Mobirise

Materials

rapstrap use the following polymers to minimise environmental impact

Polyurethane (TPU)

Strong & Flexible

Developed by Otto Bayer in the 1930s as a response to Du Pont's introduction of nylon.
TPU is a tough and durable elastomer.

Fire Retardant TPU

Self-Extinguishing

The addition of halogen-free flame suppressants can achieve a UV-94 V2 fire rated TPU with low smoke emissions.

Polycaprolactone (PCL)

Biodegradable

Rapidly digested by microbes (mostly fungi) when exposed to dirt and moisture. PCL readily degrades even in cool environments.

Poly Vinyl Alcohol (PVOH)

Water Soluble

Developed by Staudinger in 1924 and later commercialised by Sakurada at Kurashiki Rayon.
Dissolves in cold water in just a few hours.

Specialities

PA11, PVC, TPE

Using a wide variety of specialised polymers, rapstrap continue to develop custom products for many diverse applications.

Thermoplastic polyurethane (30% recycled)

TPU is one of the strongest elastomeric polymers available. It can be produced in a variety of different grades ranging from extremely soft & flexible, to fully hard & rigid. Our standard range of Classic and i-Tie rapstraps are made using a relatively soft TPU (90A shore hardness) currently supplied by Coim S.p.A. in Milan. At least 30% of the material we use is recycled.

Please note that because the rapstrap Classic is designed to offer maximum elasticity, they are only available in this 90A material.

However, our second-generation rapstrap i-Tie is designed to use much stiffer grades of polyurethane, typically up to 60D hardness. A fire-retardant (UL-94 V2) TPU is also available for this product.

Thermoplastic polyurethane rapstrap cable ties
Raw fragments of reclaimed PVC cable sleeving

Poly vinyl chloride (100% recycled)

Fully recycled PVC (taken from old cable sleeving) offers a 100% recycled alternative to our standard TPU rapstraps. This material can be used to produce heavy duty versions of the rapstrap Classic, and we have also successfully produced rapstrap i-Ties using it.

By itself, this reclaimed PVC material is not sufficiently elastomeric to produce a convincing rapstrap, so we blend it with around 25% recycled TPU to compensate.

This is unusual, as most polymers cannot be simply mixed together like this. But surprisingly, the resulting polymer alloy is almost as strong as pure TPU. Furthermore, it's more weather-resistant than standard TPU, and the high PVC content offers better chemical resistance in acidic environments.

Polyamide 11 (renewably resourced)

Developed in France in the 1940s, PA11 ("nylon 11") is a renewable resource bio-plastic made from castor oil*. It is softer and more flexible than other types of nylon, but somewhat stronger and stiffer than even the hardest grades of TPU. It is widely used for pipes, hoses and other tubing applications.

Although expensive to produce and not as strong as nylon 66, PA11 does exhibit superior weather-resistance. It offers low moisture absorption and is quite tolerant to UV-exposure. (Only the very expensive fluoropolymers are better in this respect.)

To exploit this useful property, rapstrap have developed a custom PA11 variant of the i-Tie that's intended for long duration outdoor use, particularly for cable management applications on solar farms.

(* Note that although PA11 is a bio-plastic, it is not biodegradable.)

Renewable resource polyamide 11 i-Ties
Rapstrap i-Tie made from biodegradable PVOH glue

Poly vinyl alcohol (biodegradable)

PVOH is a water-soluble and fully biodegradable polymer that's normally used as a glue or binding agent. (It's also the component of PVA adhesive that cross-links with borax to produce "slime".)

Although not common practice, certain grades of this polymer can be successfully injection moulded, and this has allowed us to create a novel waste-free and rapidly disposable version of our i-Tie. These PVOH rapstraps are very flexible and semi-elasticated, but are (understandably) not quite as strong as our standard TPU versions.

In dry conditions they have proven to be quite stable over long periods, but once in contact with water, our PVOH i-Ties rapidly start to swell and will dissolve completely in a few hours.

Even undiluted, the resulting gloop is readily consumed by microbes over a period of a few weeks. As seen here, dissolved rapstraps "go mouldy" as microbial colonies form in the gel. The black residue is the resulting bio-mass left by the digestion process.

Polycaprolactone (biodegradable)

PCL is one of the most readily biodegradable plastics currently available. It was first reported by Frank van Natta, Julian Hill, and Wallace Carothers in the mid 1930s, and is known to biodegrade under both aerobic and anaerobic conditions, including in freshwater, marine and landfill environments.

Unfortunately it's too weak to produce a standard rapstrap, and too soft to work as a conventional cable tie - we tried both!

So to make use of this material, we went back to the drawing-board and tried over 30 prototypes until we had a new cable tie design that worked.

The resulting PCL cable ties have been shown to start biodegrading after just a few weeks when buried in common garden soil at temperatures of 10-20C.

Biodegradable Polycaprolactone cable ties
Biodegradable TPE rapstrap tree ties

Thermoplastic elastomer (bioplastic)

TPEs are a broad class of polymer that include the thermoplastic polyurethanes and the synthetic rubbers. 

Using a custom biodegradable TPE suppled by Wittenburg - and working in conjunction with Biodegradable Plastic Products Ltd - rapstrap now offer a range of biodegradable tree ties to compliment our existing product line.

This specialist material has mechanical properties somewhat similar to a TPU, and provides all the strength and flexibility necessary for successful tree management over a 3-5 year period. However, it has also been engineered with a high starch-based content to promote gradual degradation over a longer period.