Polyurethan VC, a Virtually Crosslinked Elastomer

1962 ◽  
Vol 35 (3) ◽  
pp. 742-752 ◽  
Author(s):  
C. S. Schollenberger ◽  
H. Scptt ◽  
G. R. Moore
Keyword(s):  
Room Temperature ◽  
Weather Conditions ◽  
Outdoor Exposure ◽  
Accelerated Weathering ◽  
High Tensile Strength ◽  
Beneficial Effects ◽  
Ultraviolet Absorbers ◽  
Weather Resistance ◽  
Induced Changes ◽  
Ozone Resistance

Abstract Many of the outstanding physical properties that characterize elastomeric Polyurethans have been realized in a soluble, thermoplastic variety, Polyurethan VC, which displays the superficial properties of a rubbery vulcanizate at room temperature and so is considered to be virtually crosslinked. High tensile strength as well as good tear, abrasion, solvent, oil, and ozone resistance characterizes this polymer. Since these properties are realized in the unvulcanized state, many useful applications of the readily processable polymer can be made, avoiding the complications which attend the use of conventional (vulcanizing) urethan elastomers. Outdoor exposure and indoor accelerated weathering studies demonstrated a deficiency in the weather resistance of the raw polymer. Weather-induced changes, believed to be due to ultraviolet-initiated autoxidation, have been estimated by noting changes in the stress-strain properties as well as the ultraviolet and infrared absorption spectra of the polymer on exposure to natural and artificial weather conditions. The beneficial effects of certain carbon blacks, conventional antioxidants, and ultraviolet absorbers on the weather resistance of the polymer have been described.

Wood-adhesive interactions in a PVAc latex

Holzforschung ◽  
2008 ◽  
Vol 62 (4) ◽  
Author(s):  
Francisco López-Suevos ◽  
Charles E. Frazier
Keyword(s):  
Vinyl Acetate ◽  
Coupling Model ◽  
Wood Adhesive ◽  
Poly Vinyl Alcohol ◽  
Accelerated Weathering ◽  
Adhesive Interaction ◽  
Adhesive Interactions ◽  
Weather Resistance ◽  
Induced Changes ◽  
Neat Films

Abstract Static rheological analysis based on time/temperature equivalence was applied to freestanding poly(vinyl acetate-co-N-methylolacrylamide) (PVAc-co-NMA) adhesive films and to wood-bonded films (composites) containing two types of crosslinking: 1) AlCl3 catalysis of NMA comonomer, and 2) the same AlCl3 catalysis plus additional crosslinking using a phenolic resol additive, PF. The glass/rubber relaxations for bulk poly(vinyl acetate), PVAc, and in some cases for the poly(vinyl alcohol) interfacial agent (PVOH) also, were evaluated by the empirical Kohlrausch-Williams-Watts (KWW) coupling model. The KWW coupling analysis revealed that accelerated weathering dramatically decreased PVAc segmental coupling in neat films; the PF additive slightly mitigated this weathering effect. In comparison to neat films, composite specimens exhibited increased PVAc coupling for all sample types, demonstrating a significant wood-adhesive interaction. In contrast to neat films, the PF additive completely negated the effects of accelerated weathering in composite specimens. Since PF prevented weathering-induced changes to the PVAc relaxation (in composites), the phenolic additive influenced the bulk adhesive and its effects were not restricted to PVOH crosslinking at the interparticle boundaries. The wood-adhesive interaction was not only detected through the PVAc relaxation but also in the PVOH glass transition. Furthermore, the PF borne weather resistance was dependent upon the presence or absence of wood, suggesting a PF/wood interaction. It is unknown if the putative PF/wood interaction is direct or possibly indirect through wood alteration of PVAc and PVOH.

scholarly journals Exogenous application of growth stimulators improves the condition of maize exposed to soil drought

2021 ◽  
Vol 43 (4) ◽  
Author(s):  
Agnieszka Ostrowska ◽  
Maciej T. Grzesiak ◽  
Tomasz Hura
Keyword(s):  
Plant Growth ◽  
Developmental Stages ◽  
Aminolevulinic Acid ◽  
Stem Elongation ◽  
Development Stage ◽  
Photochemical Activity ◽  
Soil Drought ◽  
Beneficial Effects ◽  
Induced Changes ◽  
The Impact

AbstractSoil drought is a major problem in plant cultivation. This is particularly true for thermophilic plants, such as maize, which grow in areas often affected by precipitation shortage. The problem may be alleviated using plant growth and development stimulators. Therefore, the aim of the study was to analyze the effects of 5-aminolevulinic acid (5-ALA), zearalenone (ZEN), triacontanol (TRIA) and silicon (Si) on water management and photosynthetic activity of maize under soil drought. The experiments covered three developmental stages: three leaves, stem elongation and heading. The impact of these substances applied during drought stress depended on the plant development stage. 5-ALA affected chlorophyll levels, gas exchange and photochemical activity of PSII. Similar effects were observed for ZEN, which additionally induced stem elongation and limited dehydration. Beneficial effects of TRIA were visible at the stage of three leaves and involved leaf hydration and plant growth. A silicon preparation applied at the same developmental stage triggered similar effects and additionally induced changes in chlorophyll levels. All the stimulators significantly affected transpiration intensity at the heading stage.

Exposure of Polymeric Glazing Materials Using NREL’s Ultra-Accelerated Weathering System (UAWs)

2010 ◽  
Author(s):  
Carl Bingham ◽  
Gary Jorgensen ◽  
Amy Wylie
Keyword(s):  
Light Intensity ◽  
Thermal Effects ◽  
Outdoor Exposure ◽  
Exposure Chamber ◽  
Accelerated Weathering ◽  
Intensity Level ◽  
Design And Implementation ◽  
Different Temperatures ◽  
Exposure Testing ◽  
Ultraviolet Irradiance

NREL’s Ultra-Accelerated Weathering System (UAWS) selectively reflects and concentrates natural sunlight ultraviolet irradiance below 475 nm onto exposed samples to provide accelerated weathering of materials while keeping samples within realistic temperature limits. This paper will explain the design and implementation of the UAWS which allow it to simulate the effect of years of weathering in weeks of exposure. Exposure chamber design and instrumentation will be discussed for both a prototype UAWS used to test glazing samples as well as a commercial version of UAWS. Candidate polymeric glazing materials have been subjected to accelerated exposure testing at a light intensity level of up to 50 UV suns for an equivalent outdoor exposure in Miami, FL exceeding 15 years. Samples include an impact modified acrylic, fiberglass, and polycarbonate having several thin UV-screening coatings. Concurrent exposure is carried out for identical sample sets at two different temperatures to allow thermal effects to be quantified along with resistance to UV.

scholarly journals Temperate UV-Accelerated Weathering Cycle Combined with HT-GPC Analysis and Drop Point Testing for Determining the Environmental Instability of Polyethylene Films

Polymers ◽  
2021 ◽  
Vol 13 (14) ◽  
pp. 2373
Author(s):  
Celine Moreira ◽  
Richard Lloyd ◽  
Gavin Hill ◽  
Florence Huynh ◽  
Ana Trufasila ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Outdoor Exposure ◽  
Accelerated Weathering ◽  
Polyethylene Films ◽  
Parallel Testing ◽  
Mapping Analysis ◽  
Environmental Instability ◽  
Weight Analysis ◽  
Physical Changes ◽  
Ir Spectroscopic

Polyethylene films are one of the most frequently used packaging materials in our society, due to their combination of strength and flexibility. An unintended consequence of this high use has been the ever-increasing accumulation of polyethylene films in the natural environment. Previous attempts to understand their deterioration have either focused on their durability using polymer analysis; or they have focused on changes occurring during outdoor exposure. Herein, this study combines those strategies into one, by studying the chemical and physical changes in the polyethylene structure in a laboratory using molecular weight and IR spectroscopic mapping analysis, combined with temperate UV-accelerated weathering cycles. This approach has been correlated to real-world outdoor exposure timeframes by parallel testing of the sample polyethylene films in Florida and France. The formation of polyethylene microparticles or polyethylene waxes is elucidated through comparison of drop point testing and molecular weight analysis.

scholarly journals Correlation of a Temperate UV-Weathering Cycle to Outdoor Exposure for the Determination of the Environmental Instability of Polyethylene Films Using HT-GPC Analysis

Polymers ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 591
Author(s):  
Gavin Hill ◽  
Celine Moreira ◽  
Florence Huynh ◽  
Ana Trufasila ◽  
Faith Ly ◽  
...  
Keyword(s):  
Physical Property ◽  
Gel Permeation Chromatography ◽  
Outdoor Exposure ◽  
Accelerated Weathering ◽  
Micro Particles ◽  
Exposure Site ◽  
Plastic Materials ◽  
Physico Chemical ◽  
Environmental Instability ◽  
Insight Into

Accelerated UV-weathering cycles are predominately used for evaluating the durability of plastic materials, particularly polyethylene (PE) films. The point of failure for this testing is usually the loss of a physical property, such as the loss of tensile strength over time. For plastics designed to be instable under environmental conditions, the accelerated weathering cycles are yet to be defined and their correlation to outdoor exposure has yet to be made. This study demonstrates the utility of a newly defined temperate accelerated UV-weathering cycle, recently codified in the British Standard PAS 9017:2020. In addition, the effectiveness of the laboratory weathering cycle has been correlated to real-world outdoor exposure through simultaneous testing of the same samples at a specialist outdoor exposure site in Florida. The utility of the testing methodology and the performance of the polyethylene samples was demonstrated through the use of High Temperature Gel Permeation Chromatography (HT-GPC) analysis. The data led to a detailed insight into the physico-chemical changes occurring in the PE films upon exposure to environmental stimuli. By comparison, and surprisingly, the techniques employed appear to provide an insight into the processes in which secondary micro-particles of PE are formed from macro-polyethylene samples. The temperate accelerated UV-weathering cycle over 14 days demonstrated an approximate correlation to 90 days of outdoor exposure in Florida for the PE film studied.

Hypoxia-induced changes in shivering and body temperature

1987 ◽  
Vol 62 (6) ◽  
pp. 2477-2484 ◽  
Author(s):  
H. Gautier ◽  
M. Bonora ◽  
S. A. Schultz ◽  
J. E. Remmers
Keyword(s):  
Central Nervous System ◽  
Body Temperature ◽  
Room Temperature ◽  
Co2 Concentration ◽  
Hypoxic Conditions ◽  
O2 Concentration ◽  
The Central Nervous System ◽  
Induced Changes ◽  
Maintain Body Temperature ◽  
Ambient Hypoxia

Experiments were carried out on conscious cats to evaluate the general characteristics and modes of action of hypoxia on thermoregulation during cold stress. Intact and carotid-denervated (CD) conscious cats were exposed to ambient hypoxia (low inspired O2 fraction) or CO hypoxia in prevailing laboratory (23–25 degrees C) or cold (5–8 degrees C) environments. In the cold, both groups promptly decreased shivering and body temperature when exposed to either type of hypoxia. Small increases in CO2 concentration reinstituted shivering in both groups. At the same inspired concentration of O2, CD animals decreased shivering and body temperature more than intact cats. While this difference resulted, in part, from a lower alveolar PO2 in CD cats, a difference between intact and CD cats was apparent when the two groups were compared at the same alveolar PO2. During more prolonged hypoxia (45 min), shivering returned but did not reach normoxic levels, and body temperature tended to stabilize at a hypothermic value. Exposure to various levels of hypoxia produced graded suppression of shivering, with the result that the change in body temperature varied directly with inspired O2 concentration. Hypoxia appears to act on the central nervous system to suppress shivering and sinus nerve afferents appear to counteract this direct effect of hypoxia. In intact cats, this counteraction appears to be sufficient to maintain body temperature under hypoxic conditions at room temperature but not in the cold.

Influence of Temperature and Oxygen Concentration on the Radiation Induced Oxidation of Phenylalanine

1995 ◽  
Vol 50 (9) ◽  
pp. 864-870 ◽  
Author(s):  
P. Krajnik ◽  
R. M. Quint ◽  
S. Solar ◽  
N. Getoff ◽  
G. Sontag
Keyword(s):  
Oxygen Concentration ◽  
Room Temperature ◽  
Degradation Process ◽  
Storage Conditions ◽  
Food Storage ◽  
Reaction Conditions ◽  
Influence Of Temperature ◽  
Influence Of Temperature On ◽  
Radiation Induced ◽  
Induced Changes

AbstractThe formation of tyrosine isomers by γ-radiolysis of neutral aqueous phenylalanine solutions was found to be strongly dependent on oxygen concentration and temperature. Changing the dose rate did not influence the degradation process. In the presence of 0.25 x 10-3 mol dm-3 oxygen at room temperature the yields of o-tyrosine as well as of m- and p-tyrosine drop from G(o-Tyr) = 0.5 and G(m-Tyr) = G(p-Tyr) = 0.4 at a dose of 0.3 kGy to 0.18 and 0.16 at 2.5 kGy, respectively. In solutions containing 1.25 x 10-3 mol dm-3 oxygen the initial yields remain unchanged but decrease at 2.5 kGy only to G(o-Tyr) = 0.3 and G(m-Tyr) = G(p-Tyr) = 0.20. Under the latter reaction conditions also 3,4-dihydroxyphenylalanine was found.Samples irradiated in frozen state did not show remarkable radiolysis of phenylalanine and tyrosine formation. In the range between 5 and 20°C no essential influence of temperature on the phenylalanine radiolysis and tyrosine yields was observable. The obtained results are important for methods using the tyrosine yields as markers for the detection of irradiated food. Storage conditions and irradiation temperature play an essential role on radiation induced changes of food.

scholarly journals The Effect of Ultrasound, Oxygen and Sunlight on the Stability of (−)-Epigallocatechin Gallate

Molecules ◽  
2018 ◽  
Vol 23 (9) ◽  
pp. 2394 ◽  
Author(s):  
Jiajun Zeng ◽  
Huanhua Xu ◽  
Yu Cai ◽  
Yan Xuan ◽  
Jia Liu ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
High Performance ◽  
Room Temperature ◽  
Degradation Rate ◽  
Epigallocatechin Gallate ◽  
Important Conclusion ◽  
Beneficial Effects ◽  
Periodontal Infection ◽  
The Stability ◽  
Ultrasonic Conditions

(−)-Epigallocatechin gallate (EGCG), is the main catechin found in green tea, and has several beneficial effects. This study investigated the stability of EGCG aqueous solution under different stored and ultrasonic conditions to determine whether it can be used with an ultrasonic dental scaler to treat periodontal infection. Four concentrations (0.05, 0.1, 0.15, 2 mg/mL) of EGCG aqueous solution were prepared and stored under four different conditions (A: Exposed to neither sunlight nor air, B: Exposed to sunlight, but not air, C: Not exposed to sunlight, but air, D: Exposed to sunlight and air) for two days. The degradation rate of EGCG was measured by high performance liquid chromatography (HPLC). On the other hand, an ultrasonic dental scaler was used to atomize the EGCG solution under four different conditions (a: Exposed to neither air nor sunlight, b: Not exposed to air, but sunlight, c: Not exposed to sunlight, but air, d: Exposed to air and sunlight), the degradation of EGCG was measured by HPLC. We found that the stability of EGCG was concentration-dependent in water at room temperature. Both sunlight and oxygen influenced the stability of EGCG, and oxygen had a more pronounced effect on stability of EGCG than sunlight. The most important conclusion was that the ultrasound may accelerate the degradation of EGCG due to the presence of oxygen and sunlight, but not because of the ultrasonic vibration. Thus, EGCG aqueous solution has the potential to be used through an ultrasonic dental scaler to treat periodontal infection in the future.

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