scholarly journals Factors influencing mechanical properties of polyurethane foams used in compressible flexographic sleeves

2020 ◽  
Author(s):  
Saša Petrović ◽  
◽  
Nemanja Kašiković ◽  
Željko Zeljković ◽  
Rastko Milošević ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Polyurethane Foams ◽  
Compression Testing ◽  
Foam Layer ◽  
Cyclic Compression ◽  
Factors Influencing ◽  
Pu Foam ◽  
Flexographic Printing ◽  
Creep And Stress Relaxation

Polyurethanes are a group of polymers which are in many ways different from other types of plastic. They are used in many different areas due to the fact that many different chemicals can be used during their synthesis, resulting in a variety of structures. Sleeves are comprised of hard base often covered with compressible polyurethane (PU) foam layer. PU foam layer can have different composition and level of porosity which are the main factors influencing compressibility of the sleeve and therefore its area of use. Sleeves are also one of the least researched components in the flexographic printing process. However, mechanical properties of the polyurethane, its fatigue, lifespan and parameters influencing all of them have been extensively investigated in different areas and for different types and formulations of polyurethane. The aim of this paper is to investigate factors influencing mechanical properties of polyurethane foams used in compressible flexographic sleeves. Investigated parameters are foam density, level of strain and strain rate, influence of microstructure under different conditions and parameters influencing creep and stress relaxation. The review of the existing literature regarding mechanical properties of the PU foams makes it possible to select the parameters with the greatest possible influence on the flexographic printing process, as well as to find the most suitable methods to investigate the effect of exploitation on sleeve properties. As a large number of parameters influencing PU foam mechanical properties are fixed during printing, it can be concluded, through the review of the existing literature, that the main parameters to be investigated are the resilience of the sleeve compressible layer during cyclic compression testing (residual strain), maximum stress, Young’s modulus, hysteresis loss, and creep and stress relaxation during cyclic compression testing with strain retention.

The Relation Between Collagen Fibril Kinematics and Mechanical Properties in the Mitral Valve Anterior Leaflet

2006 ◽  
Vol 129 (1) ◽  
pp. 78-87 ◽  
Author(s):  
Jun Liao ◽  
Lin Yang ◽  
Jonathan Grashow ◽  
Michael S. Sacks
Keyword(s):  
Mechanical Properties ◽  
Angular Distribution ◽  
Mitral Valve ◽  
Stress Relaxation ◽  
Collagen Fibril ◽  
Biaxial Loading ◽  
Tissue Level ◽  
Collagen Fibrils ◽  
Anterior Leaflet ◽  
Creep And Stress Relaxation

We have recently demonstrated that the mitral valve anterior leaflet (MVAL) exhibited minimal hysteresis, no strain rate sensitivity, stress relaxation but not creep (Grashow et al., 2006, Ann Biomed Eng., 34(2), pp. 315–325;Grashow et al., 2006, Ann Biomed. Eng., 34(10), pp. 1509–1518). However, the underlying structural basis for this unique quasi-elastic mechanical behavior is presently unknown. As collagen is the major structural component of the MVAL, we investigated the relation between collagen fibril kinematics (rotation and stretch) and tissue-level mechanical properties in the MVAL under biaxial loading using small angle X-ray scattering. A novel device was developed and utilized to perform simultaneous measurements of tissue level forces and strain under a planar biaxial loading state. Collagen fibril D-period strain (εD) and the fibrillar angular distribution were measured under equibiaxial tension, creep, and stress relaxation to a peak tension of 90N∕m. Results indicated that, under equibiaxial tension, collagen fibril straining did not initiate until the end of the nonlinear region of the tissue-level stress-strain curve. At higher tissue tension levels, εD increased linearly with increasing tension. Changes in the angular distribution of the collagen fibrils mainly occurred in the tissue toe region. Using εD, the tangent modulus of collagen fibrils was estimated to be 95.5±25.5MPa, which was ∼27 times higher than the tissue tensile tangent modulus of 3.58±1.83MPa. In creep tests performed at 90N∕m equibiaxial tension for 60min, both tissue strain and εD remained constant with no observable changes over the test length. In contrast, in stress relaxation tests performed for 90minεD was found to rapidly decrease in the first 10min followed by a slower decay rate for the remainder of the test. Using a single exponential model, the time constant for the reduction in collagen fibril strain was 8.3min, which was smaller than the tissue-level stress relaxation time constants of 22.0 and 16.9min in the circumferential and radial directions, respectively. Moreover, there was no change in the fibril angular distribution under both creep and stress relaxation over the test period. Our results suggest that (1) the MVAL collagen fibrils do not exhibit intrinsic viscoelastic behavior, (2) tissue relaxation results from the removal of stress from the fibrils, possibly by a slipping mechanism modulated by noncollagenous components (e.g. proteoglycans), and (3) the lack of creep but the occurrence of stress relaxation suggests a “load-locking” behavior under maintained loading conditions. These unique mechanical characteristics are likely necessary for normal valvular function.

scholarly journals Effects of Extractives on Dimensional Stability, Dynamic Mechanical Properties, Creep, and Stress Relaxation of Rice Straw/High-Density Polyethylene Composites

Polymers ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 1176 ◽  
Author(s):  
Huanbo Wang ◽  
Fazhi Lin ◽  
Pingping Qiu ◽  
Tian Liu
Keyword(s):  
Mechanical Properties ◽  
Thermal Expansion ◽  
Stress Relaxation ◽  
Rice Straw ◽  
Dimensional Stability ◽  
High Density Polyethylene ◽  
Dynamic Mechanical Properties ◽  
High Density ◽  
Dynamic Mechanical ◽  
Creep And Stress Relaxation

The removal of rice straw extractives increases the interphase adhesion between rice straw and the high-density polyethylene (HDPE) matrix, while eradicating the inner defects of rice straw/HDPE composites. This study investigated the effect of rice straw extractives removal on the dimensional stability (water uptake and thermal expansion), dynamic mechanical properties, creep, and stress relaxation of rice straw/HDPE composites. Cold water (CW), hot water (HW), and 1% alkaline solution (AL) extraction methods were utilized to remove rice straw extractives. Extracted and unextracted rice straws were mixed with HDPE, maleated polyethylene (MAPE), and Polyethylene wax to prepare composites via extrusion. Removal of rice straw extractives significantly improved the dimensional stability, dynamic mechanical properties, and creep and stress relaxation of rice straw/HDPE composites, with the exception of the thickness swelling of the AL/HDPE and the thermal expansion of the rice straw/HDPE composites. HW/HDPE exhibited the best comprehensive performance.

The Mechanical Properties of the Pittsburgh Coal at Elevated Temperatures

1977 ◽  
Vol 99 (1) ◽  
pp. 192-198 ◽  
Author(s):  
H. D. Shoemaker ◽  
L. Z. Shuck ◽  
R. R. Haynes ◽  
S. H. Advani
Keyword(s):  
Mechanical Properties ◽  
Stress Relaxation ◽  
Ultimate Strength ◽  
Coal Gasification ◽  
Elevated Temperatures ◽  
Superposition Principle ◽  
Shift Function ◽  
Relaxation Properties ◽  
The Face ◽  
Creep And Stress Relaxation

Mechanical properties of coal have been determined in an effort to advance in situ coal gasification technology. Tests and apparatus were developed to evaluate the directional compressive and shear properties of coal at elevated temperatures. Both creep and stress-relaxation experiments were conducted to evaluate the creep compliance and stress-relaxation properties in compression and shear, at temperatures between 75° and 650°F (24° and 343°C), for the face cleat, butt cleat and normal to coalbed orientation, and four different specimen sizes. Stress-strain relations and ultimate strengths were also determined at three different loading rates for these directions and temperatures. A shift function was used to represent the creep and stress relaxation properties as functions of time and temperature. Four- and six-parameter viscoelastic fluid models were used to represent the data over the time-temperature ranges. Shallow and deep mine coal from the Pittsburgh coalbed was tested. The coal was found to have the greatest ultimate strength and elastic moduli at 200°F (93°C) in all directions in both compression and shear, and to be specimen size dependent. The ultimate strength in the normal to coalbed direction was approximately twice that in the face and butt cleat directions at all temperatures. At 575° to 650°F (302° – 343°C), the coal becomes fluidic and is well represented by a four-parameter fluid model. It also obeys the time-temperature superposition principle.

USE OF STARCH SYRUPS IN THE PRODUCTION OF JELLY

2019 ◽  
pp. 457-462
Author(s):  
Kateryna Iorgachova ◽  
Olga Makarova ◽  
Karyne Avetisian
Keyword(s):  
Mechanical Properties ◽  
Carbohydrate Composition ◽  
Foam Layer ◽  
Quality Indices ◽  
Organoleptic Quality ◽  
Physical Chemical

In the presented work the choice of starch syrup for the jelly products production has been substantiated. It was based on the analysis of the starch syrup carbohydrate profiles and recipes of jelly products. The influence of syrup on the rheological and structural-mechanical properties of jelly and aerated masses for a two-layer jelly has been determined. The expediency of polydextrose usage has been demonstrated. Its adding leads to the regulation of the jelly structure and foam layer for the samples with more than 50% of sugar replaced by starch syrup. Depending on the ratio of carbohydrates in jelly it was determined the amount of polydextrose adding of which provides the required firming and prebiotic properties of finish products. The change of physical-chemical, structural-mechanical, and organoleptic quality indices of two-layer jelly with modified carbohydrate composition has been investigated during storage.

A greener and sustainable approach for converting polyurethane foam rejects into superior polyurethane coatings

2019 ◽  
Author(s):  
Chem Int
Keyword(s):  
Mechanical Properties ◽  
Polyurethane Foam ◽  
Sebacic Acid ◽  
Polyurethane Foams ◽  
Hexamethylene Diisocyanate ◽  
Alkali Resistance ◽  
Microwave Reaction ◽  
P Recycling ◽  
Amine Groups ◽  
Green Polymer

Recycling is a crucial area of research in green polymer chemistry. Various developments in recycling are driven by Environmental concerns, interest in sustainability and desire to decrease the dependence on non-renewable petroleum based materials. Polyurethane foams [PUF] are widely used due to their light weight and superior heat insulation as well as good mechanical properties. As per survey carried Polyurethane Foam Association, 12 metric tonnes of polyurethane foam are discharged during manufacturing and/or processing and hence recycling of PUF is necessary for better economics and ecological reasons. In present study, rejects of PUF is subjected to reaction with a diethylene amine in presence of sodium hydroxide [NaOH] as catalyst, as a result depolymerised product containing hydroxyl and amine groups is obtained. Conventional and Microwave reaction for depolymerizing polyurethane foam have been carried, and best results are obtained by Microwave reaction. Further depolymerised product with hydroxyl and amine functionalities are reacted with bis (2-hydroxyethyl terephthalate) [BHET] obtained by recycling polyethylene terephthalate [PET] and sebacic acid, with stannous oxalate [FASCAT 2100 series] as catalyst to obtain Polyester amides. These Polyester amides having hydroxyl and amino groups in excess are cured with isocyanates-hexamethylene diisocyanate biuret [HDI biuret] and isophorone diisocyanate [IPDI] for coating applications. The coated films are characterized using physical, mechanical and chemical tests, which shows comparable physical, mechanical properties but alkali resistance is poor.

scholarly journals Effects of Various Types of Expandable Graphite and Blackcurrant Pomace on the Properties of Viscoelastic Polyurethane Foams

Materials ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1801
Author(s):  
Rafał Oliwa ◽  
Joanna Ryszkowska ◽  
Mariusz Oleksy ◽  
Monika Auguścik-Królikowska ◽  
Małgorzata Gzik ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Chemical Structure ◽  
Oxygen Index ◽  
Polyurethane Foams ◽  
Expandable Graphite ◽  
Ftir Analysis ◽  
Limiting Oxygen Index ◽  
Peak Heat Release Rate ◽  
Physical And Chemical ◽  
Scanning Electron

We investigated the effect of the type and amount of expandable graphite (EG) and blackcurrant pomace (BCP) on the flammability, thermal stability, mechanical properties, physical, and chemical structure of viscoelastic polyurethane foams (VEF). For this purpose, the polyurethane foams containing EG, BCP, and EG with BCP were obtained. The content of EG varied in the range of 3–15 per hundred polyols (php), while the BCP content was 30 php. Based on the obtained results, it was found that the additional introduction of BCPs into EG-containing composites allows for an additive effect in improving the functional properties of viscoelastic polyurethane foams. As a result, the composite containing 30 php of BCP and 15 php of EG with the largest particle size and expanded volume shows the largest change in the studied parameters (hardness (H) = 2.65 kPa (+16.2%), limiting oxygen index (LOI) = 26% (+44.4%), and peak heat release rate (pHRR) = 15.5 kW/m2 (−87.4%)). In addition, this composite was characterized by the highest char yield (m600 = 17.9% (+44.1%)). In turn, the change in mechanical properties is related to a change in the physical and chemical structure of the foams as indicated by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) analysis.

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