Decohesion of a polyolefin overlay from a substrate high density polyethylene layer by impact induced stress waves

High-density polythene (HDPE) is difficult to separate from food packaging waste for recycling because the packaging occasionally has multilayer plastic labels attached. Solvents are employed in the current separation techniques to remove undesirable layers from HDPE substrates. The possibility of separating HDPE via the impact-delamination phenomenon was explored both theoretically and experimentally. Using the cohesive zone model (CZM), the decohesion of layers in a model two-layer laminate made of HDPE and LDPE layers was studied theoretically. According to this study, stress waves emerge and severely damage the adhesion between the layers as a cutting blade strikes the laminate at speeds greater than 40 m/s. The damage can be enhanced by increasing the strike velocity and the apex radius of the blade. These findings show that a novel plastic delaminator that can cut and delaminate the laminates simultaneously can be designed. The proposed machine will feature two sets of blades with varying edge apex radii. One set of blades can be designed to cause the most adhesion damage while the other blades cut the laminate. This unique combination of cutting and delamination operations has several benefits, including less solvent waste and downstream processes, greater environmental friendliness, and faster HDPE separation. Laminates from HDPE milk bottles were cut using a high-speed cutter-blender with six blades to test the predicted results. The cut HDPE flakes were separated pneumatically. According to FTIR analysis and SEM, only a trace of adhesive was present on the cut and separated HDPE flakes.

Pressure and stress transients in autoinjector devices

Spring-actuated autoinjectors delivering viscous drug solutions resulting from large drug concentrations require large spring forces which can create high peak pressures and stresses within syringes. The high peak pressures and stresses can lead to device failure. Measurements with a suite of novel instrumentation and analysis using numerical simulation explain the peak pressures and peak stresses as originating from mechanical impacts between moving components, the large acceleration of the components, and surprisingly, the production of tension waves in the liquid resulting in cavitation. The presence and intensity of cavitation depend on relative timing between the pressurization and the acceleration of the syringe, which, in turn, depend on the size and location of an air gap inside the syringe. We show that production of localized but very high pressures can result from shock wave focusing in the conical section of the syringe.

Effects of Stone Size on the Comminution Process and Efficiency in Shock Wave Lithotripsy

The effects of stone size on the process and comminution efficiency of shock wave lithotripsy (SWL) were investigated in experiments, numerical simulations and scale analysis. Cylindrical BegoStone phantoms with approximately equal height and diameter of either 4, 7 or 10 mm, in a total aggregated mass of about 1.5 g, were treated in an electromagnetic shock wave lithotripter field. The resultant stone comminution was found to correlate closely with the average peak pressure, P_+(avg), incident on the stones. The P_+(avg) threshold necessary to initiate stone fragmentation in water increased from 7.9 to 8.8 to 12.7 MPa, respectively, as stone size decreased from 10 to 7 to 4 mm. Similar changes in the P_+(avg) threshold were observed for the 7- and 10-mm stones treated in 1,3-butanediol, in which cavitation is suppressed, suggesting that the observed size dependency is due to changes in stress distribution within stones of different size. Moreover, the slope of the correlation curve between stone comminution and ln(P¯_+(avg)) in water increased with decreasing stone size, whereas the opposite trend was observed in 1,3-butanediol. The progression of stone comminution in SWL exhibited size-dependence: the 7- and 10-mm stones fragmented into progressively smaller pieces, whereas a significant portion (>30%) of the 4-mm stones reached a stalemate within the size range of 2.8 ∼ 4 mm, even after 1000 shocks. Analytical scaling considerations suggest size-dependent fragmentation behavior, a hypothesis further supported by numerical model calculations that reveal changing patterns of constructive and destructive wave interference and, thus, variations in the maximum tensile stress or stress integral produced in cylindrical and spherical stone of different sizes.

A report of three cases and review of the literature on rectal disruption following abdominal seatbelt trauma

Seatbelt associated blunt trauma to the rectum is a rare but well recognised injury. The exact mechanism of hollow visceral injury in blunt trauma is unclear. Stress and shear waves generated by abdominal compression may in part account for injury to gas containing structures. A 'seatbelt sign' (linear ecchymosis across the abdomen in the distribution of the lap belt) should raise the suspicion of hollow visceral injuries and can be more severe with disruption of the abdominal wall musculature. Three consecutive cases of rectal injury following blunt abdominal trauma, requiring emergency laparotomy and resection, are described. Lumbar spine injury occurred in one case and in the other two cases, there was injury to the iliac wing of the pelvis; all three cases sustained significant abdominal wall contusion or muscle disruption. Abdominal wall reconstruction and closure posed a particular challenge, requiring a multidisciplinary approach. The literature on this topic is reviewed and potential mechanisms of injury are discussed.