Search results for "Oxygen permeability"
showing 10 items of 16 documents
Determination of the glass transition temperature of poly(cyclohexyl acrylate) from oxygen permeability measurements
1993
Abstract The glass transition temperature ( T g ) of poly(cyclohexyl acrylate) (PCA) has been obtained from measurements of the oxygen permeability ( P = 0.60 barrers, T g = 23.5 ± 2.0°C) using a potentiostatic electrochemical sensor, and from the oxygen diffusion coefficient ( D = 0.12 × 10 −8 cm 2 s −1 , T g = 24.0 ± 1.8°C) by the time-lag method. A T g of 25 ± 1°C was found by differential scanning calorimetry and a T g of 25.0 ± 3.5°C was obtained from the specific volume by dilatometry. The fractional free volume ( v f ) at T g is 0.020 ± 0.002, which is slightly below (∼ 20%) most glassy polymers. A linear correlation has been observed between ln D and the reciprocal of v f , which su…
New method to determine the true transmissibilities and permeabilities of oxygen in hydrogel membranes
1999
In the present paper, an electrochemical method to obtain the true transmissibilities and permeabilities of hydrogels to oxygen is proposed. The method involves the measurement of the electric current arising from the flow of oxygen through a potentiostat cell integrated by a top water layer, the hydrogel membrane, and a thin water layer between the membrane and the cathode, where the oxygen is reduced. Varying the thickness of the top water layer, the true permeation characteristics of the hydrogels are obtained. A parallel study was carried out in which the transmissibilities and permeation coefficients were obtained from the variation of the steady state current with the thickness of the…
True and Apparent Oxygen Permeabilities of Contact Lenses
1992
We studied the passage of oxygen through some commercially available contact lenses. Oxygen diffusion coefficients were determined by the time-lag method and a 201T Redher permeometer was used to measure the oxygen permeability and transmissibility by the polarographic method. The measurements were carried out at room temperature with 0.09% sodium chloride physiologic solution. The following types of lenses were tested: (1) 12 lenses of cellulose acetate butyrate (CAB) of a mean thickness of 0.194 mm (observed Dk approximately 6.3 barrers) (1 barrier is equivalent to 10(-11) cm3 of O2 (STP).cm2/cm3.s.mm Hg). (2) 13 lenses of a cross-linked polyhydroxyethyl methacrylate (2-HEMA), manufacture…
Carboxymethylation of alkali extracted xylan for preparation of bio-based packaging films
2012
This study describes the synthesis of carboxymethylxylan (CMX) and investigates its suitability as a film for packaging applications. High-purity polymeric xylan was extracted from commercial bleached birch kraft pulp and converted to CMX with three different degrees of substitution (DSs). The water vapor sorption, mechanical, and barrier properties of the films prepared from CMX were tested. Increasing DS of CMX films resulted in an increase in elongation at break and a decrease in tensile strength and Young's modulus. The DS also affected the barrier properties of the films. CMX films with higher DS showed improved (reduced) oxygen permeability (OP), and the water vapor permeability (WVP)…
Comparison of cellulose nanocrystals obtained by sulfuric acid hydrolysis and ammonium persulfate, to be used as coating on flexible food-packaging m…
2016
Cellulose nanocrystals (CNCs), extracted from trees, plants, or similar cellulose-containing materials, can be used in combination with other materials to improve their performance or introduce new applications. The main purpose of this study was to compare and understand the potentialities, as coatings for Poly(ethylene terephthalate) films, of CNCs obtained starting from the same cotton linters by two different processes: sulfuric acid hydrolysis and a less common treatment with ammonium persulfate (APS), able to provide also a cellulose oxidation. The results showed that CNCs produced through the APS treatment showed higher charge densities, due to the carboxylic groups formed during the…
Surface, mechanical and barrier properties of bio-based composite films based on chitosan and whey protein
2014
Mono-component and composite bilayer and blend films composed of chitosan and whey protein were made. Colour, microstructure, water contact angles, swelling, water vapour sorption, barrier properties (oxygen, water vapour), water vapour diffusion coefficients and mechanical properties were determined. The influence of water vapour on barrier properties was studied in relation to the surface and structural properties. Mono-component and bilayer films were transparent with a homogeneous surface. Contrarily, blend films were translucent. Bilayer films had significantly lower water vapour permeability in comparison to mono-component and blend films. In all bilayer films, the air side (chitosan)…
Oxygen permeability of hydrogel contact lenses with organosilicon moieties
2002
Oxygen transport through two extended wear (day and night) hydrogel contact lenses that contain organosilicon moieties (balafilcon A and lotrafilcon A) was studied in the hydrate (hydrogel) and dry (xerogel) states. The water uptake increased the oxygen permeability [(Dk)app] and transmissibility [Dk/L(av)] coefficients of the dry materials by about 70%. The (Dk)app for the hydrated lenses was determined following the so-called stack procedure. The values obtained were 107 +/- 4 barrer for balafilcon A and 141 +/- 5 barrer for lotrafilcon A, about 5-10 times larger than those previously reported for conventional (without organosilicon moieties) extended wear hydrogels contact lenses. The Dk…
Protection of active aroma compound against moisture and oxygen by encapsulation in biopolymeric emulsion-based edible films.
2008
International audience; Edible films made of ι-carrageenans display interesting advantages: good mechanical properties, stabilization of emulsions, and reduction of oxygen transfers. Moreover, the addition of lipids to ι-carrageenan-based films to form emulsified films decreases the transfer of water vapor and can be considered to encapsulate active molecules as flavors. The aim of this study was to better understand the influence of the composition and the structure of the carrageenan-based film matrices on its barrier properties and thus on its capacity to encapsulate and to protect active substances encapsulated. Granulometry, differential scanning calorimetry, and Fourier transform infr…
Determination of the oxygen transmissibility and permeability of hydrogel contact lenses
1999
To test the validity of the method of stacked hydrogel contact lenses to obtain the oxygen permeability and transmissibility coefficients of the lenses, the coefficients of one low hydration (38% water) and two high hydration (55 and 58% water) hydrogel contact lenses stacked one to five on an oxygen electrode were deter- mined. From the oxygen diffusion through the lenses, the current intensity in the stationary state was determined, and from this the "instrument" the oxygen transmis- sibility was obtained. The permeability coefficients of the lenses, corrected for edge effects, were obtained from the slope of the plot of the reciprocal of the transmissibility coefficients versus the lens …
Influence of high power ultrasound on physical-chemical properties of polypropylene films aimed for food packaging: barrier and contact angle features
2017
Investigation was focused on the impact of high power ultrasound (HPUS), also called thermosonication, on the oxygen permeation properties (permeability, solubility and diffusion coefficients) of barrier films aimed for food packaging. For this purpose, biaxially oriented polypropylene (BOPP) coated with acrylic/polyvinylidene chloride (BOPPAcPVDC) and biaxially oriented coextruded polypropylene (BOPPcoex) were used. The physical–chemical profile of the samples was determined using goniometry. There is a significant impact only of extreme HPUS conditions (the longest time and the highest amplitude) on the permeability, solubility and diffusion coefficients of oxygen through the BOPP films. …