French researchers develop 'self-healing' rubber

Paris - A group of French researchers has published a paper on self healing rubber  in the

prestigious science journal, Nature (Vol 451, 21 Feb 2008) today. The paper is titled, Self-healing and thermo-reversible rubber from supramolecular

assembly and describes a type of rubber which can survive small cuts

repeatedly. These small cuts can repeatedly heal themselves at

room temperature.  The researchers say the rubber is based on fatty acids and urea.

In the paper, the researchers say, "In striking contrast to

conventional cross-linked or thermoreversible rubbers made of

macromolecules, these systems, when broken or cut, can be simply

repaired by bringing together fractured surfaces to self-heal at room

temperature."

The self-healing happens spontaneously when two freshly cut surfaces

are brought together. The cut surfaces begin to merge almost

immediately. Even after around 15 minutes, says the paper, the

materials can withstand strains of 100 to 200 percent. The healing then

continues over the following three to four hours. Following the

self-healing, the samples regain the potential to deliver strains of

several hundred percent with low creep, claims the paper.

At room temperature, self-healing is no longer possible after a week or

so. This interval reduces rapidly at higher temperatures, to about 48

h waiting time at 40C, 95 min at 60C, 15 min at 90C, and 5 min at

120C.

The lead author on the paper is Philippe Cordier at Ecole Superieure de Physique et Chimie Industrielles (CNRS-ESPCI) in Paris.

The paper describes the production method thus: "Compound A is obtained

at the 100 g scale in two steps. 175 g of Empol 1016 supplied by Cognis

(mixture of 4% monoacid, 79% diacid, 17% triacid and polyacids) was

condensed with 70.3 g of diethylenetriamine at 160C under nitrogen over

24 h. 72 g of oligo-amidoamine with a [CH2-CONH] to [CH2-NH2] ratio of

1.8 as determined by NMR obtained after elimination of unreacted amine

(chloroform/water extractions) was then reacted with 17 g of urea at

135-160C for 7.5 h under nitrogen, whereupon ammonia and unreacted urea

were extracted by vacuum stripping and water washings. The material was

dried under vacuum and pressed at 120C into steel moulds of 100 cm² area

at 32mm depth. Swelling with dodecane was achieved at 60C over 24 h."

Story at Nature magazine