Molecular Degradation of Lubricants in Sliding Elastohydrodynamic Contacts

1975 ◽  
Vol 97 (3) ◽  
pp. 390-395 ◽  
Author(s):  
D. L. Walker ◽  
D. M. Sanborn ◽  
W. O. Winer
Keyword(s):  
Molecular Weight ◽  
Weight Loss ◽  
Small Samples ◽  
Lubricant Degradation ◽  
Shear Rates ◽  
Molecular Weights ◽  
Average Shear ◽  
Bulk Polymers ◽  
Energy Dissipated ◽  
Viscosity Changes

The extent of lubricant degradation in a sliding elastohydrodynamic contact has been investigated. The lubricant was subjected to peak Hertz pressures of approximately 109 N/m2 and average shear rates of 106 to 107 s−1. Hydrocarbon lubricants, bulk polymers and polymer containing hydrocarbon solutions were examined. Small samples (10−8m3) of test lubricant were extracted from the entrance and exit regions of the EHD contact. These samples were then analyzed to determine alterations in the molecular weight distribution. In addition, a microcapillary viscometer was developed to determine viscosity changes. Degradation resulting in up to a 70 percent viscosity loss was found in fluids which had molecular weights of over 1000. High degrees of correlation were found between molecular weight loss, viscosity loss and the energy dissipated in the contact.

Effects of Molecular Weight of Chitosan on the Biodegradability and Thermal Properties of Polybutylene Succinate/Chitosan Composites

2018 ◽  
Vol 775 ◽  
pp. 26-31
Author(s):  
Sukantika Manatsittipan ◽  
Kamonthip Kuttiyawong ◽  
Kazuo Ito ◽  
Sunan Tiptipakorn
Keyword(s):  
Molecular Weight ◽  
Weight Loss ◽  
Thermal Properties ◽  
Water Absorption ◽  
Melting Temperature ◽  
Microbial Degradation ◽  
Decomposition Temperature ◽  
Molecular Weights ◽  
Significant Difference ◽  
Polybutylene Succinate

In this study, the biodegradability and thermal properties the composites of polybutylene succinate (PBS) and chitosan of different molecular weights (Mn = 104,105, and 106 Da) were prepared at chitosan contents of 0-10 wt%. After 10 days of microbial degradation, the results show that the amount of holes from degradation was increased with either decreasing Mn or increasing chitosan contents. However, the size of holes was increased with increasing Mn and chitosan contents. The results from Differential Scanning Calorimeter (DSC) present that the melting temperature (Tm) of PBS was decreased with increasing chitosan contents. Moreover, there was no significant difference between Tm of the composites with different Mn of chitosan. From the TGA thermograms, the decomposition temperature at 10% weight loss (Td10) was decreased with increasing chitosan contents. Moreover, the water absorption of PBS/chitosan composites was increased with increasing Mn and content of chitosan.

scholarly journals High Performance Conditioning Shampoo with Hyaluronic Acid and Sustainable Surfactants

Cosmetics ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 71
Author(s):  
Kelly Yorke ◽  
Samiul Amin
Keyword(s):  
Molecular Weight ◽  
Surface Tension ◽  
Hyaluronic Acid ◽  
High Performance ◽  
Low Cost ◽  
Hair Follicles ◽  
Shear Rates ◽  
Molecular Weights ◽  
Surface Activity Properties ◽  
Alkyl Polyglucoside

Recently, consumers have become invested in more natural and sustainable ingredients contained in personal care products. Unfortunately, cationic surfactants are still heavily relied on as primary conditioning agents in products such as conditioning shampoos because of their ability to cling well to the negatively charged surface of hair follicles. Additionally, sulfates are utilized as cleansing agents because they are highly effective and low cost. The objective of this study is to find a more sustainable formulation for a conditioning shampoo without compromising the desired wet combing, rheological, and surface activity properties. The systems which were investigated contained hyaluronic acid (HA) at a variety of molecular weights and concentrations, in combination with a surfactant, either acidic sophorolipid (ASL) or alkyl polyglucoside (APG), and varying the presence of sodium chloride. A Dia-stron was utilized to test the wet combing force, a rheometer recorded the viscosity at various shear rates, and a tensiometer measured the surface tension of the samples before a visual foaming study was conducted. Molecular weight and concentration seemed to have a large impact on wet combing force, as well as rheology, with the largest molecular weight and concentration producing the lowest friction coefficient and desired rheological profile. The addition of a surfactant significantly aids in the reduction in surface tension and increased foamability. Therefore, the optimal system to achieve the largest reduction in wet combing force, large viscosity with shear-thinning behavior, and relatively low surface tension with decent foaming is composed of 1% HA at 800 kDa, 10% ASL and 1% NaCl. This system shows a viable sulfate-free and silicone-free option that can achieve both conditioning and cleansing.

Rheological Properties of Multichain Polybutadienes

1965 ◽  
Vol 38 (4) ◽  
pp. 893-906 ◽  
Author(s):  
Gerard Kraus ◽  
J. T. Gruver
Keyword(s):  
Molecular Weight ◽  
Branched Polymers ◽  
Linear Polymers ◽  
Newtonian Viscosity ◽  
Zero Shear Viscosity ◽  
Shear Rates ◽  
Molecular Weights ◽  
High Shear Rates ◽  
Long Chain ◽  
Newtonian Behavior

Abstract The introduction of one or two long chain branches into a polybutadiene molecule to form trichain or tetrachain molecules, respectively, leads to profound changes in Theological behavior. At low molecular weights the Newtonian (zero shear) viscosity is decreased relative to a linear polymer of the same molecular weight. At molecular weights exceeding 60,000 (trichain) or 100,000 (tetrachain), the Newtonian viscosity rises rapidly above the corresponding value for a linear polybutadiene. However, non-Newtonian behavior of the branched polymers becomes more pronounced the higher the molecular weights, so that at moderate to high shear rates the viscosity of the branched polymers is uniformly lower than that of linear polymers of identical molecular weight.

Effects of Molecular Structure on Physical Properties of Butyl Rubber

1946 ◽  
Vol 19 (3) ◽  
pp. 552-598 ◽  
Author(s):  
Paul J. Flory
Keyword(s):  
Molecular Structure ◽  
Molecular Weight ◽  
Physical Properties ◽  
Small Samples ◽  
Rational Approach ◽  
Complete Evaluation ◽  
Testing Procedures ◽  
Molecular Weights ◽  
Vulcanized Rubber ◽  
Structural Variables

Abstract The investigation was undertaken in an attempt to establish the fundamental connections between the physical properties of a typical vulcanized rubberlike polymer and its chemical structure. The structural variables to be considered are the molecular weight of the “primary molecules” entering the vulcanizate, their molecular-weight distribution, and the concentration (or frequency) of cross-linkages introduced during vulcanization. The molecular weights of Butyl rubbers were determined by previously established procedures ; the effects of molecular-weight heterogeneity were suppressed by careful fractionation from very dilute solution. An indirect method, based on the theory of gelation and on the observation of critical molecular weight for incipient gelation (partial insolubility) in “vulcanisates” formed when the cross-linking capacity is fixed, was employed to determine the frequency of occurrence of cross-linked units—a quantity not hitherto evaluated in a vulcanized rubber. In representative pure-gum vulcanizates of Butyl the molecular weight per cross-linked unit ranges from about 35,000 to 20,000, depending (inversely) on the diolefin content of the raw rubber. Micro compounding and testing procedures have been devised for evaluating the necessarily small samples ob- tained in fractionation. Complete evaluation of tensile strength, stress-strain characteristics, swelling in solvents, and creep rate can be obtained with as little as 3 grams of rubber. Results are no less reproducible than those obtained with conventional procedures requiring 50 grams or more. A number of rela- tionships between vulcanizate structure and physical properties have been established. The feasibility of a rational approach to the interpretation of properties of rubber vulcanizates in terms of molecular structure has been demonstrated.

Shear Dependence of Viscosity and Molecular Weight Transitions. A Study of Entanglement Effects

1967 ◽  
Vol 40 (2) ◽  
pp. 522-531
Author(s):  
Suresh N. Chinai ◽  
William C. Schneider
Keyword(s):  
Molecular Weight ◽  
Shear Rate ◽  
Polymer Solutions ◽  
Shear Rates ◽  
Molecular Weights ◽  
Critical Molecular Weight

Abstract Flow of concentrated polymer solutions covering molecular weights up to 150,000 was examined at shear rates up to 200,000 sec−1. The viscosity, molecular weight, and shear rate results of previous workers recognizing only single critical molecular weight M*, above which ordinary Bueche entanglements dominated the flow, were compared with our findings in which two distinct critical molecular weights, upper M* and lower M** exist. These results are compared with the theory, and new interpretations are presented.

Rheological Properties of Polybutadienes Prepared by n-Butyllithium Initiation

1965 ◽  
Vol 38 (4) ◽  
pp. 881-892
Author(s):  
J. T. Gruver ◽  
Gerard Kraus
Keyword(s):  
Molecular Weight ◽  
Shear Rate ◽  
Flow Behavior ◽  
Average Molecular Weight ◽  
Polymer System ◽  
Newtonian Flow ◽  
Newtonian Viscosity ◽  
Long Chain Branching ◽  
Shear Rates ◽  
Molecular Weights

Abstract The flow behavior of n-butyllithium-polymerized polybutadienes was investigated as a function of molecular weight, temperature, and shear rate. At low shear rates these polymers exhibit Newtonian flow up to molecular weights of several hundred thousand so that “zero shear” Newtonian viscosities can readily be determined without the risk of long extrapolation. Above 10,000 molecular weight the Newtonian viscosities obey the well-known 3.4 power dependence on weight-average molecular weight. The entanglement spacing molecular weight is estimated at 5600. The temperature dependence of viscosity is substantially independent of molecular weight and shear stress and can be represented analytically by functions proposed in the literature. The apparent activation energy for viscous flow is not constant, but decreases with rising temperature. The flow of the polymers becomes increasingly non-Newtonian with the product of shear rate, molecular weight and Newtonian viscosity. However, the departure from Newtonian behavior is apparently less than for any polymer system whose flow behavior has been described in the literature. The indications are, therefore, that sharp molecular weight distribution and freedom from long chain branching favor Newtonian flow and that the n-butyllithium initiated polybutadienes represent some of the most perfectly linear, narrow distribution polymers known.

Etching of Polymers by Oxygen Plasma

1968 ◽  
Vol 26 ◽  
pp. 408-409
Author(s):  
Virgil Peck ◽  
W. L. Carter
Keyword(s):  
Molecular Weight ◽  
Oxygen Plasma ◽  
Flow Time ◽  
Microscopical Study ◽  
Surface Layers ◽  
Organic Vapors ◽  
Sample Position ◽  
Accuracy Of Measurement ◽  
Bulk Polymers ◽  
Electron Microscopical

Any electron microscopical study of the morphology of bulk polymers has throughout the years been hampered by the lack of any real ability to produce meaningful surface variations for replication. True etching of polymers should show crystalline and amorphous regions in some form of relief. The use of solvents, acids, organic vapors, and inert ion bombardment to etch samples has proved to be useful only in limited applications. Certainly many interpretations of these results are subject to question.The recent use of a radiofrequency (R. F.) plasma of oxygen to degrade and remove organic material with only minor heating has opened a new possibility for etching polymers. However, rigid control of oxygen flow, time, current, and sample position are necessary in order to obtain reproducible results. The action is confined to surface layers; the molecular weight of the polymer residue after heavy etching is the same as the molecular weight of the polymer before attack, within the accuracy of measurement.

Investigation by HPLC of the Catabolism of Recombinant Tissue Plasminogen Activator in the Rat

1988 ◽  
Vol 60 (01) ◽  
pp. 107-112 ◽  
Author(s):  
Roy Harris ◽  
Louis Garcia Frade ◽  
Lesley J Creighton ◽  
Paul S Gascoine ◽  
Maher M Alexandroni ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Plasminogen Activator ◽  
Tissue Plasminogen Activator ◽  
Half Life ◽  
Recombinant Tissue Plasminogen Activator ◽  
Rat Plasma ◽  
High Molecular Weight Complex ◽  
Molecular Weights ◽  
Major Activity ◽  
Tissue Plasminogen

SummaryThe catabolism of recombinant tissue plasminogen activator (rt-PA) was investigated after injection of radiolabelled material into rats. Both Iodogen and Chloramine T iodination procedures yielded similar biological activity loss in the resultant labelled rt-PA and had half lives in the rat circulation of 1 and 3 min respectively. Complex formation of rt-PA was investigated by HPLC gel exclusion (TSK G3000 SW) fractionation of rat plasma samples taken 1-2 min after 125I-rt-PA injection. A series of radiolabelled complexes of varying molecular weights were found. However, 60% of the counts were associated with a single large molecular weight complex (350–500 kDa) which was undetectable by immunologically based assays (ELISA and BIA) and showed only low activity with a functional promoter-type t-PA assay. Two major activity peaks in the HPLC fractions were associated with Tree t-PA and a complex having a molecular weight of ̴ 180 kDa. HPLC fractionation to produce these three peaks at various timed intervals after injection of 125I-rt-PA showed each to have a similar initial rate half life in the rat circulation of 4-5 min. The function of these complexes as yet is unclear but since a high proportion of rt-PA is associated with a high molecular weight complex with a short half life in the rat, we suggest that the formation of this complex may be a mechanism by which t-PA activity is initially regulated and finally cleared from the rat circulation.

Permeability Enhancing and Chemotactic Activities of Lower Molecular Weight Degradation Products of Human Fibrinogen

1981 ◽  
Vol 45 (01) ◽  
pp. 090-094 ◽  
Author(s):  
Katsuo Sueishi ◽  
Shigeru Nanno ◽  
Kenzo Tanaka
Keyword(s):  
Molecular Weight ◽  
Degradation Products ◽  
Electron Microscopic Observation ◽  
Chemotactic Activity ◽  
Lower Molecular Weight ◽  
Electron Microscopic ◽  
Human Fibrinogen ◽  
Rabbit Skin ◽  
Molecular Weights ◽  
Active Fragments

SummaryFibrinogen degradation products were investigated for leukocyte chemotactic activity and for enhancement of vascular permeability. Both activities increased progressively with plasmin digestion of fibrinogen. Active fragments were partially purified from 24 hr-plasmin digests. Molecular weights of the permeability increasing and chemotactic activity fractions were 25,000-15,000 and 25,000 respectively. Both fractions had much higher activities than the fragment X, Y, D or E. Electron microscopic observation of the small blood vessels in rabbit skin correlated increased permeability with the formation of characteristic gaps between adjoining endothelial cells and their contraction.These findings suggest that lower molecular weight degradation products of fibrinogen may be influential in contributing to granulocytic infiltration and enhanced permeability in lesions characterized by deposits of fibrin and/or fibrinogen.

Toxicity of Heparinoids, with Special Reference to the Precipitation of Fibrinogen

1964 ◽  
Vol 12 (01) ◽  
pp. 232-261 ◽  
Author(s):  
S Sasaki ◽  
T Takemoto ◽  
S Oka
Keyword(s):  
Molecular Weight ◽  
Dextran Sulfate ◽  
Anticoagulant Activity ◽  
Molecular Structures ◽  
Severe Reaction ◽  
Clinical Use ◽  
Molecular Weights ◽  
Close Relationship

SummaryTo demonstrate whether the intravascular precipitation of fibrinogen is responsible for the toxicity of heparinoid, the relation between the toxicity of heparinoid in vivo and the precipitation of fibrinogen in vitro was investigated, using dextran sulfate of various molecular weights and various heparinoids.1. There are close relationships between the molecular weight of dextran sulfate, its toxicity, and the quantity of fibrinogen precipitated.2. The close relationship between the toxicity and the precipitation of fibrinogen found for dextran sulfate holds good for other heparinoids regardless of their molecular structures.3. Histological findings suggest strongly that the pathological changes produced with dextran sulfate are caused primarily by the intravascular precipitates with occlusion of the capillaries.From these facts, it is concluded that the precipitates of fibrinogen with heparinoid may be the cause or at least the major cause of the toxicity of heparinoid.4. The most suitable molecular weight of dextran sulfate for clinical use was found to be 5,300 ~ 6,700, from the maximum value of the product (LD50 · Anticoagulant activity). This product (LD50 · Anticoagulant activity) can be employed generally to assess the comparative merits of various heparinoids.5. Clinical use of the dextran sulfate prepared on this basis gave satisfactory results. No severe reaction was observed. However, two delayed reactions, alopecia and thrombocytopenia, were observed. These two reactions seem to come from the cause other than intravascular precipitation.

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