Dyneema process

Gel-spun polyethylene is produced by DSM in cooperation with Toyobo (Dyneema) and Honeywell, formerly Allied Signal (Spectra). From the relevant patents it is fairly obvious that different solvents are used a volatile solvent in the Dyneema process and a nonvolatile solvent in the Spectra process. 

Fibres are, as a result of the spinning process, molecularly oriented, and they have, therefore, a 2 to 3 times higher stiffness than the non-oriented polymer (e.g. polyamide and polyester textile fibres). With the highest attainable orientation, such as in aromatic polyamides (Twaron and Kevlar), and in the PE-fibre (Dyneema) the stiffness can be a hundred times higher than the one in the unoriented condition ... 

In 4.3 we have already seen that polymers, in the rubber or fluid condition, crystallize much more rapidly when their chains are oriented. Therefore a stretched rubber, if stereospecific in its molecular structure, is able to crystallize at a temperature considerably above its equilibrium thermodynamic melting point. Also a thermoplast such as polyethylene, when in the molten state or in solution, can crystallize spontaneously when the chains are being orientated in elongational flow. The latter case is utilized when polyethylene is spun from a diluted solution (gel spinning process), resulting in fibres of super-high strength and stiffness ( Dyneema fibres). 

Recently elastic polyolefin fibres have also been introduced (generic name lastol), they are cross-linked and stable at temperatures up to 220 °C and above.- High-tenacity polyethylene fibres, with ultra high molecular weight (UHMW-PE, Dyneema) have been available for some time they are produced by a gel-spinning process at high dilution. 

In gel spinning, a variant of solvent spinning, the polymer is fed as a gel instead of a solution. With gel spinning, very high orientation and strength are possible. The most widely known fiber made by this process is Spectra and Dyneema, both made from ultrahigh molecular weight polyethylene. 

In gelspinning of PE-fibers three companies are active today of which Allied is working under a DSM license. Dyneema is a joint venture company of DSM and Toyobo. The table gives the main differences in the processes and the resulting differences in properties of the fibers ... 

The properties of the Dyneema fiber get better when the temperature is lower. This holds especially with strength and creep. The tenacity rises fast and a brittle point has not yet been measured. Creep is also sensitive to temperature (Arrhenius type of dependency), reaching lower figures at lower temperatures. The absolute figure for creep also strongly depends on the process as mentioned before and on the grade of UHMWPE that is used to produce the fibers giving rise to differences in the plateau creep rate of more than one decade. 

Producing a product that contains the Dyneema fiber, usually starts with one of the following processes. 

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