entering a new era that may lead it during the next decade into an even m ore enviable position in the hosiery industry, into a variety of fine fabrics, plastic products and many other fields.— Editors
O
n O c t . 27, 1938, the E, I. du P ont de Nemours & Co. announced to the world the developm ent of a group of new synthetic super polymers from which, among other possible applications, textile Sbers could be spun surpassing in strength and elasticity any previously known. T h e polyamide from hex- amethylene diamine and adipic acid first synthesized bv the research workers of the D u P ont company in February, 1935, was con
sidered the most promising, both from the standpoint of its properties and the possibil
ity of manufacture on a commercial scale.
Since both the amine and the acid con
tain six carbon atoms in th e molecule, the polymer was identified as polymer “
66
.” ByM olten p o ly m e r is e x tru d e d o n th is c a stin g w heel, called “ M oby D ic k ” b y em - p oyees o f d n F o n t’s n y lo n p la n ts , a n d is sp ra y e d w ith w a te r to so lid ify it
late 1937, a process had been developed for manufacturing interm ediate materials needed in making polymer and a “semi-works”
plant began operating at Belle, W . V a. A pilot plant to produce bristles and textile yam was completed at W ilm ington in the summer of 1938. Commercial manufacture of nylon yarn started at the Seaford, Del., plant in December, 1939, and the second yarn plant w ent into operation at M artins
ville, Va., in November, 1941. T h e original semi-works for making nylon chemicals at Belle, having been increased to a full-scale plant in 1939, is being further augmented by
a
second full-scale plant now under construction near Orange, Tex. Conversion of the chemicals into yarn at th e Seaford plant will be described here.
Five different modifications of polymer
"
66
” are in commercial yam production.They vary in viscosity and in delustrant.
Some are pigm ented, others are bright or non-pigmented.
N Y L O N SALT
T h e Belle plant makes the hexamethylene diammonium adipate, or “salt” as it is more commonly spoken of by the operators. T o facilitate its handling and shipm ent to the yam plants the salt is made into a water solution. O n arrival at Seaford in tank cars, th e solution is pum ped into any one of th e large horizontal storage tanks located out of doors. O ne end of each tank ex
tends into the processing building. Valves, pumps and indicating equipm ent used in connection with the solution are on the in
side of the building where they are pro
tected from the weather. If the tem perature
9 6 M A R C H 1 9 4 6 • CHEMICAL & METALLURGICAL ENGINEERING
rises too high the solution oxidizes and
ous operations associated with the han
dling of any type of yarn. two evaporators, kettles containing tube chests in the bottom , and evaporated at a t
mospheric pressure.
Acetic acid is added to the evaporator charge in order to stabilize the viscosity since any monovalent reactant will interrupt the polymer formation. T h e acid is meas autoclave. Each pair of evaporators serves six autoclaves. T h e autoclaves are jacketed type of polymer desired. Recording instru
C o m m crcial p ro d u c tio n o f n y lo n y a rn obtain best spinning performance the pig
m ent must be very thoroughly dispersed.
As evaporation and elimination of the autoclave is open controls the subsequent operation. A bout an hour is required to ex
and smooth operation requires very close scheduling.
T h e buttons of the storage blenders ex
tend through to the floor below where chutes from them empty into transfer hop
pers operating on a monorail. T h e polymer is conveyed to individual supply hoppers which feed the polymer to' the spinning unit.
Precautions are taken to remove all oxy
gen from the supply hoppers. They are first evacuated and then filled with nitrogen.
T h e nitrogen is of a special purified grade made on the premises and piped into the nylon plant. A portable rotam eter is used to check spinnning machine consumption periodically.
S P IN N IN G
which also serves to blow off th e surface water.
A cutter reduces the polymer ribbon to small chips or flakes. These fall into a portable receiver which is equipped with a screw for blending. Each receiver holds an autoclave charge. Air is drawn through this blender to assist in the drying. A dust collector recovers the small am ount of fine particles.
T h e material in the receiver is sampled and the moisture, viscosity and color is determined. It then goes into a stationary or storage blender in which two or more batches are mixed together by means of a screw device. These blenders are kept tightly sealed since the warm nylon takes up m oisture rapidly from the air. Successful
N ylon y a rn , a f te r th e fin e fila m e n ts e x tru d e d fro m tk e s p in n e re t h av e b een b ro u g h t to g e th e r, is w ound o n b o b b in s
an d sent to tex tile a re a o f th e p la n t
C asting w heel a n d c u tte r a r e in o n e u n it w hich trav els o n th re e ra ils a n d o b ta in s its p o w er f o r o p e ra tio n fr o m a n o v erh ead f o u r th ra il
W h e n the supply hopper has been freed of oxygen and loaded with polymer, the plug cock is opened perm itting the flake to fall by gravity into the spinning unit which is composed of a metal block surrounded by a Dowtherm vapor-heated jacket. This keeps the tem perature of the metal block above the melting point of the material. In this block there is a D owtherm vapor-heated grid. W h en the flake comes in contact w ith the grid it melts and dribbles through to a m elt chamber, which is a small reser
voir below.
From this chamber there are port holes which lead to the gear spinning pumps.
T h e pumps deliver the polymer to a sand filter which is followed by a screen and the spinneret. Throughout these operations air m ust be excluded to avoid oxidation.
Filaments pass down through a cooling chimney. They next pass through a con
verging guide which gathers them into a bundle. T h e bundle continues on its
jour-9 8 • M A R C H 1 9 4 6 • CHEMICAL & METALLURGICAL ENGINEERING
H e re th e n y lo n y a m is sized as it w inds fr o m o n e p a c k a g e to a n o th e r ; a f te r will be more stable toward deformation.
T he yarn is stretched or drawn to the desired degree by running it through a sys
tem of rollers in such a manner th at it is extended to four or more times its original length, depending upon the particular poly
amide being processed. A highly interesting phenomenon occurs during this stretching operation. T h e long, chain-like molecules subsequent manufacturing operations. T he finding of a suitable sizing material proved subsequent aqueous bath processing of the knitted hose. O ne solution to the problem
acting tarnishing conditions. As th e chemi
cals to be handled were new there was no previous experience upon which to base the selection. T h e D u P ont engineers decided to specify the best materials of construction available since even the discoloration product th at would be caused by tarnishing would be considerable knowledge of the corrosion and tarnishing resistance of many metals and percent sulphuric acid solution which hydro
lyzes the nylon to adipic acid and hexa- methylene diammonium sulphate. T h e mix
ture is cooled and the adipic acid crystallized out. T he resultant crystalline slurry is centri
fuged in a rubber-lined centrifuge to remove steel filter press and the acid recrystallized
in glass-lined vessels. T h e effluent from the centrifuge, a solution of hexamethylene dia
mine and sulphuric acid is mixed w ith a lime slurry which neutralizes th e acid.
A precipitated calcium sulphate is formed which is centrifuged off leaving a dilute solu
tion of diamine (7 percent concentration).
time pressure for additional nylon output the recovery process went directly from the laboratory to commercial scale w ithout the customary pilot plant interm ediate stage.
W h ile the foregoing description has had to do principally w ith nylon yarn produc
tion, polymer
66
and other superpolymers arc made for toothbrush and paint brush bristles, surgical sutures, fishing leaders, molded plastics and many other products. pictured flowsheet of nylon production.CHEMICAL & METALLURGICAL ENGINEERING • M A R C H 1 9 4 6 « 9 9