A Study of an Effect on Moisture from 3D Printer Filament Drying Processes

This study investigated characteristics of moisture desorption for polylactic acid (PLA) filaments. The filaments tend to absorb moisture from humid air, led to moisten filaments. The absorption of even small amounts of moisture by filaments during storage and/or 3D printing, degraded the quality of final parts, and therefore, caused manufacturing problems. In this work, the filaments were subjected to humid conditions to achieve various moisture concentrations (0.75, 1.3 and 1.87 wt.%). Warm air-drying processes are used to reduce the moisture for different times (1, 2, 3, 4, 5 and 6 hours) and temperature (40, 50 and 60 °C). It was founded that the moisture from the polylactic acid (PLA) filaments can be discovered the moisture by use 60 degree of temperature in 5 hours warm air-drying process.

Effect of -O- on Water Molecule Adsorption and Adsorption Mechanism of Lignite and Coke

The high moisture content of lignite restricts its extensive and efficient use. Furthermore, the reabsorption of lignite is also a factor that affects lignite spontaneous combustion. Therefore, it is of great importance to study the process and mechanism of water molecule desorption and adsorption on lignite and coke (25–950°C) to achieve the clean and efficient utilization of lignite and environmental protection. Proton nuclear magnetic resonance (1H-NMR), thermogravimetric analysis, and other techniques were used in this study to explore the water molecule absorption and desorption processes of lignite pyrolysis at different temperatures (25–950°C) and the special contributions of ether bonds to water molecule adsorption. A mechanism of lignite water molecule adsorption was proposed. The results showed that ether bonds played a special role in the water molecule adsorption by pyrolyzed lignite. The ether bond content was greater in the coal samples at 300 and 950°C, which changed the trend of lignite water molecule absorption and the distribution of water (T2) detected in the 1H-NMR experiments and delayed the escape of water molecules during moisture desorption. The total amount of adsorbed water decreased first and then increased in the coal samples as the pyrolysis temperature increased. However, the maximum adsorption interactions of each coal sample increased first and then decreased. This was the result of the interactions between the pores and the oxygen-containing functional groups. Based on the above analysis, water molecule adsorption mechanism models of lignite and coke were constructed. This study offers a new approach for investigating the water molecule adsorption and adsorption mechanisms of lignite and coke.

Moisture induced straining of the cellulosic microfibril

Moisture absorption in the cell wall structure of wood is well known to induce considerable swelling of the wood exerting high expansion forces. This swelling is mainly induced by the sorptive action of the hydroxyl groups of the carbohydrate wood polymers; cellulose and hemicelluloses. On the ultrastructural level, there are, however, still questions with regard to the detailed deformations induced by this moisture absorption. Here, FTIR spectroscopy and synchrotron-radiation-based X-ray diffraction were used on paper samples to study the deformation of the cellulose crystals as a consequence of moisture absorption and desorption. Both techniques revealed that the moisture absorption resulted in a transverse contraction of the cellulose crystals accompanied by a somewhat smaller elongation in the cellulose chain direction. The deformations were found to be a direct response to the increased moisture content and were also found to be reversible during moisture desorption. It is hypothesised that these deformations are a consequence of the swelling forces created by the combined longitudinal and lateral expansions of the non-crystalline cellulose molecules and the glucomannan hemicellulose aligned along the cellulose crystals. These forces will impose a lateral contraction of the cellulose crystals, as well as a longitudinal extension of it. Graphic abstract

Thermodynamics of moisture sorption in tobacco (Nicotiana tabacum L.) seeds

In this study, the thermodynamic characteristics of tobacco seeds were investigated, based on experimental data from equilibrium moisture isotherms at desorption. An empirical exponential relationship was found for the decrease of the net isosteric heat and the differential entropy, based on the Clausius-Clapeyron equation, in response to the increase in moisture content; the values of the two parameters varied from 31.09 to 1.46 kJ.mol-1 and from 91.53 to 4.29 J.mol-1.K-1, respectively. The linear relationship between the enthalpy and the entropy in the moisture desoption of tobacco seeds supported the validity of the enthalpy-entropy theory. The value of Gibbs free energy was positive and the harmonic temperature (297.5 K) was lower than the isosteric temperature (339.6 K). The outcomes from the study provide for the deeper insight into the process of moisture desorption of tobacco seeds.

Thermodynamic properties of moisture desorption isotherms of ryegrass (Lolium multiflorum L.) seeds

ABSTRACT Studies about the thermodynamic properties of ryegrass seeds are necessary to improve post-harvest processes, relating the factors that affect product quality with the interaction between water and its chemical components. Given the importance of recognizing and understanding the intrinsic behavior of water in ryegrass seeds and providing data for the improvement of industrial drying equipment, this work aimed to calculate and evaluate the thermodynamic properties of moisture desorption of ryegrass seeds as a function of the equilibrium moisture content. Ryegrass seeds with initial moisture content of 10.4 (% d.b.) was used. The equilibrium moisture content of seeds was determined by static-gravimetric method at different temperatures (10, 20, 30, 40, and 50 °C) and water activity values (between 0.10 and 0.90), in three repetitions. The Chung Pfost model presented the best fit to the experimental data. It was observed that the integral isosteric desorption heat increased as the equilibrium moisture content decreased, ranged from 2499.95 to 4241.96 kJ kg-1 in the moisture content range 2.80 to 22.10 (% d.b.). Differential entropy also increased with decreasing equilibrium moisture content, as did Gibbs free energy, being positive for all temperature studied, indicating that ryegrass seeds desorption is a non-spontaneous process. The enthalpy-entropy compensation theory was satisfactorily applied to the sorption phenomenon, being controlled by enthalpy.

Contribution of cellulosic fibre filter on atmosphere moisture content in laser powder bed fusion additive manufacturing

Cellulosic materials are commonly used to manufacture the particulate filters used in laser powder bed fusion (LPBF) additive manufacturing (AM) equipment. An experimental approach has been used to calculate the moisture quantity and kinetics of sorption in a cellulosic filter at varying relative humidity (RH) levels. A prediction of the amount of moisture which can be theoretically held within a filter during storage before its use has been obtained. Subsequently, the quantity and the rate of moisture desorption which can be transferred into the build chamber during LPBF is presented. This work highlights the importance of filter storage and conditioning prior to use in additive manufacturing processing.

Frequency-dependent viscoelastic properties of Chinese fir (Cunninghamia lanceolata) under hygrothermal conditions. Part 2: moisture desorption

The frequency-dependent viscoelasticity of Chinese fir (Cunninghamia lanceolata) during moisture desorption was investigated and the applicability of the time-moisture superposition (TMS) relation on wood stiffness and damping during the moisture desorption was verified. The hygrothermal conditions for the moisture desorption were set up as six constant temperatures ranging from 30 to 80°C and three relative humidity (RH) levels at 0, 30 and 60%. Due to the elimination of water during the moisture desorption, the stiffness of the Chinese fir increased, whereas the damping decreased. With the increase in frequency, increased stiffness and decreased damping were observed. Utilizing the TMS relation, it was possible to construct master curves of wood stiffness at temperatures ranging from 30 to 80°C. The linear relationship between the shift factor and the moisture content (MC) manifested a low intermolecular cooperativity between the polymers and a narrow relaxation window. However, the TMS relation was not able to predict the wood damping properties during the moisture desorption, because wood is a multi-relaxation system. The non-proportional relationship between the free volume and MC during the moisture desorption may also explain why the TMS relation failed to construct master curves of the wood damping properties.