670 Industrielle und handwerkliche Fertigung
Refine
Year of publication
- 2018 (4) (remove)
Document Type
- Journal article (4)
Language
- English (4)
Is part of the Bibliography
- yes (4)
Institute
- Life Sciences (4) (remove)
Publisher
- Elsevier (3)
- American Chemical Society (1)
Impact of phenolic resin preparation on its properties and its penetration behavior in Kraft paper
(2018)
The core of decorative laminates is generally made of stacked Kraft paper sheets impregnated with a phenolic resin. As the impregnation process in industry is relatively fast, new methods need to be developed to characterize it for different paper-resin systems. Several phenolic resins were synthesized with the same Phenol:Formaldehyde ratio of 1:1.8 and characterized by Fourier Transform Infrared Spectrometry (FTIR) as well as Size-Exclusion Chromatography (SEC). In addition, their viscosities and surface tensions when diluted in methanol to 45% of solid content were measured. The capacity of each resin to penetrate a Kraft paper sheet was characterized using a new method, which measures the conductivities induced by the liquid resin crossing the paper substrate. With this method, crossing times could be measured with a good accuracy. Surprisingly, the results showed that the penetration time of the resin samples is not correlated to the viscosity values, but rather to the surface tension characteristics and the chemical characteristics of paper. Furthermore, some resins had a higher swelling effect on the fibers that delayed the crossing of the liquid through the paper.
Functionalised particles are highly requested in materials research, as they can be used as vital components in many advanced applications such as smart materials, functional coatings, drug carrier systems or adsorption materials. In this study, furan-functionalised melamine-formaldehyde (MF) particles were successfully prepared for the first time using an organic sol-gel process. Commercially available 2-Aminomethylfuran (AMF) and 2-Aminomethyl-5-methylfuran (AMMF) were used as modifying agents. In the isolated polymer particles, a melamine (M) to modifying agent ratio of M:AMF mol/mol 2.04:1 and M:AMMF ratio of mol/mol 1.25:1 was used. The obtained particles were isolated in various centrifugation and re-dispersion cycles and analysed using ATR-FT-IR, Raman and solid state 13C NMR spectroscopy, TGA, SEM and DSC measurements. Upon functionalisation the size of the MF particles increased (MF 1.59 µm, 27% CV (coefficient of variation); MF-AMF 2.56 µm, 25% CV; MF-AMMF 2.20 µm, 35% CV). DSC measurements showed that another type of exothermic residual reactivity besides condensation-based curing takes place with the furan-modified particles that is not related to the liberation of volatile compounds. The newly obtained particles are able to undergo Diels-Alder reactions with maleimide groups. The characteristic IR and Raman absorbance bands of the reaction products after the particles were reacted with 4,4′-Diphenylmethanebismaleimide reagent confirm the formation of a Diels-Alder adduct.
Soft thermoplastic polysiloxane-urea-elastomers (PSUs) were prepared for the application as a biomaterial to replace the human natural lens after cataract surgery. PSUs were synthesized from amino-terminated polydimethylsiloxanes (PDMS), 4,4′-Methylenebis(cyclohexylisocyanate) (H12MDI) and 1,3–Bis(3-aminopropyl)-1,1,3,3–tetramethyldisiloxane (APTMDS) by a two-step polyaddition route. Such a material has to be highly transparent and must exhibit a low Young’s Modulus and excellent dimensional stability. Polydimethylsiloxanes in the range of 3000–33,000 g·mol−1 were therefore prepared by ring-chain-equilibration of octamethylcyclotetrasiloxane (D4) and APTMDS in order to study the influence of the soft segment molecular weight on the mechanical properties and the transparency of the PSU-elastomers. 2,4,6,8-Tetramethyl-2,4,6,8-tetraphenylcyclotetrasiloxane (D4Me,Ph) was co-polymerized with D4 in order to adjust the refractive index of the polydimethyl-methyl-phenyl-siloxane-copolymers to a value equivalent to a young human natural lens. Very elastic PSUs with Elongation at Break values higher than 700% were prepared. PSU-elastomers, synthesized from PDMS of molecular weights up to 18,000 g·mol−1, showed transmittance values of over 90% within the visible spectrum range. The soft segment refractive index was increased through the incorporation of 14 mol % of methyl-phenyl-siloxane from 1.4011 to 1.4346 (37 °C). Young’s Moduli of PSU-elastomers were around 1 MPa and lower at PDMS molecular weights up to 15,000 g·mol−1. 10-cycle hysteresis measurements were applied to evaluate the mechanical stability of the PSUs at repeated stress. Hysteresis values at 100% strain decreased from 32 to 2% (10th cycle) with increasing PDMS molecular weight. Furthermore, hysteresis at 5% strain was only detected in PSU-elastomers with low PDMS molecular weights. Finally, preliminary results of in vitro cytotoxicity tests on a PSU-elastomer showed no toxic effects on HaCaT-cells.
Polyelectrolyte multilayer (PEM) are thin polymeric films produced by alternating adsorption of positively and negatively charged polyelectrolytes (PE) on a substrate. These films are considered drug delivery agents as well as coating material for implants, due to their antibiofouling and biologically benign properties. For these reasons the film mechanical properties as well as response to mechanical stress are important measurement parameters. Especially intriguing is the correlation of the mechanical properties of PEM on macroscopic level with the structure of PEM on molecular level, which is addressed here for the first time. This study investigates PEM from PDADMA/PSS produced by spraying technique with neutron and X-ray reflectometry. Reflectometry technique provides precise information on thickness and density (i.e., electron density or scattering length density, respectively), and, this way, allows to conclude on changes in film composition. Thus, neutron and X-ray reflectometry technique is suitable to investigate the overall and the internal transformations, which PEM films might undergo upon exposure to mechanical load. During uniaxial elongation two regimes of PEM deformation can be observed: An elastic regime at small elongations (below ca. 0.2%), which is characterized by a reversible change of film thickness, and a plastic regime with a permanent change above this limit. Both regimes have in common, that the mechanical load induces an increase of the film thickness, which is accompanied by an uptake of water from the surrounding atmosphere. The strain causes a molecular rearrangement within the PEM-structure of stratified layers, which, even in elastic regime, is permanent, although the thickness change remains reversible.