Europeans discovered the special properties of the milk from the latex tree Hevea brasilensis in the 15th century. The natives of South America had been aware of the properties of latex for a long time before that. They called the rubber tree “cahuchu” which meant “weeping wood”; the French, who can only speak one way, came up with “caoutchouc”.
Our latex milk is a white, natural caoutchouc based dispersion which hardens in the air (dries), stabilizes with ammoniac and is already vulcanized. Vulcanization is the process by which the linked chains in the caoutchouc which are not chemically bound are provided with crosslinking. In the case of natural caoutchouc it is, for example, sulphur vulcanization whereby the sulphur molecules perform the crosslinking function. The number of sulphur bridges determines the final hardness of the rubber.
Latex milk is used industrially in the production of medical consumable materials (e.g. GLOVES, catheters), baby dummies, condoms or toy balloons. As a moulding material it is very economical but does have some disadvantages: working with it can take a long time and is fairly involved and it can really only make relatively thin flexible moulds. Cured latex is indeed extremely elastic and tearproof but will tend to continue to tear further once a tear has begun.
Storage and Shelf Life
As a natural material with practically no additives, latex is, on the one hand, a very agreeable material but, on the other, it is not as durable as synthetic rubbers or silicones. It is not UV resistant and reacts strongly when coming into contact with cleaning agents that contain solvents as well as oils, grease or metal compounds containing copper. Latex moulds are longer lasting if, after use, they are rubbed with Talcum-powder because this will prevent the latex from sticking to itself. When being stored for longer periods this process should be occasionally repeated.
In its liquid form, latex should be stored in air-tight plastic or stainless steel containers at temperatures between +5 °C and maximum 35 °C. Under ideal conditions (20 °C), uncured latex can be stored for at least 24 months.
Safety at work
Despite the tiny amount of NH3 (approx. 0.3%) you can still smell ammoniac when working with latex. Other than the usual precautions taken when working with any chemicals, however, no special measures must be taken. Latex milk does not fall under the hazardous material ordinance and does not require a German hazardous material label.