Volume 11 Issue 4

The key point of design for timber-concrete composite structure is to ensure the reliability of shear connectors. This study examined the mechanical properties of bolt-type connectors in timber-concrete composite structures theoretically and experimentally. The theoretical study was based on the Johansen yield theory (European Yield Model). Push-out specimens with different bolt dimensions were tested to determine the shear capacity and slip modulus. According to the experimental results, bolts yielded without timber or concrete cracks when the stiffness of bolts was not very great. The shear capacity and slip modulus of the bolt connectors were directly proportional to the diameter of the bolt. The strength of concrete was found to significantly affect the shear capacity of bolt connectors. Comparison between the theoretical and the experimental shear strength results showed reasonable agreement.

The aim of this paper is to present the opinions of professionals from the pulp and paper industry about employee development, as well as the necessity of competent employee retention. These opinions are different as a result of different expectations of employees and managers. The methodology of the paper is based on the following axiom: managers prioritize the processes of human resources management closely related to key employee retention improvement. To achieve the aim of the study, the largest pulp and paper companies in Slovakia were selected. Human resource managers and other professionals were asked about their opinions and attitudes about developing and retaining employees. Results of the research established that pulp and paper companies in Slovakia are significantly reflecting changes in technology and organization of work in the process of employee development. These companies also adopt the values and impacts of an intercultural environment in human resource management systems. The most important process affecting the development of employees is the possibility of professional training and development of competencies improving the performance. Due to changes in the external and internal environment, it is necessary to periodically review and assess the effectiveness of the policies and procedures affecting the development and retention of the employees.

Wood extractives, especially polyphenols, have great influence on the xylem colour of many wood species, which affects the success of hydrothermal wood processing, such as wood drying. One such wood species is European black alder (Alnus glutinosa (L.) Gaertn.), which is prone to forming intense and uneven reddish-orange or reddish-brown discolourations immediately upon harvesting and processing. However, there is lack of published scientific data on the wood and bark extractives of black alder, as well as the most suitable solvents to extract them. In this work, total soluble extractives, phenols, and flavonoids have been quantified in the wood and bark of black alder. Furthermore, the influence of four different polar organic solvents and deionized water on extractives removal yields has been measured. It was found that the bark has much higher levels of extractives as compared to the wood. Furthermore, it has been found that the highest extractive yields were obtained by using methanol as the extraction solvent for all observed compound group classifications.

In this study, straw was degraded continuously for 150 days under one of three levels of relative air humidity (RH) (90%, 60%, or 30%) to estimate the effect of humidity on straw biodegradation. Moreover, straw was treated with ultraviolet (UV)-A irradiation + 90% RH for 180 days to evaluate the interaction between photodegradation and biodegradation. The effects of 30% and 60% RH on straw degradation was inconspicuous. Straw mass losses at 90% RH and UV-A + 90% RH were 18.5% and 39.1%, respectively. BIOLOG analysis showed that filamentous fungi played a major role in straw biodegradation. Thermogravimetric analysis showed that treatment with UV-A + 90% RH tended to increase the maximum pyrolysis rate and decreased the initial pyrolysis temperature. Compared with 90% RH, infrared spectra analysis showed that functional groups of UV-A + 90% RH treatment, e.g., –CH, –C=O, and the benzene ring structure, clearly decreased. Straw-degrading bacteria were observed by scanning electron microscopy at the beginning and end of UV-A + 90% RH treatment. Results highlight the role of humidity in the degree of straw biodegradation by filamentous fungi. Straw degradation is accelerated by the combined action of photodegradation and biodegradation under high UV-A irradiation and high humidity.

In this study, reducing the density of oriented strand board (OSB) in the core layer where strands were replaced by rape straw particles was evaluated. The use of rape particles in the core layer did not significantly affect the mechanical properties of OSB. This type of board had only slightly deteriorated properties compared with conventional OSB. However, with a decreasing density, significant changes occurred in the modulus of rupture (MOR) and modulus of elasticity (MOE) determined for the shorter axis. The lowest possible density value was determined based on statistical analysis, allowing for the production of OSB that met the requirements of EN 300 (2006) for OSB type 3. The analysis showed that panels of this type can be produced at a density of 530 kg/m3.

Bacterial cellulose is a common research additive in the paper industry because it has unique and favorable characteristics. In this study, the effect of adding bacterial cellulose to an alkyl ketene dimer (AKD) sizing agent was investigated to optimize the dosage of bacterial cellulose, the retention system (cationic starch (CS), cationic polyacrylamide (CPAM)), and the sizing enhancement agents (polyamideamine-epichlorohydrin (PAE) and chitosan). The results showed that the addition of bacterial cellulose had a negative effect on AKD sizing. Meanwhile, the addition of 5% bacterial fiber had a slight but negligible effect on paper sizing. The retention system improved AKD sizing and the dual retention system with CS, and CPAM improved sizing up to 60%. When 0.2% PAE and chitosan were added simultaneously, the sizing degree increased by 42.8% and 47.6%, respectively.

Three dispersion instruments (a standard laboratory disintegrator, PFI beater, and ultrasonic cell disrupter) were tested to determine their effects on the dispersion of bacterial cellulose (BC) wet films. After treatment with a standard 10000 r disintegrator treatment, there was still a large number of undispersed fiber bundles in the BC suspension. The BC films were dispersed well after PFI beating revolution at 30000 r, and the cationic charge demand of the BC suspension reached 2.4 × 10-4 eq·g-1. The ultrasonic cell crusher was altogether unsuitable for BC dispersion. The ultrasonic cell crusher only separated the BC from the bundles. The properties of the resulting paper indicated that the physical strength of paper containing BC dispersed by the PFI beater was higher than that of the sample produced via standard laboratory disintegrator. Well-dispersed BC was distributed evenly among the plant fibers, which benefitted the combination of BC and plant fiber to improve the physical properties of the paper sheets.

The effect of spiral grain angle on the cutting power was tested during plane milling of Scots pine wood. It is known that cutting resistance depends on the arrangement of grain in relation to the direction of woodworking operations. In this work, up-milling (conventional cutting) was applied, as well as two woodworking techniques: with the grain and against the grain. Tests were conducted on samples differing in their position at the stem cross-section, one located closer to the circumference with the spiral grain angle of 11.5° and the other located closer to the pith, in which the spiral grain angle was 7.5°. This analysis confirmed significant differences in cutting power recorded for different values of spiral grain angle and depending on the applied cutting techniques. Cutting power at milling with the grain was greater than at milling against the grain. For samples with a smaller spiral grain angle a lower cutting power was recorded than for samples with a greater spiral grain angle. Differences in cutting power requirement between milling with the grain and against the grain increase with an increase in spiral grain angle.