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Physical Properties of Poly(alkylene oxide)s
Published in F. E. Bailey, Joseph V. Koleske, Alkylene Oxides and Their Polymers, 2020
F. E. Bailey, Joseph V. Koleske
The temperature at which an amorphous polymer or the amorphous portion of a partially crystalline polymer is transformed from a glassy state to a rubbery state is termed the glass transition temperature and is denoted by Tg. At this temperature, the modulus of a polymer undergoes marked changes of about 3 to 5 orders of magnitude, and the mechanical loss, viscous component of the complex shear modulus, dielectric loss, etc. have maxima. Tg can be determined by a variety of techniques, including mechanical, dielectric, volumetric, andcalorimetric. Tg is dependent on frequency of measurement (i.e., it is a second-order relaxation phenomenon), molecular weight, rate of heating, and other factors such as crystallinity. Because of such dependencies, various values of T. canbe found in the literature for the same polymer. Table 5 is a tabulation of Tg values for the poly(alkylene oxide)s discussed in this book. Lai and Trick (255) have also presented values for other 1,2-olefin epoxides and sulfides.
Hybrid Natural Fibers Reinforced Polymer Composite: Thermal Analysis
Published in Sajith Thottathil, Sabu Thomas, Nandakumar Kalarikkal, Didier Rouxel, Advanced Polymeric Materials for Sustainability and Innovations, 2018
The damping or Tan δ of the polymer materials is the ratio of loss modulus and storage modulus. It is related to the degree of molecular mobility in polymer material.26 Temperature corresponding to the Tan δ peak represents the glass transition temperature of the composites. The glass transition temperature is the temperature range where the state of polymer materials changes from glassy (hard, rigid) to rubbery (flexible, yielding). The effect of damping parameter on epoxy and hybrid composites as a function of temperature is shown in Figure 7.3. The maximum value of Tan δ (0.617) for epoxy shows better damping properties as compared to all the other composites. The hybrid composite J50S50 shows lower value (0.278) of Tan δ which shows good load bearing capacity due to strong adhesion between fibers and matrix. The value of Tg obtained from the curve for epoxy and composites are given in Table 7.3.
Second and Third Level Packaging Considerations for the use of Electronic Hardware at Elevated Temperatures
Published in F. Patrick McCluskey, Richard Grzybowski, Thomas Podlesak, High Temperature Electronics, 2018
F. Patrick McCluskey, Richard Grzybowski, Thomas Podlesak
The polymer portion of the adhesive can come in two forms: thermoplastic and thermosetting. A schematic illustration of these two types of polymers is shown in Figure 6.7. The thermoplastic polymer is a linear chain of linked mers (nominally, hydrogen-carbon bonds). After curing, the thermoplastic polymer becomes more rigid, but remains flexible. As the temperature is increased, the polymer essentially becomes molten. This allows for easy repair of a bonded thermoplastic joint. The thermosetting material is similar to the thermoplastic, but the chains of mers are cross-linked in three dimensions during the curing stage. The number of cross-links determines the glass transition temperature (Tg) of the polymer. In general, the more cross-links, the higher the glass transition temperature. A curing agent (e.g., a hardener) is added to a thermoplastic material to cause the cross-linking reaction. Curing can be performed using UV light, heat, or catalysts. Thermosetting materials are harder than thermoplastic, but can be processed and cured below Tg and do not become “molten” above Tg. The curing operation is not reversible, making repair difficult. Examples of thermosetting materials include epoxies and acrylics. ECAs are typically made using either thermosetting or thermoplastic polymers, or a combination of the two.
Physical and chemical properties of powder produced from spray drying of inulin component extracted from Jerusalem artichoke tuber powder
Published in Drying Technology, 2019
Raveeporn Jirayucharoensak, Krittiya Khuenpet, Weerachet Jittanit, Sarote Sirisansaneeyakul
The inulin component extracted from JAT powder had concentration of about 2 °Brix after separating the sediment by basket centrifugation. Then, the extract solutions were evaporated to the concentrations of 10, 20 and 30°Brix and spray-dried by controlling the inlet/outlet drying air temperatures at 150/90 °C. The powder recovery percentage, color, moisture content, and water activity values of inulin powders obtained from all spray drying runs are presented in Table 2. It appeared that the powder recovery percentage was significantly greater when increasing the feed concentration. This result should be related to the moisture content of powder. The higher concentration implied the less moisture proportion in the feed solution. As a result, when the solutions were spray-dried using the identical drying air temperature, the solution with greater concentration would provide the lower moisture content of powder product. The inulin powder containing lesser moisture content would have higher glass transition temperature leading to more stable and less rubbery characteristic of powder samples.[21,42] Subsequently, less solids were stuck on the surface of drying chamber, cyclone, and piping system leading to higher powder recovery. Amrutha et al.[56] stated that the glass transition temperature is the temperature at which the amorphous phase of the polymer is transformed to a phase between rubbery and glassy states. The low glass transition temperature leaded to the stickiness and hygroscopicity of spray-dried powder and subsequently causing low powder yield and operational problems in spray drying. Zimeri and Kokini[42] investigated the glass transition temperature of powdered pre-solubilized inulin and native inulin powder (Raftiline HP, > 99.5% purity, DP ≥25) and found that the glass transition temperatures of both inulin powder samples decreased with increasing moisture contents due to the plasticizing effect of water. At the moisture content of about 15% d.b the glass transition temperature was 40 °C while it was approximately 62 °C when the moisture content was 10% d.b. A similar trend was also found by Ronkart et al.[21]. They revealed that the glass transition temperature of inulin powder (Warcoing, Belgium, DP =10) at the moisture content of around 5% wet basis (w.b.) was 70 °C while they were approximately 40 and 20 °C when the moisture contents were 9 and 11% w.b., respectively. They also pointed out that the agglomeration, caking, and textural instability of the inulin powder can occur when the temperature of inulin powder is above its glass transition temperature. In the present study, the higher concentration than 30°Brix could not be applied since it caused the injection problem of the two-fluid nozzle of this spray dryer.