دانلود رایگان مقاله لاتین صمغ ژلان حاوی ژل مایع از سایت الزویر
عنوان فارسی مقاله:
آزمون خزش بازیابی خزش برای تعیین تنش حاصل از صمغ ژلان حاوی ژل های مایع و Na +
عنوان انگلیسی مقاله:
Creep-recovery-creep tests to determine the yield stress of fluid gels containing gellan gum and Na+
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Fluid gels are heterogeneous materials at the microstructure level which consist of dispersions with a structure based on the existence of gelled polymeric aggregates with similar properties to weak gels. They find applications in the food industry [1–3] and biomedicine such as oral drug delivery [4,5] or artificial lacrimal fluid [6], mainly as suspension agents [7,8] and conceivably as satiety agents [9]. From a rheological point of view, fluid gels must exhibit a rapid fall in viscosity with shear time in the shear rate range associated with industrial applications and also a rapid recovery of viscosity after cessation of shear in order to avoid a phase separation of dispersed particles. They can be considered as yield stress fluids, which are those that have a complex microstructure and need to exceed a minimum shear stress in order to flow at a significant shear rate. This minimum shear stress is known as the yield stress. These types of materials consist of structured fluids, such as foams, concentrated emulsions, colloidal gels, microgel suspensions or dense suspensions. Such materials can be divided into ideal yield stress fluids (those exhibiting Bingham or HerschelBulkley behaviour) and non-ideal yield stress fluids (those which also exhibit thixotropy) [10]. Furthermore, the latter are usually sensitive to thermo-mechanical history and susceptible toageing [11]. These rheological properties conform to their internal network structure and micro-scale heterogeneity [12]. In fact, a recently study has indicated that most of these materials consist of either colloidal glasses or colloidal gels [13]. Therefore, the rheological characterization of these materials has been traditionally difficult due to their structural complexity [14–16]. Several techniques have been used to determine the yield stress (flow curves, creep, oscillatory shear and stress ramp) [17] and the thixotropy (hysteresis loops, stepwise changes in shear rate or shear stress and start-up experiments) [18,19] ofthese materials. However, some of these techniques are likely to yield experimental artefacts. In this work we determine (1) the practical yield stress value of a structured fluid exhibiting very shear thinning behaviour, which is the case of fluid gels based on low-acyl gellan gum and (2) the onset of thixotropic properties. Gellan gum is an anionic polysaccharide that can be obtained through microbial fermentation from Sphingomonas elodea (ATCC 31462) [8]. In order to obtain low-acyl gellan gum fluid gels, Sworn [8] suggested that dispersion, hydration and gelation under shear must be performed, sodium being one ofthe cations which promote the formation of gels. Regarding the gelation step under shear, it can be achieved by two alternative procedures. On the one hand, the sample may be submitted to mechanical treatment for a given time once the threshold temperature for the inception of gelation is reached [19]. On the other hand, it can be performed by application of steady mechanical energy during the cooling step [20–22]. A recent study has demonstrated the ability of creep-recovery creeptests in series to determine a practical yield stress simultaneously to the onset of non-linear time-dependent rheological behaviour of a gellan gum fluid gel formulated with Ca 2+ as gel promoting cation [21]. The objective of this study was to assess the validity of the method based on creep-recovery-creep tests to obtain both the yield stress and the inception of non-linear time-dependent rheological behaviour of fluid gels, as examples of very shear thinning materials. Namely, this work checks the suitability of the aforementioned method when applied to a low acyl-gellan gum fluid gel containing sodium as gel-promoting ion.
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کلمات کلیدی:
[PDF]Development of Gellan Gum Blend Fluid Gels as Topical Formulations abstracts.aaps.org/Verify/AAPS2015/PosterSubmissions/R6047.pdf Development of Gellan Gum Blend Fluid Gels as Topical Formulations ... Stress sweeps for 1% gellan fluid gels crosslinked with 0.5% NaCl, as function of ... KELCOGEL® Gellan Gum - CP Kelco https://www.cpkelco.com/markets-served/household-products/.../kelcogel-gellan-gum/ However, with low concentrations of gellan gum, shearing the gel results in the ... are very good at suspending particulate matter since, provided the stress exerted ... Gellan gum fluid gels have a high low-shear viscosity, providing remarkable ... KELCOGEL ® Gellan Gum - CP Kelco https://www.cpkelco.com/markets-served/pharmaceuticals/.../kelcogel-gellan-gum/ Gellan gum fluid gels are solutions with a weak gel structure. They exhibit an apparent yield stress, i.e., a finite stress that must be exceeded before the system ... [PDF]Creep-recovery-creep tests to determine the yield stress of fluid gels ... iranarze.ir/wp-content/uploads/2016/10/E448.pdf Jul 18, 2016 - Creep-recovery-creep tests to determine the yield stress of fluid gels containing gellan gum and Na+. Ma Carmen García, Ma Carmen Alfaro∗, ... Food Stabilisers, Thickeners and Gelling Agents - Google Books Result https://books.google.com/books?isbn=1444360337 Alan Imeson - 2011 - Technology & Engineering Gels made with the high-acyl form of gellan gum generally show little thermal hysteresis as ... With low ionic strength gels, these two temperatures are within 3°C of each other. ... In fact, fluid gels made with gellan gum have a yield stress. [PDF]Kelcogel Book - Applied Bioscience Consultants & Distributors www.appliedbioscience.com/docs/Gellan_Book_5th_Edition.pdf final gel strength of low acyl gellan gum are also ..... Gellan gum fluid gels are solutions with a weak gel ... fluid gel formulation of KELCOGEL® gellan gum, at. Cellulose and Cellulose Derivatives in the Food Industry: ... https://books.google.com/books?isbn=352733758X Tanja Wuestenberg - 2016 - SCIENCE In fact, fluid gels including gellan gum have a yield stress that keeps particles in ... Gellan is also mixed with other gelling and non-gelling hydrocolloids to modify ...
