Processing of the Nylons

The above comments refer to comparisons between the two compositions at the same glass-fibre level. If, however, comparison is made between a nylon 66 composition with a glass content of x% and a nylon 6 compound with a glass content of (x + 5)%, then the differences in mechanical properties become very small. At the same time the nylon 6 material will have slightly easier processing characteristics and surface quality. 

Whilst nylon 66 has the higher T , the long-term heat resistance of typical copper-stabihsed nylon 6 is somewhat superior in such properties as impact strength and bending strength compared to nylon 66. However, it is frequently the case that nylon 66 has better resistance to chemicals at elevated temperatures. 

In the processing of nylons consideration should be given to the following points  

The above features are particularly marked with nylons 46, 6,66 and 610 and less marked with nylons 11 and 12. Providing they are dry the copolymers may be processed in much the same way as conventional thermoplastics. 

Injection moulding cylinders should be free from dead spots and a temperature gradient along the cylinder is desirable. 

When dimensional accuracy is required in a specific application the effect of water absorption should also be considered. Manufacturers commonly supply data on their products showing how the dimensions change with the ambient humidity. 

The particular features of the nylons should also be taken into account in extrusion. Dry granules must be used unless a devolatilising extruder is employed. Because of the sharp melting point it is found appropriate to use a screw with a very short compression zone. Polymers of the lowest melt viscosity are to be avoided since they are difficult to handle. Provision should be made to initiate cooling immediately the extrudate leaves the die. 

---

Nylon. The high degree of crystallinity in nylon means that plasticization can occur only at very low levels. Plasticizers are used in nylon but are usually sulfonamide-based since these are generally more compatible than phthalates. These plasticizers help improve the processing of the nylon. 

A rack and frame press uses heavy nylon cloth positioned in a wooden frame inside a rack. A measured amount of apple or other fmit mash is added from a hopper above the frame. The mash is leveled with a hand trowel and the edges of the nylon cloth are folded over the mash to encase it and create a cheese. The frame is removed, and a second rack is placed on top of the first cheese the process is repeated until a stack of cheeses is prepared. A hydrauhc ram then appHes gradually increa sing pressure on the stack and expresses the juice. A high yield of juice (80%) is obtained and no press aid is required. Because this process is labor intensive (17), it is mostly used for small farm and pilot-plant operations. 

The properties of the nylons are considerably affected by the amount of crystallisation. Whereas in some polymers, e.g. the polyacetals and PCTFE, processing conditions have only a minor influence on crystallinity, in the case of the nylons the crystallinity of a given polymer may vary by as much as 40%. Thus a moulding of nylon 6, slowly cooled and subsequently annealed, may be 50-60% crystalline, while rapidly cooled thin-wall mouldings may be only 10% crystalline. 

Disclosed is a process for recovering monomeric units of a nylon from whole carpet composed of fibres of the nylon and a backing composed of non-nylon components, the fibres being bound to the backing and the carpet containing between 15 and 35 wt.% of the nylon. It involves the steps of a) mechanically separating the whole carpet into a carpet mixture, which contains between 35 and 55 wt.% of nylon, and a depleted carpet mixture, and exposing the carpet mixture to conditions under which depolymerisation of the nylon is effected. 

Prodnction of Nylon-6 from caprolactam is an important global industrial process. Of the several billions of pounds of caprolactam produced armually, most is polymerized to Nylon-6 [1]. Nylon-6 polymer is used in the manufacture of carpets, automotive parts and sporting goods as well as in films and packaging. 

A Nylon recycle based on depolymerization via ammonolysis has been shown to be a technically feasible route for the recovery of high purity Nylon intermediates (1-6). In the ammonolysis process, the secondary amides of the Nylon (-6 and / or -6,6) fibers/polymers react with ammonia to break the Nylon chain and form a primary amide and an amine (Figure 1). The primary amide can subsequently be dehydrated to form a nitrile group. The net result is that the ammonolysis product is predominantly a mixture of four major components. 

Since the hydrogenation step of the Nylon ammonolysis process had not been studied extensively, it was deemed necessary to investigate the feasibility of a relatively low-pressure (less than 1000 psig) and low-temperature (less than 100°C) process for the hydrogenation of depolymerized Nylon-6,6 and/or a blend of Nylon-6 and -6,6 products. 

Nylon (polyamide fibers). The chemical structure of the nylon fiber looks just like the nylon resin. The polymerization processes are the same the numbering systems are the same and the two most important nylon fibers are the same nylon, 6 and 66. The difference is the length of the molecule in comparison to the cross-section. Thats regulated by the polymerization process conditions. 

The production of the nylon precursor e-caprolactam via the Beckmann rearrangement is one of the largest industrial processes worldwide. There are a large number of synthetic routes to e-caprolactam, most of which need to be improved because, without exception, all are multistage processes that produce large amounts of by-products, primarily ammonium sulfate. Due to its industrial application, the improvement of the Beckmann rearrangement of e-caprolactam was the aim of several smdies and a lot of scientific papers, patents and book chapters have been published on this topic during the last century. 

The immobilization process, however, can be complicated. The immobilization of an enzyme on nylon serves as a point of comparison. The first step is to activate the surface of the nylon by treating it with hydrochloric acid at room temperature for 24 hours. The partially hydrolyzed nylon is then dried in ether and stored in a desiccator overnight. The nylon is then mixed with a coupling agent [l-ethyl-3-(3-dimethyaminopropyl)] and shaken for 1 hour. The enzyme is then added and shaken overnight at 4 C. 

In previous work, a model skin-core composite fiber with a nylon core and a rayon skin was produced by a coating process fl, 2], The composite fibers exhibited the mechanical properties of the nylon core, while the moisture regain was proportional to the thickness of the rayon skin. 

Nylons. Figure 11 shows two small, single nylon fiber samples run by TMA. Despite the small size, all the major characteristics could be evaluated the dehydration contraction, the glass transitions, the processing temperatures and the melt. These two similar samples of nylon displayed similar qualitative behavior characteristic of the nylons, and from the temperatures of the transitions it is clear that Nylon 6 and Nylon 6-6 can be easily distinguished by their melting curves using TMA. 

As one step in the process of making nylon, dichlorobutene (DCB) is reacted with sodium cyanide to form dicyanobutene (DNB). A CSTR is used to carry out the reaction and special controls and materials of construction are required. 

The tensile properties of isotactic polypropylene materials reinforced with continuous nylon fibers were measured. Less than 10 vol % of the fibers leads to an increased yield strength and yield elongation. As little as 3 vol % of the nylon fibers increased the elongation at necking from 10 to 20%. This retarded necking arises from the fiber-matrix debonding which delocalizes the microscopic yielding processes. 

---