produce flocs and agglomerates fibres. The arrangement of the fibres in composite paper should be improved so that this agglomerate’s effect could be overcome. A novel multilayer hybrid fibre composite was used. BSC/PALF with several hybrid ratios was studied in terms of the mechanical and moisture properties of the produced paper sheet and the results showed that multilayer hybrid composite paper produced higher in hybrid composite paper’s properties compared with random hybrid composite paper. The colour of multilayer hybrid fibre composite paper resembled the natural bright colour of BSC and the multilayer hybrid fibre composite paper also shown a slightly low weight loss percentage compared with the random hybrid fibre composite paper after 60 days of soil burial test. As a conclusion, multilayer hybrid fibre composite produced the stronger interfibre bonding and overcome the agglomerate’s effect between BSC/PALF compared with random hybrid fibre composite.

Large deformations under in-plane compression of paperboard appear in forming processes like hydroforming, pressforming and deep drawing, but the mechanisms of deformation have not been studied on a micromechanical level. A constrained in-plane compression test is presented. This test allows for in-plane compression, buckling, wrinkling and compaction. The constrained compression test is realized using a DEBEN CT-500 in-situ tester for laboratory microtomography and synchrotron microtomography. Experiments with five different materials spanning from laboratory handsheets to commercially available multi-layered paperboards are performed. Image processing is used to observe the local out-of-plane fiber orientation and compaction. A phenomenological investigation of the deformation behavior of these materials is presented. Delamination is found to be the primary mechanisms of failure in the multi-layered boards. Furthermore, a porous network structure, created by using long and minimally refined softwood fibers, is found to facilitate the formation of uniform wrinkles and compaction.

A series of tung oil-rosin-based polyester (TRP) used as internal sizing agents were prepared using rosin, tung oil, maleic anhydride, and glycerol. TRP structure and properties were examined using Fourier transform infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The TRP latexes were subsequently used as internal sizing agents, and the sizing properties were evaluated using a scanning electron microscope (SEM), a video-based dynamic contact angle measuring device and a Cobb absorbency tester. The optimal conditions for preparing the TRP sizing agent were as follows: the hydroxy-carboxyl ratio of the material was 0.25; the maleic anhydride dosage was 20 % of rosin; and the tung oil dosage was 40 % of rosin. Under the best conditions, the sized paper Cobb-60 was 15.6  g / m 2 \text{g}/{\text{m}^{2}}, the tensile index was 45.1 N·m/g, the burst index was 3.1 kPa· m 2 {\text{m}^{2}}/g, and the tear index was 15.6 mN· m 2 {\text{m}^{2}}/g.

Improving the utilization rate of fly ash (FA) and realizing its resource utilization has always been a popular research topic in the application field of solid waste recycling. This paper aims to improve the basic brightness of fly ash (FA) before calcium carbonate coating, and realize the filling application of fly ash in medium and high-end paper. Taking advantage of the high brightness of molecular sieves (MS) (brightness ≥ 90 %ISO), the alkali melting hydrothermal synthesis (AM-HS) method was used to generate high brightness MS on the surface of fly ash. The results showed that the optimum conditions of alkali melting hydrothermal synthesis (AM-HS) modification were as follows: the mass ratio of sodium hydroxide to fly ash was 1:1, the time of hydrothermal modification was 6 h, the temperature of hydrothermal modification was 80 °C, and the brightness reached to 64.54 %ISO; The results of SEM, particle size analysis and ultrasonic vibration showed that the surface of fly ash is covered by MS and has strong binding effect.

Cellulose based nanomaterials have the great potential to be applied to paper as bulk additive or coating material to improve overall final properties, especially in secondary fiber. In the present work, the effect of applying different kinds of cellulose nanofibrils (CNF) to papers obtained from recycled fibers using size press on physical, mechanical and barrier properties was investigated and compared with the sole use of starch as coating material. The coating process of CNF was carried out by the addition of size press grade starch to coating suspension. As a cellulose source, wheat straw was evaluated and CNF was obtained through oxidative and enzymatic pretreatments. Results indicate that starch/CNF suspension improves the overall paper properties. As a result of the deposition of coating suspension contains of 4 % wt. periodate-oxidized CNF onto paper surface, tensile and burst indices of papersheets increased as 52.2 % and 194.4 %. Significant decreases were observed in air permeability as 69.8 %. Compression tests also have been conducted to evaluate papersheets end-use properties. In comparison to the other pretreated CNF, due to is lower viscosity, applying periodate-oxidized CNF as size press significantly increased the mechanical properties of the papers fabricated from the recycled pulps.

Precipitated calcium carbonate (PCC) filler is used in many industrial products like constructions, plastics, pharmaceutics, etc. In this study producing cationic precipitated calcium carbonate filler for paper industry was investigated. Hence, a cationic polyacrylamide and cationic corn starch have been incorporated into the PCC particles to produce a modified filler with cationic structure and improved hydrogen bonding ability with cellulose fibers. According to the FESEM and XRD results, cubic-like fillers with prominently calcite polymorph and a slight amount of aragonite were successfully produced from the industrial burnt lime using carbonation process. The presence of organic substances in the structure of the modified samples was confirmed by FT-IR analysis. Besides, based on the FESEM results, filler morphology and particle size could be affected by the polymer content. In conclusion, introducing cationic groups to mineral fillers could be considered as a possible strategy to overcome some detrimental effects of using mineral fillers in paper products.