Processing parameters optimization of cotton stalk (Gossypium hirsutum L.) particleboards with emulsifiable polymeric isocyanate adhesive

The compaction behavior of cotton stalk particle mats, temperature profile inside the particle mats, and influence of surface particle size were studied relative to the properties of three-layered cotton stalk particleboards. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bond, and thickness swelling were used as a measure for mechanical and physical performance. Two types of cotton stalk particleboard were manufactured. Results indicated that compression stiffness of the particle mat increased with increasing particle size; however, it decreased with increasing mat moisture content and temperature. At mat moisture contents of 12% and 18%, the plateau temperature at the centerline was not significantly different between boards having coarse and fine particles. However, the plateau time of boards with coarse particles was significantly lower than that of boards with fine particles. Additionally, thickness swelling of boards with a surface particle size of 2 mm was significantly lower than that of boards with surface particle size of 4 mm. Boards with a surface particle size of 2 mm had MOR and MOE values 15% and 10% higher, respectively, than boards with surface particle size of 4 mm. Internal bond decreased 6.5% with decreasing surface particle size from 4 mm to 2 mm.

Bio-Polyurethane Resins Derived from Liquid Fractions of Lignin for the Modification of Ramie Fibers

In this study, technical lignin from black liquor was used as a pre-polymer for the preparation of bio-polyurethane (Bio-PU) resins. Briefly, the isolated lignin was fractionated using ethyl acetate (EtAc) and methanol (MeOH). The liquid fractions of lignin, such as lignin-EtAc (L-EtAc) and lignin-methanol (L-MeOH), were mixed with 10% of polymeric isocyanate (based on the weight of liquid fractions) to obtain Bio-PU resins. The isolated lignin, fractionated lignin, and lignin-derived Bio-PU resins were characterized using several techniques. The obtained Bio-PU resins were then used to modify ramie fibers using vacuum impregnation method. Fourier Transform Infrared (FTIR) spectroscopy, Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) revealed that the isolated lignin had quite similar characteristics to the lignin standard. Fractionation of lignin with EtAc and MeOH altered its characteristics. FTIR, DSC, and TGA showed that solid fractions of lignin had similar characteristics to lignin standard and isolated lignin, while the liquid fractions had characteristics from lignin and the solvents. The absorption band of isocyanate (−N=C=O) groups was shifted to 2285 cm−1 from 2240 cm−1 owing to the reaction with the −OH groups in lignin, forming urethane (R−NH−C=O−R) groups at 1605 cm−1 in Bio-PU resins. Thermal properties of Bio-PU resins derived from L-EtAc exhibited greater endothermic reaction compared to Bio-PU-L-MeOH. As a result, the free −N=C=O groups in Bio-PU resins have reacted with –OH groups on the surface of ramie fibers and improved its thermal properties. Modification of ramie fibers with Bio-PU resins improved the fibers’ thermal stability by 15% using Bio-PU-LEtAc for 60 min of impregnation.Keywords: Bio-polyurethane resins, Impregnation, Lignin fractions, Ramie fibers, Thermal stability

Homogenous particleboard made from whole cotton (Gossypium hirsutum L.) stalk agricultural waste: Optimisation of particle size and influence of cotton residue on performance

The objective of this research was to characterize the cotton stalk resource. This paper also focused on the manufacturing of formaldehyde-free particleboards using whole cotton stalk. The effects of opening particle sizes and cotton ball residue ratios on performance properties of manufactured particleboard was assessed. Modulus of rupture (MOR), modulus of elasticity (MOE), internal bond (IB), and thickness swelling (TS) were characterized. Particleboards manufactured from four different opening particle sizes (6, 8, 10, and 20 mm) using an emulsifiable polymeric isocyanate adhesive (eMDI) were investigated. Similarly, the same performance properties were evaluated using four different cotton ball residue ratios (0, 5, 10, and 15 wt%). Results showed that the stem length and diameter of cotton stalks cultivated in Queensland (Australia) vary greatly and range from 160 to 890 mm and 5.03 to 10.88 mm, respectively. The highest weight proportion of the resource is the cotton stem making up 46 wt% of the available resource. The highest average values of MOR, MOE, IB, and the lowest TS were observed for boards with an opening particle size of 8 mm. The cotton ball residues had detrimental effects on the mechanical properties with a decrease in properties observed with increasing cotton ball residue load.

Towards a Deeper Understanding of Creep and Physical Aging Behavior of the Emulsion Polymer Isocyanate

Information of the relaxation behaviors of polymer film is crucial to judge the durability of emulsion polymer isocyanate (EPI) as a structural adhesive for bonding timber-based products. A sequence of tensile creep tests and free volume evaluation of the cured EPI adhesive films during isothermal condition were carried out by dynamic mechanical analysis and positron annihilation lifetime spectroscopy, respectively. It is the first time to explore the creep response and physical aging of the EPI film, as well as associated microstructural evolution. The results indicate that the creep characteristics of the glassy EPI coating intimately depend upon the crosslinker and elapsed time, and the ideal momentary creep master curve can be constructed in terms of modified horizontal shifting method. Furthermore, the relaxation process is found to be dominated by vacancy diffusion mechanism. In addition, increasing the polymeric isocyanate content can significantly enhance the resistance to creep deformation of EPI films, but also accelerate the physical aging process. Due to a higher packing degree of pure polymer films, the EPI films with aqueous emulsified isocyanate exhibit much better relaxation resistance compared to that with general isocyanate crosslinker.

Study on the Chemical Modification of Titanium-Doped Silicone Using Hydroxyl-Terminated Saturated Polyester

In this paper, a kind of titanium-doped silicone prepolymer(TDS) was modified by hydroxyl-terminated saturated polyester (HTSP) by condensation polymerization. By Fourier Transform Infrared Spectroscopy (FTIR) the reaction of ethoxy groups of the TDS prepolymer with hydroxyl groups of the HTSP during condensation polymerization process was confirmed. The resins were cured with blocked polymeric isocyanate. The influence of the HTSP content on the properties of the modified resins such as thermal stability, corrosion resistance, as well as mechanical and other properties, were discussed in detail. The results showed that the properties of the resins were improved greatly after modification, and the optimal mass ratio of TDS to HTSP in the modified resins was 1:1. Thermogravimetry analysis (TGA) studies indicated that the weight loss of this sample（wTDS : wHTSP =1:1） was not obviously below 400°Cand the impedance value of this coating was significantly higher than that of the others.