Glass Bonding

 

Enhancing Glass Bonding Characteristic with Silanes and Polymer Coatings

Although glasses are often valued for their chemical inertness, this property also presents challenges when attempting to form strong chemical bonds with other materials. Silanes and polymer coatings offer effective solutions by enhancing the bond between a glass and other materials in a composite.

The Challenge

The challenge of bonding glass to polymers spans across several industries, including industrial, automotive, and healthcare. In biomaterial applications, polymer carriers are often used to deliver glass or ceramic particles to specific treatment sites. However, bioactive glasses, commonly used in treatment delivery and bone regeneration, face a similar issue: the mismatch in critical surface tension and adhesion properties between the materials in the composite.¹ This mismatch is primarily driven by differences in hydrophobicity and hydrophilicity, making it difficult to create strong, stable bonds.

The key question, then, is how to improve and strengthen the bonds between glass and polymer materials to create stable composites that benefit from the properties of both material types.

The Solution

Fortunately, there are several approaches to improving the bonding characteristics of glass. One such solution is the use of silane or polymer materials as adhesive treatments. These materials help bypass the challenges of forming direct chemical bonds between the surface oxide groups on the glass and the substrate of interest.

Silanes

Silanes are particularly effective in improving the bonding between glass and other materials due to their ability to form highly stable siloxane bonds. These strong covalent bonds enhance the compatibility between glass and various organic or inorganic surfaces, creating a stronger interface than unmodified glass. Silanes are an excellent choice for composites, retaining the properties of glass while significantly improving surface chemistry and wettability.

One challenge in forming glass-bonded materials is the introduction of a new surface type, which can create potential regions of weakness and shear. Silanes act as effective coupling agents by forming strong covalent bonds with both the glass and the substrate, reducing these weak points and enhancing the overall stability and durability of the material.²

While physical abrasion and etching with hydrofluoric acid can improve adhesion by roughening the surface, chemical modification using silanes is often preferable. Chemical bonds offer superior grafting properties compared to physical methods, resulting in stronger, more durable connections between glass and other substrates.

Polymers

Polymer materials are widely used for bonding to glass due to their flexibility, which is highly advantageous in adhesive applications. While silicone-based materials can bond to glass, they are generally not as strong as many polymer adhesive options.

One such polymer adhesive, polyurethane, is a popular choice for bonding glass in various industries. This popularity is due to its flexibility, which helps absorb and mitigate vibrations induced by movement, enhancing the durability and integrity of the bonded structure. Similarly, acrylic adhesives are the ideal choice for oily or corrosive environments or for use in high-temperature applications. Epoxy adhesives also offer similar benefits, with excellent chemical and electrical resistance.

While many polymers show good adhesion to glass surfaces, their bonding interactions tend to be weaker than the covalent bonds formed with silanes, relying instead on intermolecular forces.³

Polymer adhesion is sufficient for many applications, especially where motion or substrate deformation is likely, as flexibility in the bonding is beneficial. However, for applications that demand the highest levels of adhesion, combining silane treatment with polymer bonding provides a superior solution. This approach significantly enhances bond strength, making it ideal for situations requiring both flexibility and durability.

MO SCI Solutions

MO SCI has a long history of developing custom glass solutions for even the most challenging applications. We can help you find innovative and effective ways to overcome the challenges of glass bonding and adherence to create devices that not only have the properties for peak application performance but are also stable and resistant to environmental degradation.

Contact us today to discuss your application.

Rebecca Straw

References and Further Reading

1. Brauer, D. S. (2015). Bioactive Glasses — Structure and Properties Angewandte. Angewandte Chemie – International Edition, 54, 4160–4181. https://doi.org/10.1002/anie.201405310

2. Yavuz, T., & Eraslan, O. (2016). The effect of silane applied to glass ceramics on surface structure and bonding strength at different temperatures. Journal of Advced Prosthodontics, 75–84. https://doi.org/10.4047%2Fjap.2016.8.2.75

3. Park, H., & Lee, S. H. (2021). Review on Interfacial Bonding Mechanism of Functional Polymer Coating on Glass in Atomistic Modeling Perspective. Polymers, 13, 2244. https://doi.org/10.3390/polym13142244

A low-cost Strip Cutting Method

 Cutting strips is repetitive, but requires accuracy. This can be achieved with expensive tools that do the job very well. It can also be done with only a few tools – most of which you already have.

This photo shows some of them.

The adjustable try square is really useful, as once it is set, you can be sure all the distances will be the same. The distance should be the width you require plus half the width of your cutter head – usually 2mm.

You put the nails into the bench or a board along a straight edge as measured by the try square. Check them both after hammering them in.

Place the glass edge along the edge of the board/bench. Use the normal cutting square to place against the nails. Then draw the cutter along the straight edge.

Move the glass out to the edge of the bench and break the strip off.

The accuracy of this method is dependent on the way you line up the glass along the edge of the cutting surface.

What is the Annealing and Cooling Relationship?

 Annealing Includes Cooling

Often people recommend a long anneal soak for potentially difficult pieces followed by an arbitrary 55C/100F cool rate to 371C/700F or 319C/600F. It is arbitrary because the same rate is frequently recommended regardless of the length of the anneal soak.

It does not have to be guesswork. Bullseye has provided us with the science of the anneal/cool in an accessible form: Annealing Thick Slabs (which covers thicknesses of 6mm/.025” to 200mm/8”). This document provides the annealing time for the chosen thickness and the directly linked cooling rates based on scientific principles.

The anneal soak is determined by the profile and thickness of the piece. Work for the e-book Low Temperature Kilnforming showed a relationship between the profile and the annealing time. Annealing for the profiles of sintering, tack, contour and full fuses requires calculation of the thickness to be applied to various profiles:

• Sinter or lamination – 2.5 times the thickest part
• Tack fuse – 2 times the thickest part
• Contour fuse – 1.5 times the thickest part
• Full/flat fuse – 1 times the thickest part

The cool stages are not random either. They have an intimate but inverse relationship to the anneal soak. They are to keep temperature differentials within the glass to acceptable levels. The anneal soak determined by the profile and thickness is to attain and keep the internal temperature within a range of 5°C throughout the glass. This is often referred to as ∆T=5°C.

The cool rates are to maintain acceptable temperature differences within the glass. The first cool rate is to maintain that temperature differential of ∆T=5°C. The second cool rate allows a wider range of temperature differential of 10°C, or ∆T=10°C. This is possible because the glass has become viscous enough to withstand this greater range of different temperature. The final cool needs to maintained at a differential of 20°C, or ∆T=20°C. Again, this is possible because the viscosity is high enough to withstand this amount of differential.

This information about cool rates and an allowable ∆T spread also indicate that turning off the kiln at 371°C/700°F is not always safe. It is almost always safe to do this for anything calculated to be annealed as for 12mm thick, and it may be safe for a piece up to 15mm thick, but remember that a tack fused piece of two base layers and a further decorative layer needs annealing and cooling as for 19mm/0.75”. The Bullseye research shows that the cooling rate for this is less than the unpowered cooling rate of many kilns. If there are additional complicating factors such as strongly contrasting colours, the annealing and cooling needs to be longer and slower than a simple multiplication of thickness.

There seems to be a practice of a single annealing rate to 371°C/700°F or 319C/600F. So the question will arise “Why is it necessary to have multiple cooling stages.” The response is that it will use unnecessary time and power. Attempting to maintain the ∆T=5°C over extended temperature ranges will not provide extra sound annealing. As the glass can withstand a ∆T=10°C from 427°C/800°F to 371°C/700°F, there is less power required at the faster rate than the slow one. This is even more so for the cool to 319C/600F and lower temperatures.

Knowing the safe temperature to turn the kiln off, requires knowing the cooling rate of the unpowered kiln. This blog shows how to determine the natural cooling rate of your kiln.  Knowing this is as important as knowing what effect different fusing temperatures have on the glass in your kiln.

The object of this blog post is to demonstrate that cooling is part of annealing. Just as much attention must be paid to the cooling rates as the length of the annealing soak. They are inseparable for sound kilnforming practices.

Some work that may be of assistance in understanding the importance of knowing the relationship between the annealing soak and the annealing cool are:

Annealing Concepts, Principles, and Practice

Available from: Bullseye and Etsy

Kilnforming Principles and Practice

Available from: Bullseye  and Warm Glass

Low Temperature Kilnforming

Available from: Bullseye and Etsy

Flat Lap Discs

Selection

Diamond discs for flat laps are expensive and the temptation is to buy as cheaply as possible. There are a number of relatively inexpensive sintered and bonded diamond steel base discs. These are acceptable up to about 220 grit, but the finer grits can leave deeper scratches. It seems to be the grit size is not closely controlled, allowing coarser grits into the bonding process. My experience is that the scratches left by the coarser grits can be worked out with more expensive, but higher quality discs of 400 grit. This allows the finer smoothing and polishing grits to produce unblemished surfaces.

Maintenance

The lap wheel needs to be free from any grit. The disc can be visually inspected for any large particles, but this will not be sufficient for smaller particles. The cleanliness of the disc can be tested by turning on the water supply to the slowly spinning disc and placing the flat of your hand onto the surface. Any grit discovered needs to be cleaned from the surface. This is especially important when using flexible smoothing and polishing discs. If you do not, you will wear away the surface of the disc, leaving bare spots.

Similarly, when grinding/polishing with a lapping disc is finished, you must ensure the disc is clean and free from any rough spots. This can be tested with your hand on a slowly turning disc. If there are grains of glass that are not cleaned at this stage they will become imbedded in the disc and reduce its useful life. Flush the surface of the disc while slowly spinning until no rough spots, especially on the outer rim, can be felt.

Then the disc can be lifted off the wheel and the bottom surface cleaned of any debris before putting aside to dry. The storage of he discs should be dry land keep dust and other contaminants off the discs.

It is not good practice to leave a disc on the wheel for longer than it is being actively used. Rust can form on the wheel and it allows debris to collect on the disc. Anyway multiple disc changes are required to go to finer grits and polishing discs, after the shaping is completed.

There are a number of good videos on HIS Glassworks which discuss the use and maintenance of grinding and polishing discs.

Is it Possible to Make Flat Laps Yourself?

A flat lap is a horizontal spinning disk to grind and polish flat surfaces onto the fired glass piece.

Many desire one of these but are put off by the expense and sometimes the space they occupy.

There is a do-it-yourself alternative that I have used.

This is to use potter’s wheels as flat laps. Table top versions are useful as they are moveable to a storage shelf when not in use. Mine was kept on a shelf until it was taken outdoors to avoid water spray indoors. They do require some adaptations and have limitations. But the great advantage is lower cost.

There are new table top ones available from £135 with a 25cm/8” turntable. This is the maximum size. They often come up second hand on ceramic and local buy and sell sites for even less.

Adaptations are required. These include:

The wheel is surface is aluminium, so a magnetic surface must be applied, as the metal discs rely on magnetic attraction to stay in place. Magnetised sheets with self adhesive backing are available to be cut and stuck to the wheel.

A water supply needs to be fixed. This can be a removable reservoir with an adjustable flow valve, or a hose from the standard water supply with a controlled flow.

The water catchment basin around the wheel does not have a drain. You can live with that and interrupt the work to empty the basin as required. Alternatively, a hole can be drilled in the basin and a Loc Line or similar system can be fixed to drain into a bucket. The waste water should not go into a drain, because the sediment will eventually block it solid. A recirculating pump is also a bad idea, because it will distribute glass grit along with the water onto the disc, and cause scratches when using a finer grit disc.

Discs must be acquired. Consider metal discs with a progressive range of grits from around 50, and doubling the grit number (halving the grit size) to around 400. I normally start with a 100 grit disc, as the coarser grits are really only for removing large amounts of glass. 100 grit can do the same job as 50 grit, but requires longer.

Inexpensive steel disks are available. However the quality of grit sizing is not always accurate, making the use of the cheaper discs with grits above 220 inadvisable. The finer grits and smoothing pads need to be of a higher quality and their expense will be justified by the lack of gouges in the later stages of fine grinding and polishing.

If you use larger or smaller discs than the wheel, you need to mark the centre on the magnetic pad, to be able to easily centre those smaller or larger discs. Of course, the smoothing and polishing pads are on flexible backings and cannot be larger than the wheel. Only the steel backed discs can be larger.

This picture is an example of my potters wheel adapted as a flat lap. The magnetic pad has been attached to the wheel, and the water supply hose and flow valve are also attached.

Rear view with grinding disc in place 

Limitations

There are limitations to this make over of course.

• The wheel surface is 25cm/8” dia. A steel plate could be attached to make the surface 30cm/12”, although centring it may be difficult.

• The speed is easily adjustable, but the top speed is around 300rpm

• The the basin is 32cm/13” diameter and its edges rise above the wheel, limiting the size of items that can be worked.

• There is no drain from the surrounding waste water basin, so drain holes may need to be added.

In spite of the limitations, this worked well for me for several years, until I had the need to flat lap large numbers of items. For those with moderate lapping needs, this is a good, low cost piece of equipment.

Peptides as a Glass

 Peptides as a glass. Thanks Susan Walpole for the link to a YouTube video.

youtube.com

A glass that builds and heals itself

Researchers have discovered that a peptide, when mixed with water, can self assemble into a rigid 

Crate for a Travelling Exhibition

 

I was accepted along with others on the basis of a proposal to exhibit with a travelling exhibition organised by the Scottish Glass Society.

This will be packed and unpacked by other people at least four times during the exhibition year. My experience with helping to pack up the Collect work exhibited by craftscotland showed me the need to prepare the packing properly.

I decided to build a crate with custom fittings to cushion the work from any damage. I felt when I finished that it was such a simple arrangement that others may benefit from a description of what I did.

The crate can be made from a variety of materials, of bourse, but wood is easiest for me.  I used some plywood offcuts to form the base and sides.  The ends were formed from 3 ply plywood with 19 by 45mm timber cut and nailed to it.

The side rail does not have to be so large as I made it - just too lazy to cut it down. The side rail allows the top to be screwed to the sides holding them from expanding or bowing with the pressure of the packing materials.

I then cut 50mm thick polystyrene sheets to fit the case. These were attached together with "U" shaped copper wire stuck into them. The shape to fit the glass was cut with a heated cutting tool. It is a bit smelly and smokey, but does the job. When the shape for the glass was formed, a 10mm sheet had a collar cut out to go around the rim of the glass.

Note that the packaging is also numbered so that each piece is put back into the crate in the order required for transport. When the base layer and cradle for the glass are placed in the bottom of the crate, the glass is added.

Now the crate is ready to have the wooden part of the work packed. This shows the piece with the glass in the wooden cradle with the packaging around the "slipway".

The packaging for the "slipway" is put into the crate separately from the glass and packaging. You can see there is a layer of polystyrene between the glass and the wood.

Then the "slipway" is inserted into its cradle.

The polystyrene had holes made with the hot cutting tool to correspond to the supports for the glass. The holes are larger than the supports, so there is no pressure on them during transport.

Again the packaging is numbered. The final packing pieces are to be added now. Still each has its number!


The major pieces of packing are now added ready for the topping out!

Next add the essential tools and spares. In this case the tool is a two way spirit level so the piece is placed horizontally and level.

Then there is the necessary photo to show how the piece is to be displayed.

Finally the list of contents and instructions on installation.



Now the lid can be put on and screwed down. Note the locating marks on the lid to show how it fits without having to run new pilot holes for the screws. The screws to be removed are noted with an "X".





Screwing together to be solid and ready for delivery.





If the instructions are followed everything should be secure for delivery to the buyer!

P.S:  It came back in one piece. Unfortunately it did not sell during the exhibition, but it did later.

Is Vertical Crescent Attachment Possible?

“I want to tack fuse [6mm thick crescents to] stand erect...[on] a base. I need help thinking this through. … Is there a way to fuse them erect without forming a puddle of glass?”

It is correct that at tack fuse the crescents will deform. It is, after all, above the slump temperature.

You could use fibre blanket packed between the crescents arranged in a fan formation. This requires assembly on the kiln shelf. If you allow them to touch at the pivot point, they will stick to one another during the firing.

Use a sinter firing. It will be something like:

• 65°C/ 117°F to 670°C/ 1236°F for 6 hours.

• The anneal soak should be for 5 hours at the appropriate temperature. The associated cool is at 11°C/ 20°F to 427°C/ 800°F, 0’;

• 20°C/ 36°F to 427°C/ 700°F, 0’;

• finally at 52°C/ 117°F to room temperature.

This arrangement and firing will enable the crescents to be securely attached to the 6mm base with a minimum of distortion.

More information is available in my e-book Low Temperature Kilnforming, available from:

• Bullseye

• Etsy

• and   stephen.richard43@gmail.com

Stress Testing - How?

 This is a presentation I gave a while ago on why and how to test for stress without risking the piece, that is, non-destructive testing.