What are the main weaknesses of the existing UHMWPE ski base types? – Part V.

Fifth issue of the existing UHMWPE ski base types is their very low ability to bind gliding ski waxes and other gliding agents chemically.

How it works?

Chemical bonds between UHMWPE and wax-based gliding agents are very weak, chemical bonds between carbon black as main structural and reinforcement additiv in modern ski base types are extremelly weak. In other words: if applied on a ski base, wax-based gliding agents cannot rely on chemical bonds, they urgently need mechanical retention.

Mechanical retention is strongly depending 1. on available free spaces or cavities in both very top surface and in bulk material of the ski base, 2. on size and disponibility of these free spaces and cavities = they are avaibale in amorphous and transition areas only, many of them are occupied by soot and other additives), 3. on size and charakter of the wax molecules which need to get inside free spaces when base material is more flexible thanks to heat and get stuck there when base material cools down again, 4. on the level of intertwining of the molecular chain structures of both ski base material and wax-based gliding agents.

Maybe the last forth condition is the most significant one for how strong the final mechanical retention of waxes in the ski base is. At the same time this forth condition = the level of intertwining of the molecular chain structure of ski base material on the one side and ski wax substances on the other side is the most problematic and tricky one.

Why?

For wax-based gliding agents very strong dependency exist between hardness and strogness of intertwining on the one side and softness and weakness of intertwining on the other side. This very strong dependency is defined by the length and charakter of the molecular chains of wax-based gliding agents.

The longer and more branched the molecular chains of the wax-based gliding agents are, the stroger they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the stronger is their mechanical retention inside the ski base material.

The shorter and less branched the molecular chains of the wax-based gliding agents are, the weaker they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the weaker is their mechanical retention inside the ski base material.

At the same time the length and charakter of the molecular chains of wax-based gliding agents define their gliding properties.

The longer and more branched the molecular chains of the wax-based gliding agents are, the stroger they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the stronger is their mechanical retention inside the ski base material, the worse gliding properties.

The shorter and less branched the molecular chains of the wax-based gliding agents are, the weaker they can be intertwined with extremely long molecular chains of the ski base material (UHMWPE), thus, the weaker is their mechanical retention inside the ski base material, the better gliding properties.

Waxes with best gliding properties does not stick to ski base material, the better waxes stick to ski base material, the worse gliding properties they have. Good advice is better than gold.

What are the main weaknesses of the existing UHMWPE ski base types? – Part IV.

Forth issue of the existing UHMWPE ski base types is their low and uneven capacity to take and hold other substances as gliding ski waxes and agents.

How it works?

Only sintered ski base types have sufficiently long chains to create free space to take wax molecules on the very top surface and inside the bulk material.

On the very top surface we call the free spaces “flokati carpet” which are fibres or hairs several hundred nanometers long which are covering the entire ski base surface. Between these fibres is enough space for wax molecules get in and get stuck here. Most wax molecules are allocated here.

In bulk similar free cavities do exist because the bulk material consists of intertwined molecular chains. It is estimated that wax can penetrate the ski base up to 1 micrometer, thus 1000 nanometers, the deeper you go, the less wax molecules you will - however - find.

Both free spaces in flokati carpet on the very top surface and free cavities inside the bulk material are ca. tens of nanometers large which means there is enough space for wax molecules  but...

If we connect this knowledge about size and distribution of free spaces or cavities in the flokati carpet on the very top surface and in the bulk material of the ski base with the knowledge about how especially competetion skis are prepared (several basic wax layers applied as hot appoach, gliding layers applied as block waxes or powder waxes, top coats applied as liquids or sprays), we need to see / understand that the spatial capacity of free spaces and cavities which was available at the very beginning of the ski service process is consumed very fast and each new layer applied on the ski base creates more and more complex mixture than a new layer.

If we combine these types of knowledge about size and distribution of free spaces or cavities in the ski base and about competition ski service processes with the chemical interaction between PE / carbon black as main material components of the ski base on the one side with waxes and wax-based gliding agents on the other side (chemical bonds between ski base and waxes are extremely weak and waxes need to rely on mechanical retention inside the ski base) it must be absolutely clear to us that existing services processes in combination with existing ski base types cannot create any relyable / repeatable and controlable results.

Combination of the existing ski base types and existing ski service processes cannot result in relyable / repeatable and controlable gliding features on the ski base.

What are the main weaknesses of the existing UHMWPE ski base types? – Part III.

Third issue of existing UHMWPE ski base types are the fast changes of the ski base surface.

How it works?

We know that the main component of UHMWPE ski base types is PE with extremely long linear molecular chains (normaly 7 to 12 mil. g/mol) which is enriched with different additives where the most important is soot or carbon black.

Even if we speak about PE with extremely high molecular weight and about carbon black as singular material types, we need to understand that there are plenty of PEs and carbon blacks which very different and specific features.

Particular features of PE and carbon black as two main components of modern ski base types define how they interact if processed in sintration. Normally carbon black has low or no chemical interactions with PE matrix leading to pure “sitting” inside the PE matrix. This weak “sitting” of carbon black corns inside the PE matrix results in fast and easy “breaking out” of whole soot corns out of matrix, “breaking off” of soot corn parts or soot corns abrasion on the very top surface. All these processes - breaking out / breaking off / abrasion - result in quite fast microscopic changes of the very top surface. These changes are the faster and more significant, the larger and more complex the very top surface of the ski base is, i.e. complex structure patterns which enlarge the surface multiple times and create complex details accelerate these changes.

Due to very weak chemical interactions between PE matrix and carbon black the very top surface of the ski base is a subject of very fast - even if with the naked eye invisible - microscopic changes which do cause that skiers run on a new ski base surface latest in the next competition.

What are the main weaknesses of the existing UHMWPE ski base types? – Part II.

Second issue of existing UHMWPE ski base types is the ski base memory of gliding waxes.

How it works?

Only sintered ski base types have sufficiently long chains to create free space to take wax molecules on the very top surface and inside the bulk material.

On the very top surface we call the free spaces “flokati carpet” which are fibres or hairs several hundred nanometers long which are covering the entire ski base surface. Between these fibres is enough space for wax molecules get in and get stuck here. Most wax molecules are allocated here.

In bulk similar free cavities do exist because the bulk material consists of intertwined molecular chains. It is estimated that wax can penetrate the ski base up to 1 micrometer, thus 1000 nanometers, the deeper you go, the less wax molecules you will - however - find.

Both free spaces in flokati carpet on the very top surface and free cavities inside the bulk material are ca. tens of nanometers large which means there is enough space for wax molecules on the one side but there are not accessible by any mechanical cleaning process on the other side.

Wax cleaners can reach these free spaces and free cavities but to remove all wax which has entered these nano-spaces in liquid state and solidified here is hardly possible.

These wax residues which cannot be removed any more after they have entered the free nano-spaces in both flokati carpet on the very top surface and in the bulk material we call ski base memory.

What are the main weaknesses of the existing UHMWPE ski base types? – Part I.

It is well-known that competition skis are equipped with UHMWPE ski bases where PE with ultra-high molecular weight = ultra-long molecular chains is enriched with different additives, first of all carbon black.  

UHMWPE is a type of material which is difficult to be processed. The longer the molecular chains, the more problematic the process-ability. One of the few possible processes is sintration. PE in granular form is mixed with soot and other additives and sintered with help of heat and pressure to a coil which is cut to a continuous strip which is grinded and flamed

 

Here the first issue of the existing UHMWPE ski base types originates. The coil has normally a diameter of ca. 1,5 m, the steel form is cooled down from edge to centre resulting in faster cooling of outer coil areas and slower cooling of inner coil areas. Cooling speed is directly influencing the fraction of crystalline and amorphous areas or ordered and disordered molecular structure. Molecular grid arrangement (crystalline and amorphous) is directly influencing the mechanical features and ability of the ski base material to create free cavities = to take additionally applied gliding waxes.

Only amorphous and transition fraction can take additonally applied wax. Crystalline fraction cannot be entered by any wax at all.

 

Each ski base surface revealed by each grinding is an original with a unique arrangement of crystalline, amorphous and transition fractions.

Why no wax chemistry has appeared?

No-wax chemistry is a clear reaction of the wax industry on the extremely low life time of liquid waxes based on dissolved waxes. 

The life time of waxes applied on the ski base is quite low in general. Due to very weak chemical bonds between waxes and PE, waxes need to rely on mechanical retention inside the ski base. Only waxes which can penetrate the ski base – or better: free cavities in the amorphous regions – can be retained more strongly providing longer life time.

Waxes sticking to the very top surface of the ski base – with no retention inside the ski base – can last for an extremely short time.

 To make waxes penetrate the ski base, more pre-conditions need to be given:

•  ski base material needs to have free cavities to take waxes
• heat needs to be introduced to increase the mobility of ski base material and liquidize the waxes
• wax filled cavities need to shrink after cooling to retain wax mechanically

·          As you can see the standard liquid waxes where the gliding agent is dissolved in a fast-evaporating carrier do fulfil only a part of one condition needed for a strong mechanical retention = they are liquid…that’s all…

The idea that liquid waxes can penetrate the ski base material due to the liquid status does not work in reality because especially the heat induced effects are completely missing.

To replace the heat approach and keep liquid waxes application as simple as possible, alternatives have been searched for to improve the mechanical retention of liquid waxes and thus their life time.

The clear answer is no-wax chemistry = gliding agents in a carrier which helps to penetrate the ski base.

To penetrate the ski base etching or swelling approach is often used. To fix the gliding agent in and on the ski base special carriers are used which can connect with both PE and gliding agents.

No wax chemistry is the approach how to keep liquid gliding agents application simple and to achieve a reasonable life time of liquid gliding agents… With waxes it is – however – hardly possible, that’s why no-wax chemistry…

 

What is the main difference between the cheaper and more expensive liquid gliders

Normally the main difference is the life time / stability / wear resistance… in other words how long the improved gliding properties can last under given snow and weather conditions.

 

Normally the cheaper liquids last on the ski base for a much shorter time and therefore provide a much shorter improvement of gliding features.

 

Why? Most of the cheaper liquid gliders are solutions containing two main components: active ingredients dissolved in a carrier. The carrier is responsible for liquid state of the solution, enables application on the ski base in the liquid form. After application the carrier evaporates more or less fast and leaves only the solid component on the ski base.

 

The only way how this solid component sticks to the surface of the ski base is the mechanical retention in the microscopic irregularities and roughness of the ski base surfaces. The chemical bonds are extremely weak.

 

How cheaper liquid gliders can be identified?

 

·      You need to shake the bottle before you properly to mix the active ingredients with the carrier.

·      Often sponge head is used for application.

·      After application you can see a wet film on the ski base.

·      They dry quite fast (5 to 10 min.)

·      You need to brush them softly with nylon brush.

 

Normally the more expensive liquid gliders perform a bit better, but especially last longer, in other words provide the improved gliding features for a longer time.

 

Why? Most of the more expensive liquid gliders contain a component which actively disrupts the surface of the ski base in a gentle way, in other words which allows the active substances in the glider to soak or to be integrated into the ski base. In other words: more expensive gliders create their own irregularities or micro roughness for better integration into the ski base.

 

How more sophisticated liquid gliders can be identified (except for they are more expensive)?

 

·      Normally they are sprays – you spray them or apply with fleece.

·      After application they often create small bobbles on the surface.

·      They need more time to dry / be integrated (normally 25 min. to 30 min.)

·      Often they are not brushed.

Which components of the ski base are the most important

 

 

Even if specialized magazines and articles mention many different additives and ingredients used in ski bases of competition skis, finally we will find out, if we look in much more detail, that there are only two main components which influence the most important features of each ski base type, especially now after fluor ban.

 

First is the UHMWPE itself which defines the features of the matrix. The matrix itself can get touch in contact with snow surface, that’s the reason why PE is used, because currently there is no other polymer with such a low coefficient of friction and so high hydrophobicity available. With respect to other components the matrix is responsible for the wear resistance and fixation of additives.

 

For wear resistance the most important figure is the length of molecular chains, the higher the length of molecular chains, the better the wear resistance. Reaching the value of 10.000.000 the polymer can be hardly processed.

 

Additive fixation in UHMWPE is problematic. The most additives do not form strong chemical bonds with the base matrix. Additives are bound in the matrix either by very weak chemical bonds or by mechanical retention. Especial close to the surface where the contact snow and ski base surface take place especially the mechanical retention decides.

 

The most important additive used in modern ski base types is soot or carbon black. The importance is given by the amount used in the competition ski base types which reaches up to 20 % of weight fraction in Nordic skis and up to 40 % of weight fraction in Alpine skis and by the way how carbon black is fixed in the PE matrix.

 

Some carbon black is incorporated directly in the PE matrix, but most of carbon black is filling the free space or cavities between the PE corns which are sintered together using heat and pressure. Especially the second type of soot fixation is responsible for high values of E-modulus which decides how ski base changes elastically under load.

 

Wax history in the ski base

We know that the very surface of the UHMWPE ski base is created by crystalline, amorphous and transition regions. In crystalline regions no wax can penetrate, transition regions are insignificant with respect to the area, the only ski base fractions where wax can penetrate are amorphous regions.

Amorphous regions consist of disordered structure of PE molecular chains with free cavities which size is in the order of tens of nanometres. In these free cavities there is enough space for wax molecules to get in and get stuck after hot wax application.

If ski base is ironed by temperatures close or above the melting point of UHMWPE which is ca. 140 degrees C the molecular chains of UHMWPE become more flexible and the free spaces between the chains are more easily to be accessed by wax molecules. After the ski base has cooled down again, the molecular chains “freeze” again and wax molecules remain trapped in the nano-cavities.

After skiing wax removers and cleaning brushes are used. Current wax removers evaporate very slowly which means their molecules are larger and heavier than those which were used in the past. They can access the cavities and dissolve the wax, however, they cannot remove the mixture out of the cavities.

Brushes are too coarse to reach the cavities. Some amount of wax - dissolved by removers - will remain in the cavities. After wax removers evaporate, solid wax remains in the cavities. This wax will stay here, until new wax is applied and mixed with the wax history in the ski base.