Biaxial deformation behavior and mechanical properties of a polypropylene/clay nanocomposite

Polymer nanocomposites offer the potential of enhanced properties such as increased modulus and barrier properties to the end user. Much work has been carried out on the effects of extrusion conditions on melt processed nanocomposites but very little research has been conducted on the use of polymer nanocomposites in semi-solid forming processes such as thermoforming and injection blow molding. These processes are used to make much of today’s packaging, and any improvements in performance such as possible lightweighting due to increased modulus would bring signi?cant bene?ts both economically and environmentally. The work described here looks at the biaxial deformation of polypropylene–clay nanocomposites under industrial forming conditions in order to determine if the presence of clay affects processability, structure and mechanical properties of the stretched material. Melt compounded polypropylene/clay composites in sheet form were biaxially stretched at a variety of processing conditions to examine the effect of high temperature, high strain and high strain rate processing on sheet structure
and properties.

A biaxial test rig was used to carry out the testing which imposed conditions on the sheet that are representative of those applied in injection blow molding and thermoforming. Results show that the presence of clay increases the yield stress relative to the un?lled material at typical processing temperatures and that the sensitivity of the yield stress to temperature is greater for the ?lled material. The stretching process is found to have a signi?cant effect on the delamination and alignment of clay particles (as observed by TEM) and on yield stress and elongation at break of the stretched sheet.

Effect of batch size on mechanical properties of granules in high shear granulation

The flow patterns in a high shear granulator depend on the fill volume. For example, DEM simulations reported by Terashita et al. [1] show that fill volume affects the velocities and kinetic energies of the particles. It also influences the granule size distribution [2]. Here the effects on the properties of the granule are described. The total mass of the granulate material was varied without changing the other variables such as impeller speed, granulation time and liquid to solid ratio. The resulting mechanical properties, such as strength, yield stress and Young's modulus, of the granules were measured. For the materials studied in the current work, increasing the fill factor (batch size) increased the values of these material parameters. This could be explained by the relative increase in the number and intensity of collisions between the particles, when the size of a batch was increased, leading to smaller porosities. (c) 2010 Elsevier B.V. All rights reserved.

Optimisation of rheological parameters and mechanical properties of superplasticised cement grouts containing metakaolin and viscosity modifying admixture

The objective of this research was to optimise the rheological parameters, hardened properties, and setting times of cement grouts containing metakaolin (MTK), viscosity-modifying agent (VMA) and superplasticiser (SP). All mixes were made with water-to-binder ratio (W/B) of 0.40. The replacement of cement by MTK was varied from 6% to 20% (by mass), and dosages of SP and VMA were varied from 0.3% to 1.4%, and 0.01% and 0.06% (by mass of binder), respectively. Increased SP led to an increase in fluidity, reduction in flow time, plate cohesion, rheological parameters, and an increase in the setting times. Increased VMA demonstrated a reduction in fluidity, an increase in Marsh cone time, plate cohesion, yield stress, and plastic viscosity. Results indicate that the use of MTK increased yield stress, plastic viscosity, cohesion plate, and flow time due to the higher surface area associated with an increase in the water demand. MTK reduced mini-slump and setting times, and improved compressive strength.

Mechanical properties and cellular response of novel electrospun nanofibers for ligament tissue engineering: Effects of orientation and geometry

Electrospun nanofibers are a promising material for ligamentous tissue engineering, however weak mechanical properties of fibers to date have limited their clinical usage. The goal of this work was to modify electrospun nanofibers to create a robust structure that mimics the complex hierarchy of native tendons and ligaments. The scaffolds that were fabricated in this study consisted of either random or aligned nanofibers in flat sheets or rolled nanofiber bundles that mimic the size scale of fascicle units in primarily tensile load bearing soft musculoskeletal tissues. Altering nanofiber orientation and geometry significantly affected mechanical properties; most notably aligned nanofiber sheets had the greatest modulus; 125% higher than that of random nanofiber sheets; and 45% higher than aligned nanofiber bundles. Modifying aligned nanofiber sheets to form aligned nanofiber bundles also resulted in approximately 107% higher yield stresses and 140% higher yield strains. The mechanical properties of aligned nanofiber bundles were in the range of the mechanical properties of the native ACL: modulus=158±32MPa, yield stress=57±23MPa and yield strain=0.38±0.08. Adipose derived stem cells cultured on all surfaces remained viable and proliferated extensively over a 7 day culture period and cells elongated on nanofiber bundles. The results of the study suggest that aligned nanofiber bundles may be useful for ligament and tendon tissue engineering based on their mechanical properties and ability to support cell adhesion, proliferation, and elongation.

Processing characteristics and mechanical properties of metallocene catalyzed linear low-density polyethylene foams for rotational molding

The object of this work is to assess the suitability of metallocene catalyzed linear low-density polyethylenes for the rotational molding of foams and to link the material and processing conditions to cell morphology and part mechanical properties (flexural and compressive strength). Through adjustments to molding conditions, the significant processing and physical material parameters that optimize metallocene catalyzed linear low-density polyethylene foam structure have been identified. The results obtained from an equivalent conventional grade of Ziegler-Natta catalyzed linear low-density polyethylene are used as a basis for comparison. The key findings of this study are that metallocene catalyzed LLDPE can be used in rotational foam molding to produce a foam that will perform as well as a ZieglerNatta catalyzed foam and that foam density Is by far the most Influential factor over mechanical properties of foam. © 2004 Society of Plastics Engineers.