Plastics keep a close watch
Polymer lifejackets for sailors overboard
Polymers are particularly suitable for wet environments because they are entirely resistant to corrosion and putrefaction. Sailors know that they can always count on them, especially when the wind blows stronger and the sea rages. The first image that comes to mind is that of the essential and emblematic lifejacket that it is prudent to wear as soon as you step on a boat. Its role is simple: ensuring the buoyancy of a crew member who has fallen into the sea until they can be recovered. Recovery may take some time during which the crew member who has fallen overboard may well succumb to exhaustion, especially if the sea is rough and cold. The lifejacket is not a recent invention since the first patent dates back to 1765. At that time, it was made up of an assembly of pieces of cork tied together with strings. Although it was effective in the event of falling overboard, it was cumbersome and made it difficult for sailors to move when manoeuvring on deck. For this reason, it was rarely worn and therefore did not make much of a difference in the number of people missing at sea. More than a century would pass before the lifejacket was modernised, becoming a cotton jacket lined with pieces of cork. This was the type of lifejacket taken on board the Titanic, although unfortunately in very insufficient quantities. Cork, which was considered too cumbersome, was replaced with kapok, a vegetable fibre. This was a marked, but not entirely satisfactory, improvement because kapok tends to lose its buoyancy when compressed. The real revolution came during the Second World War with the first inflatable lifejacket. Adopted by the American army, it consisted of a rubber bladder inserted into an oiled canvas casing. Inflating it simply required striking a small bottle of compressed CO2.
Modern inflatable lifejackets are designed not to hinder crew members' movements. This is all the more important on racing boats where it is often necessary to react at very short notice.
For the record, the soldiers gave this lifejacket the nickname of Mae West, a famous actress of the era known for her generous figure. Modern lifejackets owe it everything and since then, it has never stopped evolving. The use of modern polymer materials has made it possible to reduce its weight and improve its ergonomics. For manufacturers, the aim is certainly to save lives, but also to do everything possible to ensure that the lifejacket is as unobtrusive as possible, an essential condition, especially for sailors who often have to contort their bodies to perform manoeuvres. Thus, current lifejackets are extra thin; they are generally woven from ultra-resistant synthetic materials such as polyester. As for the bladder, it is made up of an assembly of glued PVC parts. PVC, which is perfectly watertight, is easy to cut and makes it possible to design a device that will keep the user floating and keep their head out of the water. In addition, the material is flexible enough not to burst when the CO2 bottle is struck. Finally, top-of-the-range lifejackets are equipped with a beacon that sends a signal to the lifeboat. Since it is filled with electronics, it must be perfectly watertight to ensure that the sensitive electronics do not to come into contact with seawater; that is why those components are fitted inside a polypropylene case.
Paddleboard and canoeing enthusiasts now have a floatation device adapted to their activity.
Manufacturers have also considered smaller models to meet demand from paddleboard and canoe/kayak enthusiasts, a growing leisure activity often practiced in calm waters in the summer. However minimal, the danger of drowning is very real. Spinlock, an English manufacturer, has designed an inflatable lifebelt which is ideal for this type of activity usually performed in a swimsuit. It comes in the form of a small bum bag that is worn around the waist. The lack of straps means that it is entirely unobtrusive.
Based on the principle and polymers used in inflatable lifejackets, this lifebelt can be inflated by pulling on a cord connected to a bottle of CO2. It is more of a buoyancy aid than a real flotation device designed for survival at sea. Nevertheless, it is more than enough to help the user get back to the paddleboard or canoe that has been carried away by the current without fatigue.
Lifebelts: plastics, of course
Although European regulations do not require crew members to wear lifejackets at all times (only some regatta organisers may require this), it is mandatory to have them on board as well as various floatation devices. In this field too, polymers have become a mainstay for obvious reasons. For example, the famous orange lifebelts generally found hanging at the back of recreational boats have a polyethylene structure filled with polyurethane foam.
Proof of the effectiveness of the combination of polyethylene/polyurethane is that the design of lifebelts has not changed in recent decades. These plastic lifebelts can be found on all types of ships all over the world.
Other recreational sailors prefer polyurethane foam models wrapped in a PVC cover for their weight and flexibility. The latter, weighing less than 1 kg, guarantee a buoyancy of about fifteen kilograms, which is more than enough to keep the head and shoulders of the unfortunate crew member who fell overboard out of the water. Last but not least, these lifebelts are connected to the boat by a polypropylene line, a material that floats perfectly. Even just a few grams less below the surface of the water means better buoyancy.
That being said, the ideal situation remains not falling into the sea, especially when the sea is rough. Cautious sailors consider it advisable to tether themselves to the boat using a lanyard made of polyester, the material used to make seatbelts. Such strong and lightweight lanyards are unobtrusive, especially when they are fitted with two carabiners such as those used in mountaineering and climbing.
When life hangs by a thread…of polymer
Recreational activities in the mountains, especially mountaineering or climbing, are among the most dangerous. Its practitioners, wrongly considered "risk takers", are aware of this and are very fussy when it comes to their safety, which also depends on the quality of their equipment. Manufacturers closely follow the evolution of polymers in order to offer high-tech products. Ropes are a perfect example of this. For uninitiated, a rope is a rope, and nothing sets them apart save for their colour. In reality, a world of complexity lies below the surface. In short, there are two types of rope: dynamic and static. The former is mainly used in climbing or mountaineering. They are called dynamic because they can stretch by up to 40% in the event of a fall. This elasticity is a decisive safety element because it helps to cushion the impact that could be fatal to the climber in the event of a fall. Top-of-the-range models are made of polyamide, a material that is both resistant and elastic. It should be noted that climbing schools that train students at low heights use ropes made of polyester or polyethylene, materials that are elastic but more sensitive to wear and tear, for cost-related reasons. A rope consists of two parts: the core and the sheath, the latter being designed to protect the former.
Mountaineering ropes and climbing ropes are made from different polymers to meet very strict safety standards because they are the last line of defence against fatal accidents.
At the time of manufacturing, the ropes are braided and all the manufacturers' know-how is put to use with the aim of finding the ideal density level to guarantee a good strength/elasticity ratio. Experts judge ropes on this characteristic alone. Finally, the fibres can also be treated with different additives to make them hydrophobic and prevent snow or ice from entering the rope, which could make it heavier or even degrade it. Static ropes, on the other hand, are very inelastic and are very useful for lifting an injured person, for example. Their main advantage is their resistance to abrasion and wear. For this purpose, they are woven from PPD-T (poly(p-phenylene terephthalamide)) or UHMP (ultra-high molecular weight polyethylene) fibres, better known under their respective trade names of Kevlar© and Dyneema©, which are resolutely high-tech and high-performance polymers.
Plastics guarantee a good foothold
As sailors have their lifejackets, so do mountaineers have their harnesses. The analogy may seem a strange one, but they share the same constraints: they must be as unobtrusive as possible in order not to hinder movement. The comparison does not stop there, because both are real feats of technology designed to improve ergonomics. For example, the harnesses that fit around the waist and thighs are made of high-tenacity polyester, a polymer that is able to resist abrasion and UV rays. For the climber's comfort, they are most often lined with cross-linked polyethylene foams, a plastic that is difficult to tear, super light and particularly flexible. The straps and hanging systems are made of Kevlar© or Dyneema© chosen for their extreme strength.
For mountain sports, there are insoles adapted to each type of terrain. Their properties differ depending on the design of their studs and their flexibility. Polymers are the big winners because they are the only ones that can adapt to all situations.
Plastics and other polymers have also become a guarantee of safety in many other products such as helmets that are as light as they are strong thanks to expanded polypropylene or polycarbonate, for example. Although less spectacular, shoes also contribute to the climber's peace of mind and it is to plastics that we owe the greatest progress, especially in the field of soles. EVA (ethylene-vinyl acetate) soles in particular are very popular. EVA is a particularly flexible material that works on all types of terrain and is insulating enough to keep the foot dry or even warm.
Like many polymers, it is easily moldable, which makes it possible to design a sole profile adapted to different types of terrain (soil, snow, rocks, etc.). This is a crucial detail as the main role of a mountaineering sole is precisely to adhere to the ground in order to avoid slipping which may have unfortunate consequences. Combining comfort with safety is the ultimate goal and that is why manufacturers have chosen polymer materials for the job. Rescue workers have also made the same choice in this area.