Fracture Energy and Critical Strength of High Molecular Weight Glassy Polymers

1990 ◽  
Vol 214 ◽  
Author(s):  
Antonios G. Mikos ◽  
Nikolaos A. Peppas
Keyword(s):  
Molecular Weight ◽  
Fracture Energy ◽  
Molecular Model ◽  
Mesh Size ◽  
Glassy Polymers ◽  
Segment Length ◽  
Critical Strength ◽  
Theoretical Predictions ◽  
Entanglement Network ◽  
Chain Entanglements

ABSTRACTThe fracture energy and the critical strength of glassy polymers with molecular weight larger than the critical value for the onset of chain entanglements are proportional to the number of chain segments entangled about a unit plane. A new molecular model is presented to calculate the crossing density of these chain segments when the segment length is a stochastic variable. The crossing density depends on the mesh size of the entanglement network and the number of entanglement network strands per unit volume. Theoretical predictions of the variation of the fracture energy and strength with the molecular weight are compared with experimental results for various glassy polymers.

scholarly journals Crazing and yielding in glassy polymers of high molecular weight

Polymer ◽  
2020 ◽  
Vol 197 ◽  
pp. 122445 ◽  
Author(s):  
Masoud Razavi ◽  
Shiwang Cheng ◽  
Da Huang ◽  
Shufan Zhang ◽  
Shi-Qing Wang
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Glassy Polymers

scholarly journals Controlling Fluid Diffusion and Release through Mixed-Molecular-Weight Poly(ethylene) Glycol Diacrylate (PEGDA) Hydrogels

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3381 ◽  
Author(s):  
Kieran O’Donnell ◽  
Adrian Boyd ◽  
Brian J. Meenan
Keyword(s):  
Tissue Engineering ◽  
Molecular Weight ◽  
Ethylene Glycol ◽  
Mesh Size ◽  
Material Structure ◽  
Poly Ethylene Glycol ◽  
Glycol Diacrylate ◽  
Fluorescence Measurements ◽  
Fluid Permeability ◽  
Poly Ethylene

Due to their inherent ability to swell in the presence of aqueous solutions, hydrogels offer a means for the delivery of therapeutic agents in a range of applications. In the context of designing functional tissue-engineering scaffolds, their role in providing for the diffusion of nutrients to cells is of specific interest. In particular, the facility to provide such nutrients over a prolonged period within the core of a 3D scaffold is a critical consideration for the prevention of cell death and associated tissue-scaffold failure. The work reported here seeks to address this issue via fabrication of hybrid 3D scaffolds with a component fabricated from mixed-molecular-weight hydrogel formulations capable of storing and releasing nutrient solutions over a predetermined time period. To this end, poly(ethylene) glycol diacrylate hydrogel blends comprising mixtures of PEGDA-575 Mw and PEGDA-2000 Mw were prepared via UV polymerization. The effects of addition of the higher-molecular-weight component and the associated photoinitiator concentration on mesh size and corresponding fluid permeability have been investigated by diffusion and release measurements using a Theophylline as an aqueous nutrient model solution. Fluid permeability across the hydrogel films has also been determined using a Rhodamine B solution and associated fluorescence measurements. The results indicate that addition of PEGDA-2000 Mw to PEGDA-575 Mw coupled with the use of a specific photoinitiator concentration provides a means to change mesh size in a hydrogel network while still retaining an overall microporous material structure. The range of mesh sizes created and their distribution in a 3D construct provides for the conditions required for a more prolonged nutrient release profile for tissue-engineering applications.

scholarly journals Microstructure and Mechanical/Elastic Performance of Biobased Poly (Butylene Furanoate)–Block–Poly (Ethylene Oxide) Copolymers: Effect of the Flexible Segment Length

Polymers ◽  
2020 ◽  
Vol 12 (2) ◽  
pp. 271 ◽  
Author(s):  
Magdalena Kwiatkowska ◽  
Inez Kowalczyk ◽  
Konrad Kwiatkowski ◽  
Agata Zubkiewicz
Keyword(s):  
Molecular Weight ◽  
Phase Separation ◽  
Ethylene Oxide ◽  
Mechanical Performance ◽  
Elastic Recovery ◽  
Segment Length ◽  
Poly Ethylene Oxide ◽  
Injection Molded ◽  
Poly Ethylene ◽  
Flexible Segment

The aim of this paper is to extend knowledge on biobased poly(butylene furanoate)–block–poly (ethylene oxide) (PBF-b-PEO) copolymers’ performance by studying the effect of the PEO segment’s molecular weight on the microstructure and materials behavior. As crystallization ability of PEO depends on its molecular weight, the idea was to use two PEO segment lengths, expecting that the longer one would be able to crystallize affecting the phase separation in copolymers, thus affecting their mechanical performance, including elasticity. Two series of PBF-block-PEOs with the PEO segments of 1000 and 2000 g/mol and different PBF/PEO segment ratios were synthesized by polycondensation in melt, injection molded to confirm their processability, and subjected to characterization by NMR, FTIR, DSC, DMTA, WAXS, TGA, and mechanical parameters. Indeed, the PEO2000 segment not only supported the crystallization of the PBF segments in copolymers, but at contents at least 50 wt % is getting crystallizable in the low temperature range, which results in the microstructure development and affects the mechanical properties. While the improvement in the phase separation slightly reduces the copolymers’ ability to deformation, it is beneficial for the elastic recovery of the materials. The investigations were performed on the injection molded samples reflecting the macroscopic properties of the bulk materials.

Effects of Hydroxyl Groups Versus Physical Entanglements on the Electrospinning Behavior of Wheat Protein

2007 ◽  
Vol 1 (1) ◽  
pp. 31-36 ◽  
Author(s):  
Dara L. Woerdeman ◽  
Suresh Shenoy ◽  
Dee Breger
Keyword(s):  
Molecular Weight ◽  
Protein Interactions ◽  
Vinyl Alcohol ◽  
Wheat Gluten ◽  
Fiber Formation ◽  
Poly Vinyl Alcohol ◽  
Hydroxyl Groups ◽  
Scanning Electron Micrographs ◽  
Gluten Protein ◽  
Chain Entanglements

The present work investigates the effects of hydroxyl end groups on the electrospinning behavior of wheat gluten protein. We focus upon the impact of both a low molecular weight additive (a star-branched polyol: ethoxylated trimethylolpropane) and a high molecular weight additive (a synthetic biodegradable polymer: poly(vinyl alcohol) on the ability to form electrospun fibers from wheat gluten. The presence of the star-branched polyol in the system appears to impede the formation of molecular entanglements and intermolecular disulfide bridges required for fiber formation, while the addition of poly(vinyl alcohol) (PVOH) to the system leads to a significant increase in the overall number of physical chain entanglements required for fiber formation. The mechanical testing data support the overriding importance of physical chain entanglements as larger amounts of PVOH are combined with wheat gluten. The tensile strength of the wheat gluten-based electrospun fibrous mats, which, increased by an order of magnitude upon adding 13% (w/w) PVOH to the electrospinning solution, resulted in a rapid increase in the measured toughness at 26% (w/w) PVOH. The corresponding scanning electron micrographs reveal that the addition of PVOH to the gluten system results in the formation of flat, ribbonlike fibers. Dough mixograms were also collected to further elucidate the effect of additional hydroxyl groups on the interactions between the gluten protein chains. Evidence reveals that in the high-concentration, doughy regime, a small fraction of the protein–water interactions are replaced by favorable polyol–protein interactions; however, in the dilute-concentration regime, these favorable polyol–protein interactions appear to develop at the expense of disulfide bond formation, a requirement for obtaining fibers via electrospinning.

Strain gradient plasticity effect in indentation hardness of polymers

1999 ◽  
Vol 14 (10) ◽  
pp. 4103-4110 ◽  
Author(s):  
Arthur C. M. Chong ◽  
David C. C. Lam
Keyword(s):  
Strain Gradient ◽  
Glassy Polymers ◽  
Strain Gradient Plasticity ◽  
Indentation Hardness ◽  
Gradient Plasticity ◽  
Force Microscopy ◽  
Atomic Force ◽  
Plasticity Effect ◽  
Theoretical Predictions ◽  
Thermosetting Epoxy

Plasticity in material is typically described as a function of strain, but recent observations from torsion and indentation experiments in metals suggested that plasticity is also dependent on strain gradient. The effects of strain gradient on plastic deformation in thermosetting epoxy and polycarbonate thermoplastic were experimentally investigated by nanoindentation and atomic force microscopy in this study. Both thermosetting and thermoplastic polymers exhibited hardening as a result of imposed strain gradients. Strain gradient plasticity theory developed on the basis of a molecular kinking mechanism has predicted strain gradient hardening in polymers. Comparisons made between indentation data and theoretical predictions correlated well. This suggests that strain gradient plasticity in glassy polymers is determined by molecular kinking mechanisms.

Consideration of Gustafsson's proposed Eurocode 5 failure criterion for notched timber beams

1993 ◽  
Vol 20 (6) ◽  
pp. 1030-1036 ◽  
Author(s):  
Ian Smith ◽  
Gerret Springer
Keyword(s):  
Fracture Energy ◽  
Key Words ◽  
Failure Criterion ◽  
Structural Design ◽  
Complete Solution ◽  
Design Criterion ◽  
Design Codes ◽  
Beam Design ◽  
Theoretical Predictions ◽  
Timber Beams

Experimental results and theoretical predictions for failure of timber beams with end notches, or cuts on the tension face, are discussed. The validity of Gustafsson's formula and the underlying assumptions are examined in the context of structural design codes. Attention is drawn to the arbitrary dependence of theoretical predictions on the load and geometric arrangement of specimens, and the method by which fracture energy is estimated. It is not intended at this stage to give a complete solution for the problem, but it is concluded to be premature to incorporate the proposed Eurocode 5 failure criterion for notched beams into the Canadian Standard CAN/CSA 086.1. Key words: timber, fracture, notched beam, design criterion.

scholarly journals Chain entanglements and fracture energy in interfaces between immiscible polymers

2003 ◽  
Vol 119 (15) ◽  
pp. 8140-8149 ◽  
Author(s):  
Leonardo Silvestri ◽  
Hugh R. Brown ◽  
Stefano Carrà ◽  
Sergio Carrà
Keyword(s):  
Fracture Energy ◽  
Immiscible Polymers ◽  
Chain Entanglements

scholarly journals Preparation of Associative Polyurethane Thickener and Its Thickening Mechanism Research

2015 ◽  
Vol 2015 ◽  
pp. 1-7 ◽  
Author(s):  
Gao Nan ◽  
Zhang Zhuo ◽  
Dong Qingzhi
Keyword(s):  
Molecular Weight ◽  
Particle Size ◽  
Soft Segment ◽  
Synthesis Process ◽  
Segment Length ◽  
Solvent Ratio ◽  
Aqueous Dispersions ◽  
Before And After ◽  
Size And Morphology ◽  
End Capping

Associative polyurethane (PU) thickener has been synthesized by preparing the prepolymer with the reaction of polyethylene glycol (PEG) and isophorone diisocyanate (IPDI), which then end-capping with long-chain alkanol. The synthesis process, as well as hydrophilic chain length, theoretical molecular weight, solvent ratio, and thickener percentages, has been researched. The results shows that it reaches the upmost thickening effect when the theoretical molecular weight is under 20000, soft-segment length is under 4000, solvent ratio is 1 : 1, and thickener percentages are controlled at 10%. Furthermore, thickening mechanism of PU thickener has been analyzed detailedly through the measurement of the critical micelle concentration (CMC) of PU thickener and analysis of the influence of PU thickener on the particle size and morphology of PU dispersions. It has been observed from the scanning electron microscopy (SEM) that the PU aqueous dispersions produce a certain degree of flocculation when the PU thickener was added, and this flocculation structure has been proved to be a thixotropic structure through the characterization of the change of particle size before and after the thickener is introduced into the PU aqueous dispersions. The CMC measurement results present that the thickening effect will be apparent when the concentration is controlled in a low range.

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