formaldehyde - Sciencemadness Dot Org

356
FORMALDEHYDE
In addition, it is stated to have a lower viscosity than the usual pale crepe
or smoked sheet rubbers, and an improved resistance to abrasion.
Patents indicate that formaldehyde may also be used as an agent for
gelling and coagulating dispersed rubber compositions. Hayes, Madge and
Lane ic obtain a dispersion capable of rapid gelling at ordinary temperatures
by adding excess formaldehyde to an ammonia-preserved latex to which
sulfur, zinc oxide, accelerators, etc., have been added. It is stated that
articles can be prepared from this dispersion by spraying, impregnating or
spreading on forms, etc. To obtain the desired results 0.3 to 1.0 per cent
formaldehyde in excess of the amount which reacts with ammonia must be
added. Gelling is also accomplished by adding phenol prior to the addition
of formaldehyde 11 . According to Woodruff 88 , increased yields of a rubberlike
coagulum may be obtained from latex by addition of a water-soluble
gum and dispersed mineral oil, which act as extenders, and then coagulating
with formaldehyde. Blatel- 5 produces a self-coagulating vulcanizable
bath of latex by addition of an ammoniacal solution of zinc acetate mixed
with a water-dispersion of colloidal sulfur containing casein and formaldehyde.
Xeiley- 4 produces rubber articles by dipping forms into an ammonia-stabilized
latex composition containing sulfur, antioxidants, accelerators,
etc.. plus a potential coagulant such as zinc ammonium chloride,
and then immersing the coated forms in a solution of formaldehyde, which
reacts with the ammonia stabilizer and activates the coagulant. Threads
are formed from aqueous rubber dispersions containing glue which have
been subjected to a formaldehyde treatment 30 .
Rubber Derivatives. Formaldehyde probably reacts with rubber in
much the same manner that it reacts with other unsaturated hydrocarbons
(pages 227-230). In 1923, Kirehhof 34 obtained what he designated as
rubber-formolite by reacting pale-crepe rubber dispersed in petroleum ether
with sulfuric acid and then heating with formaldehyde. The product
after treatment with hot water and ammonia was a yellow-brown powder
which decomposed without melting on being heated, swelled in carbon
bisulfide and pyridine but did not dissolve in water or related solvents.
Approximately 2 g of rubber-formolite were obtained for each gram of crepe
rubber. Related processes involving controlled reactions of formaldehyde
and rubber under acid conditions yield various forms of modified rubber.
According to MeGavack 16 , a product similar to hard rubber may be obtained
by the action of formaldehyde on rubber in the presence of sulfuric
acid. A patented adhesive for bonding rubber or rubber-like products to
metal, glass or hard rubber may be prepared by the action of formaldehyde
or paraformaldehyde on rubber dispersions in ketones such as cyclohexanone?
camphor or benzophenone 31 .. Products ranging from soft, tacky
materials to hard resins are described in a German process 13 involving ap