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Papers by Christof Brändli

Encyclopedia of Materials: Science and Technology, 2001

International Journal of Adhesion and Adhesives, 2013

Abstract This study deals with the key raw material of many latent reactive polyurethane adhesive... more Abstract This study deals with the key raw material of many latent reactive polyurethane adhesives and describes the reaction of a crystalline isocyanate compound, toluenediisocyanate-uretdione (TDI-U), with a polyol matrix, e.g. polycaprolactone (PCL). Mixtures of these compounds (PCL:TDI-U with molar ratio 2:1) were investigated under isothermal and dynamic conditions with rheology, differential scanning calorimetry (DSC) and infrared spectroscopy (IR). Isothermal measurements at 80 °C showed that the solvation of TDI-U is followed after 16 min by the polyurethane formation. Isotherm storages at 40 and 60 °C and the DSC analysis according to Kissinger [1] yield in an activation energy E a of the reaction of the free NCO-groups of the TDI-U with the OH-groups of the PCL of about 85 kJ/mol. The formed polyurethane contains uretdione rings, which are opened at temperatures higher than 150 °C. The solvation process of the TDI-U seems to be an important parameter in order to control and analyse latent reactive systems and has to be investigated in further studies.

Polymers

Recycling adhesively bonded polymers is inconvenient due to its expensive separation and removal ... more Recycling adhesively bonded polymers is inconvenient due to its expensive separation and removal of adhesive residues. To tackle this problem, adhesive technologies are needed allowing debonding on demand and which do not contaminate the surface of the substrate. Direct bonding enabled by oxygen plasma treatment has already achieved substantial adhesion between flat substrates. However, debonding takes place by water, thus limiting the applications of this technology to water-free environments. The work presented in the following shows that this drawback can be overcome by grafting acrylic acid and adding copper(II) ions on the surface of polystyrene. In this process, the number of functional groups on the surface was significantly increased without increasing the surface roughness. The bonding strength between the substrates could be increased, and the process temperature could be lowered. Nevertheless, the samples could be debonded by exposure to EDTA solution under ultrasound. He...

adhäsion KLEBEN & DICHTEN

Schmelzklebstoffe gelten in der Klebstoffbranche als die problemlosen Alleskönner, wenn es um ein... more Schmelzklebstoffe gelten in der Klebstoffbranche als die problemlosen Alleskönner, wenn es um einfache, schnelle und nicht hochbelastete Verklebungen geht. Forscher arbeiten daran, die Kohäsion und Wärmebeständigkeit der Klebstoffe zu erhöhen und damit neue Anwendungen zu ermöglichen

Der Begriff «Polymer Engineering» bezeichnet die Anwendung der Polymerwissenschaft auf praktische... more Der Begriff «Polymer Engineering» bezeichnet die Anwendung der Polymerwissenschaft auf praktische Probleme im Zusammenhang mit Eigenschaften und die Verwendung von Polymermaterialien in anspruchsvollen Umgebungen. Er soll eine ganzheitliche Betrachtungsweise implizieren, von der Synthese, Verarbeitung und Oberflächenbehandlung über Konstruktion, Werkzeugtechnik und Fertigung bis zur Wiederverwertung und Entsorgung

GIT laboratory journal, 2001

Solution-based methods are one important technique for the synthesis of new inorganic materials. ... more Solution-based methods are one important technique for the synthesis of new inorganic materials. In order to achieve a reasonable throughput in synthesis applications, the use of an automated synthesis workstation is mandatory.

Die Möglichkeiten und Grenzen der im 3D-Druck-Verfahren hergestellten Spritzgussformen wurden an ... more Die Möglichkeiten und Grenzen der im 3D-Druck-Verfahren hergestellten Spritzgussformen wurden an drei Bauteilen ausgelotet. Dabei zeigte sich, dass es zwar schwierig, aber grundsätzlich möglich ist, qualitativ hochwertige Teile und filigrane Strukturen herzustellen. Voraussetzung ist, dass das Verfahren, die verwendeten Werkstoffe und Druckparameter sauber evaluiert, getestet und die Spritzgussformen spezifisch für den 3D-Druck konstruiert werden

Journal of Applied Polymer Science, 2021

Smooth polystyrene (PS) and polyamide 12 (PA 12) surfaces were produced via an injection molding ... more Smooth polystyrene (PS) and polyamide 12 (PA 12) surfaces were produced via an injection molding process followed by a smoothing process and subsequently treated with O-2 plasma to increase the number of polar groups capable of hydrogen bond formation on the surface. The presence of related groups was evident from X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The sample topographies were investigated by atomic force microscopy (AFM). The plasma treatment allowed the joining of the substrates without adhesive by pressing the substrates together below or around the glass transition temperature. Notably, not only substrates of the same polymer but also PS and PA 12, which are incompatible, were joined with this method. The adhesion between the substrates was determined using a LUMifrac apparatus. The adhesion strength increased with increasing bonding temperature and when both substrates were plasma-treated, reaching adhesive strengths up to 5.5 +/- 1.7 MPa. Remarkably, the joint substrates could be rapidly de-bonded on demand simply by treatment with water, and the separated substrates could be re-bonded by renewed plasma treatment.ISSN:1097-4628ISSN:0021-899

ADHESION ADHESIVES&SEALANTS, 2010

The new structural adhesives described in this article, which are used for bonding vehicle body s... more The new structural adhesives described in this article, which are used for bonding vehicle body shells, demonstrate that it is possible to improve even tried-and-tested, apparently indispensable products. In this case the development activities focused on increasing the adhesives' temperature stability and adhesion to metal surfaces.

Additive Manufacturing, 2019

Fused Filament Fabrication (FFF) is a popular additive manufacturing technique where molten polym... more Fused Filament Fabrication (FFF) is a popular additive manufacturing technique where molten polymer filament is applied in a raster pattern, layer by layer, to obtain the work piece. A necessary consequence of this method is a pronounced mechanical anisotropy of the product; the interface between the filaments is weaker compared to the filament itself. The strength of this interface is governed by the reptation theory which postulates a more efficient interpenetration of polymeric surfaces with decreasing polymer viscosity. This relationship was utilized in this work to modify a polycarbonate-acrylonitrile butadiene styrene polymer blend to produce FFF work pieces with less mechanical anisotropy, independent of printer settings. The tensile strength ratio of the printed interface to bulk tensile strength could be increased from 41% to 95%. Though the absolute bulk tensile strength decreases slightly, this method presents an easy and effective way to address the mechanical problems inherent in the FFF-method.

European Polymer Journal, 2018

The grafting of triethoxyvinylsilane (TEVS) onto very low density polyethylene (VLDPE) via reacti... more The grafting of triethoxyvinylsilane (TEVS) onto very low density polyethylene (VLDPE) via reactive extrusion was investigated with an emphasis on the temperature and amount of initiator used for the reaction. Two different peroxides (Luperox 101 and Peroxan PK 295P) were used as single initiators for the grafting reaction with and without an additional thermal stabilizer. Infrared spectra of the resulting polymers showed that grafting efficiency was high over the analysed temperature range from 120°C to 210°C. A new and more sensitive method, based on head space gas chromatography with mass spectrometry (head space GC-MS), was used to determine optimal grafting efficiencies. Above 160°C, the grafting efficiency for both initiators was greater than 80%. In general, grafting with the more reactive peroxide (P295) yielded more highly functionalized polymers. Optimization of the grafting process reduces the amount of unreacted grafting material, minimizing levels of free volatile components and reducing energy consumption. Melt viscosities were also analysed to identify unwanted side reactions. In general, compared to polymers produced with P295, those made with Luperox 101 exhibited more rapidly increasing complex viscosity with increasing amounts of initiator. T-peel adhesion tests were used to demonstrate the use of silane-grafted VLDPE as an adhesive on metal substrates. The T-peel strengths of modified VLDPE samples were between 0.6 and 2.6 N/mm, depending on the process conditions and the choice of initiator. The T-peel strength of Peroxan PK 295P was less dependent on initiator content, resulting in a more robust system for use in reactive extrusion technologies

CHIMIA International Journal for Chemistry, 2017

Encyclopedia of Materials: Science and Technology, 2001

International Journal of Adhesion and Adhesives, 2013

Abstract This study deals with the key raw material of many latent reactive polyurethane adhesive... more Abstract This study deals with the key raw material of many latent reactive polyurethane adhesives and describes the reaction of a crystalline isocyanate compound, toluenediisocyanate-uretdione (TDI-U), with a polyol matrix, e.g. polycaprolactone (PCL). Mixtures of these compounds (PCL:TDI-U with molar ratio 2:1) were investigated under isothermal and dynamic conditions with rheology, differential scanning calorimetry (DSC) and infrared spectroscopy (IR). Isothermal measurements at 80 °C showed that the solvation of TDI-U is followed after 16 min by the polyurethane formation. Isotherm storages at 40 and 60 °C and the DSC analysis according to Kissinger [1] yield in an activation energy E a of the reaction of the free NCO-groups of the TDI-U with the OH-groups of the PCL of about 85 kJ/mol. The formed polyurethane contains uretdione rings, which are opened at temperatures higher than 150 °C. The solvation process of the TDI-U seems to be an important parameter in order to control and analyse latent reactive systems and has to be investigated in further studies.

Polymers

Recycling adhesively bonded polymers is inconvenient due to its expensive separation and removal ... more Recycling adhesively bonded polymers is inconvenient due to its expensive separation and removal of adhesive residues. To tackle this problem, adhesive technologies are needed allowing debonding on demand and which do not contaminate the surface of the substrate. Direct bonding enabled by oxygen plasma treatment has already achieved substantial adhesion between flat substrates. However, debonding takes place by water, thus limiting the applications of this technology to water-free environments. The work presented in the following shows that this drawback can be overcome by grafting acrylic acid and adding copper(II) ions on the surface of polystyrene. In this process, the number of functional groups on the surface was significantly increased without increasing the surface roughness. The bonding strength between the substrates could be increased, and the process temperature could be lowered. Nevertheless, the samples could be debonded by exposure to EDTA solution under ultrasound. He...

adhäsion KLEBEN & DICHTEN

Schmelzklebstoffe gelten in der Klebstoffbranche als die problemlosen Alleskönner, wenn es um ein... more Schmelzklebstoffe gelten in der Klebstoffbranche als die problemlosen Alleskönner, wenn es um einfache, schnelle und nicht hochbelastete Verklebungen geht. Forscher arbeiten daran, die Kohäsion und Wärmebeständigkeit der Klebstoffe zu erhöhen und damit neue Anwendungen zu ermöglichen

Der Begriff «Polymer Engineering» bezeichnet die Anwendung der Polymerwissenschaft auf praktische... more Der Begriff «Polymer Engineering» bezeichnet die Anwendung der Polymerwissenschaft auf praktische Probleme im Zusammenhang mit Eigenschaften und die Verwendung von Polymermaterialien in anspruchsvollen Umgebungen. Er soll eine ganzheitliche Betrachtungsweise implizieren, von der Synthese, Verarbeitung und Oberflächenbehandlung über Konstruktion, Werkzeugtechnik und Fertigung bis zur Wiederverwertung und Entsorgung

GIT laboratory journal, 2001

Solution-based methods are one important technique for the synthesis of new inorganic materials. ... more Solution-based methods are one important technique for the synthesis of new inorganic materials. In order to achieve a reasonable throughput in synthesis applications, the use of an automated synthesis workstation is mandatory.

Die Möglichkeiten und Grenzen der im 3D-Druck-Verfahren hergestellten Spritzgussformen wurden an ... more Die Möglichkeiten und Grenzen der im 3D-Druck-Verfahren hergestellten Spritzgussformen wurden an drei Bauteilen ausgelotet. Dabei zeigte sich, dass es zwar schwierig, aber grundsätzlich möglich ist, qualitativ hochwertige Teile und filigrane Strukturen herzustellen. Voraussetzung ist, dass das Verfahren, die verwendeten Werkstoffe und Druckparameter sauber evaluiert, getestet und die Spritzgussformen spezifisch für den 3D-Druck konstruiert werden

Journal of Applied Polymer Science, 2021

Smooth polystyrene (PS) and polyamide 12 (PA 12) surfaces were produced via an injection molding ... more Smooth polystyrene (PS) and polyamide 12 (PA 12) surfaces were produced via an injection molding process followed by a smoothing process and subsequently treated with O-2 plasma to increase the number of polar groups capable of hydrogen bond formation on the surface. The presence of related groups was evident from X-ray photoelectron spectroscopy (XPS) and contact angle measurements. The sample topographies were investigated by atomic force microscopy (AFM). The plasma treatment allowed the joining of the substrates without adhesive by pressing the substrates together below or around the glass transition temperature. Notably, not only substrates of the same polymer but also PS and PA 12, which are incompatible, were joined with this method. The adhesion between the substrates was determined using a LUMifrac apparatus. The adhesion strength increased with increasing bonding temperature and when both substrates were plasma-treated, reaching adhesive strengths up to 5.5 +/- 1.7 MPa. Remarkably, the joint substrates could be rapidly de-bonded on demand simply by treatment with water, and the separated substrates could be re-bonded by renewed plasma treatment.ISSN:1097-4628ISSN:0021-899

ADHESION ADHESIVES&SEALANTS, 2010

The new structural adhesives described in this article, which are used for bonding vehicle body s... more The new structural adhesives described in this article, which are used for bonding vehicle body shells, demonstrate that it is possible to improve even tried-and-tested, apparently indispensable products. In this case the development activities focused on increasing the adhesives' temperature stability and adhesion to metal surfaces.

Additive Manufacturing, 2019

Fused Filament Fabrication (FFF) is a popular additive manufacturing technique where molten polym... more Fused Filament Fabrication (FFF) is a popular additive manufacturing technique where molten polymer filament is applied in a raster pattern, layer by layer, to obtain the work piece. A necessary consequence of this method is a pronounced mechanical anisotropy of the product; the interface between the filaments is weaker compared to the filament itself. The strength of this interface is governed by the reptation theory which postulates a more efficient interpenetration of polymeric surfaces with decreasing polymer viscosity. This relationship was utilized in this work to modify a polycarbonate-acrylonitrile butadiene styrene polymer blend to produce FFF work pieces with less mechanical anisotropy, independent of printer settings. The tensile strength ratio of the printed interface to bulk tensile strength could be increased from 41% to 95%. Though the absolute bulk tensile strength decreases slightly, this method presents an easy and effective way to address the mechanical problems inherent in the FFF-method.

European Polymer Journal, 2018

The grafting of triethoxyvinylsilane (TEVS) onto very low density polyethylene (VLDPE) via reacti... more The grafting of triethoxyvinylsilane (TEVS) onto very low density polyethylene (VLDPE) via reactive extrusion was investigated with an emphasis on the temperature and amount of initiator used for the reaction. Two different peroxides (Luperox 101 and Peroxan PK 295P) were used as single initiators for the grafting reaction with and without an additional thermal stabilizer. Infrared spectra of the resulting polymers showed that grafting efficiency was high over the analysed temperature range from 120°C to 210°C. A new and more sensitive method, based on head space gas chromatography with mass spectrometry (head space GC-MS), was used to determine optimal grafting efficiencies. Above 160°C, the grafting efficiency for both initiators was greater than 80%. In general, grafting with the more reactive peroxide (P295) yielded more highly functionalized polymers. Optimization of the grafting process reduces the amount of unreacted grafting material, minimizing levels of free volatile components and reducing energy consumption. Melt viscosities were also analysed to identify unwanted side reactions. In general, compared to polymers produced with P295, those made with Luperox 101 exhibited more rapidly increasing complex viscosity with increasing amounts of initiator. T-peel adhesion tests were used to demonstrate the use of silane-grafted VLDPE as an adhesive on metal substrates. The T-peel strengths of modified VLDPE samples were between 0.6 and 2.6 N/mm, depending on the process conditions and the choice of initiator. The T-peel strength of Peroxan PK 295P was less dependent on initiator content, resulting in a more robust system for use in reactive extrusion technologies

CHIMIA International Journal for Chemistry, 2017