Humidity dependence of fracture toughness of cellulose fibrous networks.

Cellulose-based materials are increasingly finding applications in technology due to their sustainability and biodegradability. The sensitivity of cellulose fiber networks to environmental conditions such as temperature and humidity is well known. Yet, there is an incomplete understanding of the dependence of the fracture toughness of cellulose networks on environmental conditions. In the current study, we assess the effect of moisture content on the out-of-plane (i.e., z-dir.) fracture toughness of a particular cellulose network, specifically Whatman cellulose filter paper. Experimental measurements are performed at 16% RH along the desorption isotherm and 23, 37, 50, 75% RH along the adsorption isotherm using out-of-plane tensile tests and double cantilever beam (DCB) tests. Cohesive zone modeling and finite element simulations are used to extract quantitative properties that describe the crack growth behavior. Overall, the fracture toughness of filter paper decreased with increasing humidity. Additionally, a novel model is developed to capture the high peak and sudden drop in the experimental force measurement caused by the existence of an initiation region. This model is found to be in good agreement with experimental data. The relative effect of each independent cohesive parameter is explored to better understand the cohesive zone-based humidity dependence model. The methods described here may be applied to study rupture of other fiber networks with weak bonds.

Strong and optically transparent films prepared using cellulosic solid residue recovered from cellulose nanocrystals production waste stream.

We used a new cellulosic material, cellulosic solid residue (CSR), to produce cellulose nanofibrils (CNF) for potential high value applications. Cellulose nanofibrils (CNF) were produced from CSR recovered from the hydrolysates (waste stream) of acid hydrolysis of a bleached Eucalyptus kraft pulp (BEP) to produce nanocrystals (CNC). Acid hydrolysis greatly facilitated homogenization to fibrillate CSR to CNF with only 15 passes in a microfluidizer compared with at least 47 passes to fibrillate BEP to nanofibrils. CNF from CSR were nanowhiskers with a length between 50 and 400 nm and a diameter 3-10 nm with limited aggregation while CNF from BEP were entangled networks of nanofibrils with a length of 500-1000 nm and a diameter of 10-50 nm. CNFs from CSR had good spectral transparency from UV to infrared, i.e, transmittance of CNF-CSR suspensions at 0.1% solids consistency is greater than 90% at wavelengths greater than 340 nm, compared with less than 30% for CNF suspension produced from BEP. Specific tensile strength and modulus of CNF films from CSRs reached 75 kN·m/kg and 12 MN·m/kg, respectively, approximately 175% of the respective values for conventional paper made of refined BEP.

Acquired thoracic scoliosis following minimally invasive repair of pectus excavatum.

The minimally invasive pectus excavatum repair as described by Nuss et al. is rapidly gaining acceptance as an effective method of repair of severe pectus excavatum deformities in the pediatric population. It potentially offers several advantages over previous techniques. The incidence of major complications of the procedure has been reduced by recent modifications including utilization of video-assisted thoracoscopy during placement of the Lorenz pectus bar as well as utilizing the pectus bar stabilizer that provides more rigid fixation of the strut. We report two cases of acquired thoracic scoliosis following minimally invasive repair of severe pectus excavatum deformity. This particular complication has not been reported in previous literature and warrants concern. In both cases the thoracic scoliosis slowly improved with physical therapy and range-of-motion exercises.