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This study investigated the performance of recycled polypropylene (RPP)/peanut shell powder (PSP) composites with untreated PSP and treated PSP with alkaline peroxide. The RPP/PSP and RPP/PSP-H2O2 composites were prepared by melt mixing and compression molding at different PSP loadings (10 wt.% to 40 wt.%). The samples were characterized by processing properties, tensile properties, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and water absorption behavior. The treated PSP enhanced the stabilization torque, tensile strength, elongation at break, tensile modulus, and water absorption of RPP/PSP-H2O2 composites. FTIR spectra and SEM showed that the elimination of lignin content strongly influenced the fractured surface and chemical characteristics of the RPP/PSP-H2O2 composites.

Primary refined coarse softwood thermomechanical pulp was treated with alkaline peroxide prior to low-consistency (LC) refining. The effects of the pre-treatments on pulp quality, refinability, and electrical energy consumption were assessed. Four pre-treatments were conducted with alkali charges of 2.5 and 6% and peroxide charges of 3 and 4%. The pulps were refined to specific energies up to 600 kWh/t by multiple passes through an LC refiner at intensities of 90 and 150 kWh/t. It was found that alkaline peroxide treatments increased tear strength and protected the fibre from cutting, especially during high intensity refining below a specific energy of 300 kWh/t. Treatment with 6% NaOH and 4% or 3% H2O2 led to lower brightness gains and scattering coefficients but increased the tensile strength index by 31%, potentially lowering the total electrical energy required to achieve strong pulp. The enhancement of tensile strength caused by the highly alkaline peroxide mostly resulted from increased bonding, which was attributable to acid group generation rather than the promotion of further fibrillation during LC refining.

Four fiber fractions from poplar alkaline peroxide mechanical pulping, performed with refiner-chemical preconditioning (P-RC APMP), were used to estimate inter-fiber bonding capacity. The relationship between fiber characteristics and inter-fiber bonding capacities was investigated. The surface lignin content of the long fiber fraction was slightly lower than that of the short fiber fraction. Atomic force microscopy (AFM) images showed that the fiber surfaces were heterogeneous (i.e., different cell wall layers were exposed along the fiber surface). The fiber fractions that had lower surface lignin content had higher bonding capacities. Furthermore, modified PFI beating was used to peel the surface of the fibers. After the peeling treatment, the fiber surface charge increased remarkably, while the surface lignin concentration decreased considerably. The lignin and charge on the fiber surface are the two key factors for estimating the inter-fiber bonding capacities.

To reduce the refining energy consumption of chemi-mechanical pulping, treatment with NaOH-thiourea-urea aqueous solution was studied in this work. By means of single-factor experiments, the effects of alkali dosage, soaking time, and freezing time were evaluated. It was found that the optimal conditions were an alkali dosage of 8%, soaking time of 45 min, and freezing time of 105 min. The results revealed that refining energy consumption could be reduced by approximately 40% under optimal conditions compared with that of alkaline peroxide mechanical pulp, while other pulping or paper-making properties were similar. There were no significant effects on the structure of the functional groups, the crystalline region of the pulp, or the whole structure of the treated wood chips. However, damage to single wood fibers on the chips treated in NaOH-thiourea-urea aqueous solution was more obvious.

In recent years, the alkaline peroxide mechanical pulping performed with refiner-chemical preconditioning (P-RC APMP) has obtained a wide application in many paper grades in China. This is due to such desirable pulp characteristics as its high bulk, opacity, and light scattering coefficient. However, compared with its bleached chemical pulps, the poplar P-RC APMP has weak bonding strength, which limits its application in value-added products. Usually, the interfiber bonding abilities of different fiber fractions are quite different. In this study, the page bonding strength index (B) and the interfiber bonding abilities (shear bond strength per unit area (b) and relative bonding area (RBA)) of different P-RC APMP fiber fractions were extrapolated by the traditional Page Equation. The results show that the higher B could be obtained when the fiber fraction was shorter or smaller. The same trend was observed for b and RBA. Wet pressing was used to improve the bonding ability, and higher pressure of wet pressing or shorter fiber fraction can lead to obviously higher tensile strength.

The chemical compositions of cotton stalk and bast are similar to those of hardwood and superior to those of grass fiber. With respect to the morphological characteristics of their fibers, cotton stalk is similar to hardwood and cotton bast is similar to softwood. The average length of cotton bast fibers is nearly triple that of cotton stalk fibers, and the length-to-width ratio is almost quadruple. Traditionally, cotton stalk and cotton bast are pulped together, which affects the quality and homogeneity of the pulp and complicates bleaching, limiting its use to low-grade paper. In this study, cotton bast and cotton stalk were separated and pulped individually by alkaline peroxide extrusion pulping (APEP). The orthogonal analytical method was used to determine the optimal pulping parameters. Compared to those obtained via the kraft pulp (KP) of cotton stalk as a whole, far superior yield and whiteness were obtained in APEP. Further, with APEP, lower amounts of chemicals and less energy were consumed and there was little pollution. The physical performance of APEP was slightly lower than that of KP. With respect to bast alone, the physical performance of APEP was almost as good as that of KP.

In the mechanical pulping process, some process state and product quality variables are difficult to measure on-line. In this paper, soft sensors were used to estimate Canadian Standard Freeness (CSF) and outlet consistency (Cout) after the high consistency refining stage of the alkaline peroxide mechanical pulping (APMP) process. After the secondary variables for modeling that are readily available processed measurements in pre-treatment and the HC refining stage was selected, models based on the case-based reasoning (CBR) method were developed to estimate CSF and Cout. The ability of CBR soft sensors to predict CSF and Cout was tested using data collected from an APMP mill, and the results were satisfactory. Additionally, two typical soft sensor methods that back propagation network (BP) algorithms and support vector regression algorithms (SVR) were employed to predict CSF and Cout and evaluate the performance of the CBR soft sensor. As a result, the proposed soft sensor demonstrated a better performance than the BP method and can be regarded as of comparable quality to the SVR method.

In China, alkaline peroxide mechanical pulping performed with refiner-chemical preconditioning (P-RC APMP) is well known to produce fiber with high bulk, opacity, and light scattering coefficient but weak bonding and strength properties. In this study, the characteristics of different P-RC APMP fiber fractions were investigated, and their effects on bonding strength properties were determined. The results showed that there was only 5.8% R30 fiber fraction and 14.1% P100/R200 fiber fraction, and the specific surface area increased from R30 to P100/R200. The tensile index increased by 51.85% and the bonding index increased by 15.35%, when the fibers were changed from the R30 fraction to the P100/R200 fraction. The short fiber fraction (P100/R200 fraction) had smaller fiber length and coarseness but larger specific surface area and greater surface charge density than the long fiber fraction (R30 fraction). The fiber specific surface area and surface charge density made significant contributions to the bonding capacity, whereas fiber coarseness and length were negatively correlated with the tensile index.

The properties of P-RC APMP effluent, including relative density, Baume degree, viscosity, surface tension, specific heat capacity, boiling point rise (BPR), and elemental contents of the effluent, were studied. Results indicated that relative density, viscosity, Baume degree, and solids content all displayed a direct proportional correlation; however, there was an inverse linear relationship between Baume degree and temperature. Viscosity rose sharply when the solids content was more than 40%. Surface tension gradually decreased with the rise of solids content. However, when the solids content was over 35%, it increased with an increase in solids content. Specific heat capacity was closely related to the solids content, but it was reduced with an increase in solids content. BPR was proportional to effluent solids content, especially when the solids content exceeded 30% with an uptrend in BPR.

Carboxymethyl cellulose (CMC)-assisted refining was shown, by means of tests with a PFI mill, to have potential to save energy compared with conventional refining techniques. Previously it was thought that the energy-saving effect of CMC-assisted refining was caused by resultant lubrication that reduced friction. In this work, the refined fiber of eucalyptus alkaline peroxide mechanical pulp was analyzed. The mechanism of CMC-assisted refining is that the cell wall is fibrillated to peel and weaken cell wall strength. Then CMC permeates into the cell wall and swells it, and the fiber becomes more pliable. CMC-assisted refining is helpful in maintaining fiber length through resultant hydration to avoid more fiber cutting. In this work, fiber morphological changes in the course of PFI refining for different numbers of revolutions were shown in relation to CMC-assisted refining. The purpose of the research was to determine whether energy savings could be achieved by CMC-assisted refining and to study its influence on fiber morphological development. The study showed a linear relationship between fiber length and energy consumption, as well as an exponential relationship between fines and fiber length. These results are helpful for obtaining ideal fiber morphology in pulp and paper making, man-made board, natural nano-fibers and specialty fibers, and the food industry.