Browsing by Author "Zhuang, Hong"

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    Exploring the Factors Contributing to the High Ultimate pH of Broiler Pectoralis Major Muscles Affected by Wooden Breast Condition
    Baldi, Giulia; Yen, Con-Ning; Daughtry, Morgan R.; Bodmer, Jocelyn; Bowker, Brian C.; Zhuang, Hong; Petracci, Massimiliano; Gerrard, David E. (2020-05-08)
    The elevated ultimate pH (pH(u)) found in wooden breast (WB) meat suggests an altered muscular energetic status in WB but also could be related to a prematurely terminated post-mortem pH decline. The aims of this study were to explore the factors contributing to the elevated pH(u) and establish whether the occurrence of WB defect alters muscle post-mortem carbohydrate metabolism and determine if the contractile apparatus reflects such changes. A total of 24 carcasses from Ross 308 male chickens were obtained from a commercial producer and harvested using commercial processing procedures. Carcasses were categorized into unaffected (NORM) and WB groups (n = 12 each), and samples were collected from cranial bone-in pectoralis major (PM) muscles at 15 min and 24 h post-mortem for the determination of pH, glycolytic metabolites, adenonucleotides, buffering capacity, phosphofructokinase (PFK) activity, and in vitro pH decline. Twenty-four additional deboned PM samples (12 NORM and 12 WB) were collected from the same processing plant to assess muscle histology and sarcomere length at four different locations throughout the PM muscle. Data show that the reduced glycolytic potential of WB muscles only partially explains the higher (P < 0.001) pH(u) of WB meat, as residual glycogen along with unaltered PFK activity suggests that neither glycogen nor a deficiency of PFK is responsible for arresting glycolysis prematurely. The dramatic reduction in ATP concentrations in the early post-mortem period suggests a defective ATP-generating pathway that might be responsible for the reduced pH decline in WB samples. Further, the addition of excess of ATPase extended post-mortem glycolysis of WB meat in an in vitro glycolytic system. WB-affected samples have longer (P < 0.001) sarcomeres compared to NORM, indicating the existence of compromised energy-generating pathways in myopathic muscles that may have had consequences on the muscle contraction and tension development, as in vivo, also during the post-mortem period. Considering the overall reduced glycolytic potential and the myodegenerative processes associated with WB condition, we speculate that the higher pH(u) of WB meat might be the outcome of a drastically impaired energy-generating pathway combined with a deficiency and/or a dysfunction of muscle ATPases, having consequences also on muscle fiber contraction degree.
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    The influence of surface properties on carbon fiber/epoxy matrix interfacial adhesion
    Zhuang, Hong (Virginia Tech, 1995)
    The mechanical performance of composite materials depends not only on the matrix and the reinforcing fiber, but also to a great extent on the fiber/matrix interfacial adhesion. The focus of this work was to study carbon fiber surface chemical and physical properties and their effects on fiber/matrix adhesion. Untreated, commercially surface treated and oxygen plasma treated PAN based carbon fibers were used for study. XPS was used to determine fiber surface chemistry. A two-liquid tensiometric method was conducted to determine fiber surface energy and its dispersion and polar components. SEM was used to examine the fiber surface topography. Commercial surface treatment increased the carbon fiber surface oxygen content and fiber surface energy primarily in the polar component. An even higher level of fiber surface oxygen functionality and polar surface energy were achieved by oxygen plasma treatment. Oxygen plasma treatment also resulted in etching and pitting of AU-4 carbon fiber surface. Carbon fibers with varying surface properties were incorporated into epoxy matrices. Single fiber fragmentation tests were carried out to evaluate the strength as well as the temperature dependence and humidity durability of interfacial adhesion. Commercially treated carbon fibers which having a higher surface oxygen content and higher surface energy clearly produced superior interfacial adhesion, relative to untreated fibers. An even greater level of adhesion was achieved with oxygen plasma treated fibers. Fiber surface roughness improved durability under elevated temperature and relative humidity conditions. The presence of sodium on the fiber surface dramatically decreased durability at high relative humidity.
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    Synthesis and Characterization of Aryl Phosphine Oxide Containing Thermoplastic Polyimides and Thermosetting Polyimides with Controlled Reactivity
    Zhuang, Hong (Virginia Tech, 1998-04-14)
    Phosphorus containing monomers, bis(3-aminophenyl)methyl phosphine oxide (m-DAMPO) and bis(3-aminophenyl)phenyl phosphine oxide (m-DAPPO), were synthesized and incorporated into a thermoplastic poly(arylene ether imide) based upon 2,2'-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride and 1,3-phenylene diamine, in order to study their influence on flame resistance and other properties. DAMPO or DAPPO were quantitatively incorporated in concentrations of 25, 50, 75 and 100 mole percent, using the "one pot" ester-acid method. The number average molecular weights of the prepared materials were controlled to 20,000g/mol by off-setting the stoichiomety and endcapping with phthalic anhydride. This strategy enabled one to distinguish the effects of the phosphine oxide incoporation from the influence of molecular weight. The resulting copolymers demonstrated a significant increase in char yield as a function of the phosphine oxide content, thus suggesting improved fire resistance. Glass transition temperatures similar to the control were determined by DSC analysis. Analysis of the mechanical behavior of the DAMPO system at room temperature showed that tensile strength and elongation at failure values were comparable to the control system, while the DAPPO containing copolymers were surprisingly brittle. The influence of the reactive endgroup on the synthesis, cure behavior and network properties of thermosetting polyetherimides was investigated. Reactive phenylacetylene, acetylene and maleimide terminated poly(ether imide) oligomers were prepared and characterized. Optimal reaction conditions were established to produce fully endcapped oligomers with imidized structures and controlled molecular weight. The phenylacetylene endcapped system was synthesized by a conventional ester-acid method. The acetylene endcapped system was prepared via modified ester-acid method and the maleimide endcapped system was fabricated utilizing an amic-acid route. It was determined that phenylethynyl endcapped polymers could be thermally cured at high temperatures (350-380°C) providing good processibility. The networks exhibited thermal stability, chemical resistance and good adhesion strength, ideal as "primary" bonding adhesives. Acetylene and maleimide endcapped systems were prepared for application as "secondary" bonding materials, meaning that they are cured at a lower temperature than that of the Tg of the primary structure. Lap shear test results indicated good adhesion to titanium when cured at 250°C -280°C. The cured materials showed high glass transition temperatures and good thermal and thermo-oxidative stability as determined by DSC, TGA and DMA. Good chemical resistance was demonstrated via solvent extraction measurements. The influence of molecular weight between crosslinks (Mc) on thermal and mechanical behavior was also investigated. Lower molecular weight oligomers exhibited lower Tg and cure temperatures, whereas the cured networks resulting from lower molecular weight oligomers afforded higher Tg and higher gel fractions, but reduced toughness.