The Cross-Linking of Polyurethane Incorporated with Starch Granules and their Rheological Properties: Influences of Starch Content and Reaction Conditions

2003 ◽  
Vol 288 (7) ◽  
pp. 569-577 ◽  
Author(s):  
Seung-Kyu Ha ◽  
Hans-Christoph Broecker
Keyword(s):  
Rheological Properties ◽  
Starch Content ◽  
Cross Linking ◽  
Starch Granules ◽  
Reaction Conditions ◽  
The Cross

scholarly journals Printable Alginate Hydrogels with Embedded Network of Halloysite Nanotubes: Effect of Polymer Cross-Linking on Rheological Properties and Microstructure

Polymers ◽  
2021 ◽  
Vol 13 (23) ◽  
pp. 4130
Author(s):  
Svetlana A. Glukhova ◽  
Vyacheslav S. Molchanov ◽  
Boris V. Lokshin ◽  
Andrei V. Rogachev ◽  
Alexey A. Tsarenko ◽  
...  
Keyword(s):  
3D Printing ◽  
Rheological Properties ◽  
Shear Thinning ◽  
Halloysite Nanotubes ◽  
Polymer Chains ◽  
Cross Linking ◽  
Saxs Data ◽  
Nanocomposite Hydrogels ◽  
Embedded Network ◽  
The Cross

Rapidly growing 3D printing of hydrogels requires network materials which combine enhanced mechanical properties and printability. One of the most promising approaches to strengthen the hydrogels consists of the incorporation of inorganic fillers. In this paper, the rheological properties important for 3D printability were studied for nanocomposite hydrogels based on a rigid network of percolating halloysite nanotubes embedded in a soft alginate network cross-linked by calcium ions. Particular attention was paid to the effect of polymer cross-linking on these properties. It was revealed that the system possessed a pronounced shear-thinning behavior accompanied by a viscosity drop of 4–5 orders of magnitude. The polymer cross-links enhanced the shear-thinning properties and accelerated the viscosity recovery at rest so that the system could regain 96% of viscosity in only 18 s. Increasing the cross-linking of the soft network also enhanced the storage modulus of the nanocomposite system by up to 2 kPa. Through SAXS data, it was shown that at cross-linking, the junction zones consisting of fragments of two laterally aligned polymer chains were formed, which should have provided additional strength to the hydrogel. At the same time, the cross-linking of the soft network only slightly affected the yield stress, which seemed to be mainly determined by the rigid percolation network of nanotubes and reached 327 Pa. These properties make the alginate/halloysite hydrogels very promising for 3D printing, in particular, for biomedical purposes taking into account the natural origin, low toxicity, and good biocompatibility of both components.

scholarly journals Tartaric Acid Cross-Linking of Starch: Effect of Reaction Conditions on the Maximum Tensile Strength of Cast Plastic Films

2015 ◽  
Vol 8 (3) ◽  
Author(s):  
Arturo José Mendoza
Keyword(s):  
Tensile Strength ◽  
Tartaric Acid ◽  
Low Cost ◽  
Thermoplastic Starch ◽  
Cross Linking ◽  
Reaction Conditions ◽  
Maximum Tensile Strength ◽  
Polycarboxylic Acids ◽  
The Cross ◽  
London Dispersion

Modification of starch by cross-linking is used in many fields, as the process improves many of the properties of starch, yet most cross-linking agents in common use tend to be toxic, expensive, or both. Polycarboxylic acids could function as nontoxic alternatives to these – some, such as tartaric acid (TA) being also of low cost. This study presents a method to cross-link thermoplastic starch films with TA, as well as the effect of this modification on the tensile strength of the material when films are prepared using different reaction conditions. An increase in strength was observed, which is believed to occur due to an increase in the London dispersion forces acting within the cross-linked starch (CLS). The greatest observed increase in the maximum tensile strength of the plastic was 6%. Monosodium tartrate was used as a catalyst for the cross-linking reaction. The maximum tensile strengths of the plastics produced were determined by using adapted binder clips, a hook (total mass 10g) and hanging masses to subject films of the plastics to progressively greater tension. Incremental weights of 10g were used, with recorded tensions at fracture of 1.2~8.9 N.

Mechanical and Structural Consequences of Associative Dynamic Cross-Linking in Acrylic Diblock Copolymers

2019 ◽  
Author(s):  
Jacob Ishibashi ◽  
Yan Fang ◽  
Julia Kalow
Keyword(s):  
Block Copolymers ◽  
Rheological Properties ◽  
Diblock Copolymers ◽  
Cross Linking ◽  
Statistical Copolymer

<p>Block copolymers are used to construct covalent adaptable networks that employ associative exchange chemistry (vitrimers). The resulting vitrimers display markedly different nanostructural, thermal and rheological properties relative to those of their statistical copolymer-derived counterparts. This study demonstrates that prepolymer sequence is a versatile strategy to modify the properties of vitrimers.</p>

Ketones from Nickel-Catalyzed Decarboxylative, Non-Symmetric Cross-Electrophile Coupling of Carboxylic Acid Esters

2019 ◽  
Author(s):  
Jiang Wang ◽  
Brian P. Cary ◽  
Peyton Beyer ◽  
Samuel H. Gellman ◽  
Daniel Weix
Keyword(s):  
Carboxylic Acid ◽  
Solid Support ◽  
Reaction Conditions ◽  
Decarboxylative Coupling ◽  
New Strategy ◽  
The Cross ◽  
Acyl Donors ◽  
Acid Esters

A new strategy for the synthesis of ketones is presented based upon the decarboxylative coupling of N-hydroxyphthalimide (NHP) esters with S-2-pyridyl thioesters. The reactions are selective for the cross-coupled product because NHP esters act as radical donors and the thioesters act as acyl donors. The reaction conditions are general and mild, with over 40 examples presented, including larger fragments and the 20-mer peptide Exendin(9-39) on solid support.

High-Pressure Homogenization Alters Physicochemical Properties and In Vitro Digestibility of Chinese Yam (Dioscorea Opposita Thunb.) Starch

2018 ◽  
Vol 18 (1) ◽  
pp. 10-15
Author(s):  
Wang Yi-Wei ◽  
He Yong-Zhao ◽  
An Feng-Ping ◽  
Huang Qun ◽  
Zeng Feng ◽  
...  
Keyword(s):  
High Pressure ◽  
Physicochemical Properties ◽  
Starch Content ◽  
In Vitro Digestibility ◽  
High Pressure Homogenization ◽  
Starch Granules ◽  
Cross Polarization ◽  
Chinese Yam ◽  
Crystal Type

In this study, Chinese yam starch-water suspension (8%) were subjected to high-pressure homogenization (HPH) at 100 MPa for increasing cycle numbers, and its effect of on the physicochemical properties of the starch was investigated. Results of the polarizing microscope observations showed that the starch granules were disrupted (i.e. greater breakdown value) after HPH treatment, followed by a decrease in cross polarization. After three HPH cycles, the crystallinity of starch decreased, while the crystal type remained unaltered. Meanwhile, the contents of rapidly digestible starch and slowly digestible starch were increased. On the contrary, resistant starch content was decreased. Our results indicate that HPH treatment resulted in reduction of starch crystallinity and increase of starch digestibility.

scholarly journals Investigation of the functional network modifier loading on the stoichiometric ratio of epoxy resins and their dielectric properties

2021 ◽  
Author(s):  
Istebreq A. Saeedi ◽  
Sunny Chaudhary ◽  
Thomas Andritsch ◽  
Alun S. Vaughan
Keyword(s):  
Glass Transition ◽  
Dielectric Properties ◽  
Electrical Properties ◽  
Epoxy Resins ◽  
Functional Network ◽  
Cross Linking ◽  
Network Modifier ◽  
Epoxy Resin System ◽  
The Cross ◽  
The Impact

AbstractReactive molecular additives have often been employed to tailor the mechanical properties of epoxy resins. In addition, several studies have reported improved electrical properties in such systems, where the network architecture and included function groups have been modified through the use of so-called functional network modifier (FNM) molecules. The study reported here set out to investigate the effect of a glycidyl polyhedral oligomeric silsesquioxane (GPOSS) FNM on the cross-linking reactions, glass transition, breakdown strength and dielectric properties of an amine-cured epoxy resin system. Since many previous studies have considered POSS to act as an inorganic filler, a key aim was to consider the impact of GPOSS addition on the stoichiometry of curing. Fourier transform infrared spectroscopy revealed significant changes in the cross-linking reactions that occur if appropriate stoichiometric compensation is not made for the additional epoxide groups present on the GPOSS. These changes, in concert with the direct effect of the GPOSS itself, influence the glass transition temperature, dielectric breakdown behaviour and dielectric response of the system. Specifically, the work shows that the inclusion of GPOSS can result in beneficial changes in electrical properties, but that these gains are easily lost if consequential changes in the matrix polymer are not appropriately counteracted. Nevertheless, if the system is appropriately optimized, materials with pronounced improvements in technologically important characteristics can be designed.

scholarly journals The Effect of Surfactant-Modified Montmorillonite on the Cross-Linking Efficiency of Polysiloxanes

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2623
Author(s):  
Monika Wójcik-Bania ◽  
Jakub Matusik
Keyword(s):  
Total Pore Volume ◽  
Cross Linking ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
The Cross ◽  
Chain Lengths ◽  
First Time ◽  
Substituent Influence ◽  
Benzyl Substituent

Polymer–clay mineral composites are an important class of materials with various applications in the industry. Despite interesting properties of polysiloxanes, such matrices were rarely used in combination with clay minerals. Thus, for the first time, a systematic study was designed to investigate the cross-linking efficiency of polysiloxane networks in the presence of 2 wt % of organo-montmorillonite. Montmorillonite (Mt) was intercalated with six quaternary ammonium salts of the cation structure [(CH3)2R’NR]+, where R = C12, C14, C16, and R’ = methyl or benzyl substituent. The intercalation efficiency was examined by X-ray diffraction, CHN elemental analysis, and Fourier transform infrared (FTIR) spectroscopy. Textural studies have shown that the application of freezing in liquid nitrogen and freeze-drying after the intercalation increases the specific surface area and the total pore volume of organo-Mt. The polymer matrix was a poly(methylhydrosiloxane) cross-linked with two linear vinylsiloxanes of different siloxane chain lengths between end functional groups. X-ray diffraction and transmission electron microscopy studies have shown that the increase in d-spacing of organo-Mt and the benzyl substituent influence the degree of nanofillers’ exfoliation in the nanocomposites. The increase in the degree of organo-Mt exfoliation reduces the efficiency of hydrosilylation reaction monitored by FTIR. This was due to physical hindrance induced by exfoliated Mt particles.

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