Compression behavior

Compressive Behavior. The most kiformative data ki characterising the compressive behavior of a flexible foam are derived from the entire load-deflection curve of 0—75% deflection and its return to 0% deflection at the speed experienced ki the anticipated appHcation. Various methods have been reported (3,161,169—172) for relating the properties of flexible foams to desked behavior ki comfort cushioning. Other methods to characterize package cushioning have been reported. The most important variables affecting compressive behavior are polymer composition, density, and cell stmcture and size. 

Various geometric coring patterns ki polyurethanes (171,175) and ki latex foam mbber (176) exert significant influences on thek compressive behavior. A good discussion of the effect of cell size and shape on the properties of flexible foams is contained ki References 60 and 156. The effect of open-ceU content is demonstrated ki polyethylene foam (173). 

The curves for 3M XP251S fiberglass-epoxy are shown in Figures C-1 through C-5 [C-1]. Curves are given for both tensile and compressive behavior of the direct stresses. Note that the behavior in the fiber direction is essentially linear in both tension and compression. Transverse to the fiber direction, the behavior is nearly linear in tension, but very nonlinear in compression. The shear stress-strain curve is highly nonlinear. The Poisson s ratios (not shown) are essentially constant with values v.,2 =. 25 and V21 =. 09. 

Yin et al. [73,74] prepared new microgel star amphiphiles and stndied the compression behavior at the air-water interface. Particles were prepared in a two-step process. First, the gel core was synthesized by copolymerization of styrene and divinylbenzene in diox-ane using benzoylperoxide as initiator. Microgel particles 20 run in diameter were obtained. Second, the gel core was grafted with acrylic or methacryUc acid by free radical polymerization, resulting in amphiphilic polymer particles. These particles were spread from a dimethylformamide/chloroform (1 4) solution at the air-water interface. tt-A cnrves indicated low compressibility above lOmNm and collapse pressnres larger than 40 mNm With increase of the hydrophilic component, the molecnlar area of the polymer and the collapse pressure increased. 

The compressive behavior of a DL is a very important mechanical property. Therefore, to study the mechanical properties of various diffusion materials (carbon cloths, carbon fiber papers, and carbon felts), Escribano et al. [251] used a compression cell. The sample diffusion materials were placed between the two plates of the cell, and the thickness and deflection of each sample were measured as a function of the compression pressure. These researchers... 

Bibo, G.A. and Hogg, P.J. (1996). A view, the role of reinforcement architecture on impact damage mechanisms and post-impact compression behavior. J. Muter. Sci. 31, 1115-1137. 

The testing procedures used in this work have all been well described in the literature (4) and are focused on understanding the compression behavior of the powder samples and the mechanical properties of the resulting compacts. These methods are summarized in Table 1. For brevity, we have limited our initial studies to single component systems, but recognize that more work is needed in the future to understand the complex behavior of multicomponent mixtures. The current work should provide a sound basis for further work on such systems. It is intended that this treatise will enable pharmaceutical formulation scientists to better understand the similarities and differences between the most common grades and types of excipients, and will facilitate the rational selection of excipients for use in the development of immediate release tablet formulations. 

Joiris E, Di Martino P, Bermeron C, Guyot-Hermann AM, Guyot JC. Compression behavior of orthorhombic paracetamol. Pharma Res 1998 15 1122-1130. 

Very few examples of heat capacity or compressibility behavior of the type shown in the second column have been observed experimentally, however. Instead, these two properties most often are observed to diverge to some very large number at Tt as shown in the third column of Figure 13.1.1 The shapes of these curves bear some resemblance to the Greek letter, A, and transitions that exhibit such behavior have historically been referred to as lambda transitions. 

Fiszman, S. M., Costell, E., and Duran, L. (1986). Effects of the addition of sucrose and cellulose on the compression behavior of carrageenan gels. Food Hydrocoil. 1 113-120. 

The parameters of the fitted plane (time plasticity d, pressure plasticity e, and twisting angle co) were also exhibited in a 3D plot and this plot is called the 3D parameter plot. This plot exhibits the compression behavior of the powder. It gives a simple yet characteristic description of the tableting properties An example is given in Figure 19b. 

Otsuka, M., Sato, M., and Matsuda, Y. (2001), Comparative evaluation of tableting compression behaviors by methods of internal and external lubricant addition Inhibition of enzymatic activity of trypsin preparation by using external lubricant addition during the tableting compression process, AAPS PharmSci, 3(3), article 20. 

The compression cycle profiles may be used to characterize the consolidation mechanisms of powders as they help to characterize the extent of pressure distribution within the powder bed as well as the formed tablet. The compression behavior... 

Lin, C. Cham, T. Compression behavior and tensile strength of heat-treated polyethylene glycols. Int. J. Pharm. 1995, 118, 169-179. 

Hersey, J.A. Rees, J.E. The effect of particle size on the consohdation of powders during compaction, proceedings from the 2nd, Particle Size Analysis Conference Society for Analytical Chemistry Bradford, UK, 1970, 33-41. York, P. Pilpel, N. The tensile strength and compression behavior of lactose, four fatty acids and their mixtures in relation to tableting. J. Pharm. Pharmacol. 1973, 25 (12 suppl), IP-llP. 

Tablets. SEM was widely used to investigate the structure of tablets. An excellent review is presented by Hess. " Imaging of tablets is a useful tool to demonstrate differences in compression behavior of substances. Fig. 24 shows an example where the plastically deforming spray-dried sorbitol instant was compressed together with the more brittle ascorbic acid in one tablet. At low compressional force of 5 kN for a 10 mm tablet, the rectangular ascorbic acid crystals as well as the partially deformed sorbitol particles are visible (Fig. 24A). In Figs. 24A and B, the surfaces of two tablets compressed at 5 kN and 30 kN are compared. At higher compressional forces, a uniform, flat, and smooth tablet surface is formed, but within this surface a single unchanged ascorbic acid crystal could be detected. Observation of a broken tablet (Fig. 24C), which was prepared at a high compressional force of 30 kN, reveals that the ascorbic acid crystal is totally fixed within a matrix of plastically...

The quality of a compressed tablet is determined by material fill characteristics and compression behavior. During compression, the rate at which tablets can be produced can be limited due to non-uniform material fill characteristics. Pending successful and reproducible material fill (die fill), the powder mass must form a coherent compact that stays intact upon ejection out of the die. Therefore, tablet press performance can be limited due to poor fill characteristics and/or poor compression behavior. 

Malamataris S, Karidas T, Goidas P. Effect of particle size and sorbed moisture on the compression behavior of some hydroxypropyl methylcellulose (HPMC) polymers. Int ] Pharm 1994 103 205-215. 

Johansson B, Wikberg M, Ek R, et al. Compression behavior and crunpactability of microcrystalline cellulose pellets in relationship to their pore structure and mechanical properties. Int J Pharm 1995 117 57-73. 

The sawtooth waveform can be augmented to create a trapezoidal profile. Like the sawtooth profile, the trapezoidal profile uses constant compression and decompression rates. However, between the compression and decompression segments an intentional dwell time is incorporated. The dwell time is often defined as the time that the moving punches remain stationary at their furthest point of travel. This type of profile is useful when studying either the effects of compression rate or dwell time on powder compression behavior. 

FIGURE 24 Effiect of particle size and punch velocity on the compression behavior of polyethylene oxide. Source From Ref. 49. 

The most common variables affecting Heckel analysis are the rate and duration of compression, the degree of lubrication, and even the size and shape of the dies and punches (86) hence these variables should be taken into consideration during analysis. Although the use of the Heckel relationship to study the compression behavior of pharmaceutical powders/granules has been criticized (81), it still remains one of the most commonly used methods in the field of formulation research and development of pharmaceutical solids. 

The use of first order down-winding (i.e., 4>(r) = 2r) in regions of high resolution curvature leads to an over-compressive behavior in smooth regions that may be responsible for artificial steepening of what should be weak gradients. 

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