Home About us Contact
|
Home About us Contact | ||
|
|
||
Poor Mechanical Properties (poor + mechanical_property)
Selected AbstractsImproving Mechanical Properties of Crystalline Solids by Cocrystal Formation: New Compressible Forms of ParacetamolADVANCED MATERIALS, Issue 38-39 2009Shyam Karki Poor mechanical properties of paracetamol are improved through the strategy of cocrystal formation. Mechanochemical screening by liquid-assisted grinding generated four cocrystals of paracetamol that readily form tablets by direct compression. Computational studies reveal the mechanical properties can be related to structural features, before all the formation of hydrogen-bonded layers. [source] Preparation and properties of ,-chitin-whisker-reinforced hyaluronan,gelatin nanocomposite scaffoldsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Parintorn Hariraksapitak Abstract Tissue scaffolds made of naturally derived polymers present poor mechanical properties, which may limit their actual utilization in certain areas where high strength is a key criterion. This study was aimed at developing tissue scaffolds from a 50 : 50 w/w blend of hyaluronan (HA) and gelatin (Gel) that contained different amounts of acid-hydrolyzed ,-chitin whiskers (CWs) by a freeze-drying method. The weight ratios of the CWs to the blend were 0,30%. These scaffolds were characterized for their physical, physicochemical, mechanical, and biological properties. Regardless of the CW content, the average pore size of the scaffolds ranged between 139 and 166 ,m. The incorporation of 2% CWs in the HA,Gel scaffolds increased their tensile strength by about two times compared to those of the other groups of the scaffolds. Although the addition of 20,30% CWs in the scaffolds improved their thermal stability and resistance to biodegradation, the scaffolds with 10% CWs were the best for supporting the proliferation of cultured human osteosarcoma cells (SaOS-2). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Transforming powder mechanical properties by core/shell structure: Compressible sandJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 11 2010Limin Shi Abstract Some active pharmaceutical ingredients possess poor mechanical properties and are not suitable for tableting. Using fine sand (silicon dioxide), we show that a core/shell structure, where a core particle (sand) is coated with a thin layer of polyvinylpyrrolidone (PVP), can profoundly improve powder compaction properties. Sand coated with 5% PVP could be compressed into intact tablets. Under a given compaction pressure, tablet tensile strength increases dramatically with the amount of coating. This is in sharp contrast to poor compaction properties of physical mixtures, where intact tablets cannot be made when PVP content is 20% or less. The profoundly improved tabletability of core/shell particles is attributed to the formation of a continuous three-dimensional bonding network in the tablet. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4458,4462, 2010 [source] Morphology and High Modulus of Laminated Ultra-Drawn Polyethylene Films with Biaxial Orientation Prepared by Microwave HeatingMACROMOLECULAR MATERIALS & ENGINEERING, Issue 7 2007Mami Azuma Abstract To improve the poor mechanical properties of uniaxially ultra-drawn films along the transverse direction, lamination of two ultrahigh molecular weight polyethylene/ethylene dimethylaminoethyl methacrylate copolymer blend films was carried out in the rectangular elongation direction by a microwave heating method. The characteristics of the successful laminated films were analyzed theoretically and experimentally. The original orientation of the crystallites for the blend films was maintained perfectly after lamination, and the preferential directions intersected each other. The Young's modulus increased symmetrically with respect to the 45 ° direction. This is the first report concerning a drastic improvement of the Young's modulus in the transverse direction for films ultra-drawn along one direction. [source] Dissolution and Enzymatic Degradation Studies Before and After Artificial Ageing of Silk- or Linen-Reinforced Gelatin Laminates, 1MACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2003M. Boyanova Abstract In an attempt to overcome the poor mechanical properties of native, i.e., untreated gelatin, laminates based on gelatin and gelatin/starch blend reinforced with fabrics (linen or silk) were prepared by melt pressing. The mechanical properties of fresh and artificially aged samples were reported previously. In the present series of two consecutive papers we present data concerning the dissolution and biodegradation of these laminates. A two-step procedure for treatment of the laminates was used. The first step is treatment with an aqueous buffer solution, the second with a buffered solution of the enzyme subtilisin. The time-course of the absorbance at 280 nm of the "washing" solutions was followed. A number of kinetic characteristics was determined and discussed with respect to laminate composition and their treatments. In the present Part 1 about the environmental behavior of these new biodegradable materials, the non-enzymatic solubilization in water and buffer solution (i.e., simple dissolution) of fresh and artificially aged samples is described. The dissolution process was followed spectrophotometrically as well as by the weight losses. It was found that gelatin-based silk- or linen-reinforced laminates were subject to dissolution, similarly to the gelatin and gelatin-based materials studied in previous works. In addition, it was established that the thermal treatment of the laminates during their melt pressing leads to postcondensation reactions and crosslinking of the gelatin macromolecules. Similar reactions occur between the matrix and the reinforcing element silk, thus improving their mutual adhesion. Decreased gelatin dissolution ability was observed after the thermal treatment, in the presence of reinforced fabrics and upon "additional" crosslinking with methylenedi(p -phenyl) diisocyanate. The untreated gelatin is the only one that dissolves completely in water. The artificially aged samples tend to dissolve better than the respective fresh samples due to degradation processes during aging. [source] Influence of ionomeric compatibilizers on the morphology and properties of amorphous polyester/polyamide blendsPOLYMER ENGINEERING & SCIENCE, Issue 9 2004Gregory C. Gemeinhardt The utilization of sulfonated polyester ionomers as minor-component compatibilizers in blends of an amorphous polyester and polyamide was investigated. The blends were prepared using twin-screw extrusion and compared to solution blends to investigate the effect of elevated temperatures and shear mixing on blend miscibility and/or phase behavior. The phase domain sizes of the solution blends with respect to ionomer content were studied using small angle light scattering (SALS) and phase contrast optical microscopy. The thermal and mechanical properties of the extruded blends were investigated using dynamic mechanical analysis (DMA) and tensile testing while the morphology was investigated using environmental scanning electron microscopy (ESEM). The interactions between the sulfonate group of the ionomer and the polyamide were characterized using FT-IR spectroscopy. Binary blends of the amorphous polyester and polyamide were immiscible with poor mechanical properties, while blends containing the polyester ionomer as a minor-component compatibilizer showed a significant reduction in the dispersed domain sizes and enhanced ultimate mechanical properties. The compatibilization mechanism is attributed to specific interactions between the sulfonate groups on the polyester ionomer and the amide groups of the polyamide. Polym. Eng. Sci. 44:1721,1731, 2004. © 2004 Society of Plastics Engineers. [source] Injection moldability and properties of compatibilized PA6/LDPE blendsPOLYMER ENGINEERING & SCIENCE, Issue 9 2004L. Canfora An ethylene-acrylic acid copolymer (EAA), either alone or combined with a low molar mass bis-oxazoline compound (PBO), has been used as a compatibilization promoter for blends of polyamide-6 (PA6) with low-density polyethylene (LDPE). The effect of compatibilization on blend processability in injection molding operations and on the properties of the molded specimens has been studied. In the absence of compatibilization, the injection molded articles were shown to have low-quality surface appearance and poor mechanical properties. Both these characteristics were appreciably improved as a result of reactive compatibilization of the blends with EAA and, even more, with the EAA-PBO couple. In fact, the finished articles prepared by injection molding of the quaternary blends were shown to possess good surface appearance, fine and stable morphology and satisfactory mechanical properties. The results confirm the conclusion of a previous study, i.e., that the PBO fourth component may promote the in situ formation of PA6- g -EAA copolymers, by reaction with both the functional groups of PA6 and the carboxyl groups of EAA. Polym. Eng. Sci. 44:1732,1737, 2004. © 2004 Society of Plastics Engineers. [source] Relationship between cell morphology and impact strength of microcellular foamed high-density polyethylene/polypropylene blendsPOLYMER ENGINEERING & SCIENCE, Issue 8 2004Pornchai Rachtanapun Polymer blends, such as those resulting from recycling postconsumer plastics, often have poor mechanical properties. Microcellular foams have been shown to have the potential to improve properties, and permit higher-value uses of mixed polymer streams. In this study, the effects of microcellular batch processing conditions (foaming time and temperature) and HDPE/PP blend compositions on the cell morphology (the average cell size and cell-population density) and impact strength were studied. Optical microscopy was used to investigate the miscibility and crystalline morphology of the HDPE/PP blends. Pure HDPE and PP did not foam well at any processing conditions. Blending facilitated the formation of microcellular structures in polyolefins because of the poorly bonded interfaces of immiscible HDPE/PP blends, which favored cell nucleation. The experimental results indicated that well-developed microcellular structures are produced in HDPE/PP blends at ratios of 50:50 and 30:70. The cell morphology had a strong relationship with the impact strength of foamed samples. Improvement in impact strength was associated with well-developed microcellular morphology. Polym. Eng. Sci. 44:1551,1560, 2004. © 2004 Society of Plastics Engineers. [source] Expansion mechanisms of plastic/wood-flour composite foams with moisture, dissolved gaseous volatiles, and undissolved gas bubbles,POLYMER ENGINEERING & SCIENCE, Issue 7 2003G. M. Rizvi The large quantity of moisture in wood-flour may lead to the deterioration of the cell structure of foamed plastic wood-flour composites in terms of cell size, non-uniformity, and poor surface quality. Since these anomalies can cause poor mechanical properties of the foamed composites, the removal of the moisture from wood-flour becomes a critical issue with respect to the improvement of these properties. The wood-flour in this experimental study was first oven-dried at different temperatures and then subjected to acetone extraction and thermogravimetric analysis (TGA). The oven-dried wood-flour was blended with plastic and then subjected to extrusion foaming. The results obtained from the TGA studies indicate that most volatiles were released from the extractives. Conversely, a comparative experimental study of the foaming behavior of these plastic/wood-flour composites versus that of undried wood-flour composites confirms that removal of the adsorbed moisture from wood-flour results in a better cell morphology. However, it seems that some gaseous emissions released from wood-flour are soluble in plastic and thereby favorably contribute to the development of the cell morphology. This paper describes the expansion mechanisms of wood-flour composite foams resulting from the adsorbed moisture and dissolved gaseous emissions as well as resulting from the finely dispersed undissolved gas bubbles released from a chemical blowing agent. [source] Ejection force modeling for stereolithography injection molding toolsPOLYMER ENGINEERING & SCIENCE, Issue 4 2002Giang T. Pham Stereolithography (SL) molds have proven effective for short injection molding runs. However, they are susceptible to failure because of their poor mechanical properties, especially at elevated temperatures. A majority of these failures occur during the ejection stage, as a result of excessive ejection forces. An ejection force model was developed by combining the effects of thermal shrinkage and mechanical interlocking due to stair-steps on the surface of SL tools. Finite element analyses were performed to validate and complement the ejection force equation. Measured forces and temperatures from injection molding experiments indicated that the ejection force model is valid for SL molds of both circular and non-circular shape. The average differences between measured and predicted ejection forces were approximately 10%. [source] | ||||||||||