The Role of Interfacial Adhesion in Polymer Composites Engineered from Lignocellulosic Agricultural Waste.

This paper presents a comprehensive study about the application of a lignocellulosic agricultural waste, sunflower husk in different polymer composites. Two types of milled sunflower husk with different geometrical factors were incorporated into polypropylene, low-density and high-density polyethylene, polystyrene (PS), glycol-modified polyethylene terephthalate (PETG) and polylactic acid (PLA). The filler content of the composites varied between 0 and 60 vol%. The components were homogenized in an internal mixer and plates were compression molded for testing. The Lewis-Nielsen model was fitted to the moduli of each composite series, and it was found that the physical contact of the filler particles is a limiting factor of composite modulus. Interfacial interactions were estimated from two independent approaches. Firstly, the extent of reinforcement was determined from the composition dependence of tensile strength. Secondly, the reversible work of adhesion was calculated from the surface energies of the components. As only weak van der Waals interactions develop in the interphase of polyolefins and sunflower husk particles, adhesion is weak in their composites resulting in poor reinforcement. Interfacial adhesion enhanced by specific interactions in the interphase, such as π electron interactions for PS, hydrogen bonds for PLA, and both for PETG based composites.

In vivo arthroscopic cartilage stiffness measurement in the knee.

The purpose of this study was to map the biomechanical properties of normal human articular cartilage in vivo. Instantaneous compressive stiffness was measured in the knee articular cartilage of 87 patients. Lateral femoral condyle stiffness (mean +/- SD; 5.12 +/- 1.02 N) was greater than at all other sites and was significantly greater than mean values obtained for the medial femoral condyle (4.8 +/- 1.22 N), medial and lateral trochlea (4.2 +/- 0.92 and 4.6 +/- 1.27 N, respectively), medial and lateral patella (3.1 +/- 0.66 N and 3.3 +/- 1.01 N, respectively), and medial and lateral tibial condyle (2.4 +/- 1.17 N and 3.2 +/- 1.16 N, respectively) for all subjects (P < .05, Wilcoxon signed-rank test). This study enabled comparison measures of suspected degenerative cartilage.