Fluoropolymer processing aids

A PET oligomer isolation method has utilised chloroform extraction in a Parr bomb lined with a Teflon-TFE fluoro-carbon resin [40]. The analytics of fluoropolymer processing aids (combustion analysis, XRF, EUR, 19F NMR, OM) have recently been described [29]. Combustion analysis (Parr Oxygen Bomb Calorimeter) can be used for quantitative analysis... 

Table 8.47 shows the available options for the analysis of polymer processing aids, namely combustion and instrumental methods. The best method is dependent on PPA type, the level to be measured, and the available equipment (see also Section 8.2.1.2). Fluoropolymer processing aid concentrations can be determined by WDXRF configured to measure either fluorine or a tracer, and by EDXRF to analyse a tracer [29]. Calibration curves are required. At present, EDXRF or benchtop XRF units cannot directly measure fluorine. For resin or masterbatch producers who prefer to make on-line XRF measurements of processing aid concentrations (to letdown levels of 50-100 ppm), processing aids that contain a tracer (usually BaS04) are available. The analysis time is less than two minutes. 

Intermaterial competition affects the additive business. For example, if metallocene polyolefins displace PVC markets, then the demand for heat stabilisers and plasticisers might decrease, while the need for products such as fluoropolymer processing aids, antiblocks and slip additives might increase. At present, PVC as the main user of additives is under threat as never before. However, green PVC, containing more environmentally friendly FRs and plasticisers as well as non-heavy-metal stabilisers, is now environmentally acceptable. 

Processing aids, lubricants and antistats Most fluoropolymer processing aids (reduce... 

Solution Next-generation fluoropolymer processing aids that clear melt fracture faster, at lower loadings. 

Since the conditioning time required to clear melt fracture in a blown-film line essentially equals lost bags and lost value, any Improvement is welcome. Thus Ampacet has proposed new fluoropolymer processing aids that clear melt fracture faster than "first-generation" additives. 

As implied above, fluoropolymer processing aids can interact with HALS and reduce their effectiveness. The reaction with HALS and also with polyurethanes and polyamides is thought to involve the vinylidene fluoride comonomer units of the fluoropolymer, resulting in poorer performance and discoloration. Grades of fluoropolymer that do not interact with hindered amine light stabilisers have now been developed. 

It has been claimed that boron nitride allows much faster production rates with metallocene LLDPEs than fluoropolymer process aids. American Ceramics is one supplier. 

Fluoropolymer processing aid concentrates can be analysed by FTIR to within 0.1% within a few min [85]. Letdown processing aid levels can be determined down to approximately 400 to 500 ppm with an accuracy of 50 ppm. It is not envisaged that FTIR will be a suitable means for analysing tracers for ownership (of defective products). Low concentrations are necessary here in order not to upset materials properties and to avoid confusion with the additive package. This rules out many aromatics, S and P compounds. Si-based materials. Cl and Br compounds, elements found in colourants (Ti, Ba, Ca, etc.) as well as other elements (e.g. Zn) and various functional groups (COOH, etc.). 

Using NMR total fluorine in pelletised samples containing fluoropolymer processing aids can be analysed in a few minutes [224]. Table 7.30 shows the main features of NMR. LR-NMR has also been used for the determination of additive content in polyamides [215]. 

Excellent thermal stability for high temperature processing Reduces or eliminates die build-up Lowers apparent melt viscosity For use at very low levels Free-flowing fluoropolymer processing aid Can offer performance and cost advantages... 

PA-FTIR, IR, TLC, NMR, potentiometry and chemiluminescence [486], Analysis of fluoropolymer-based processing aids with a specific ion (F-) analyser can be carried out within 15 min per sample [29]. 

Fluoropolymers have been used as processing aids because small quantities can reduce signih-cantly the overall viscosity and thus facilitate extrusion. Feng et al. [1996] examined the mechanism of viscosity reduction in the capillary flow of HDPE/fluoroelastomer blends. X-ray photoelectron spectroscopy, used to characterize the composition of the extmdates surface, indicated only very small traces of the fluoroelastomer on the extrudate, pointing to the fact that the viscosity reduction is due to adhesive failure between the fluoropolymer layer and HOPE. 

Fluoropolymers (e.g., copolymers of vinylidene fluoride and hexafluoropropylene) and silicone-based (e.g., poly-dimethylsiloxanes) additives are often referred to as processing aids, preventing melt-fracture, for example, the so-called sharkskin. Fluoropolymers are applied in concentrations between 0.01% and 0.1%. 

A technique that has shown potential in eliminating interfacial instability is the use of fluoropolymer-based processing aids. These same additives are used to eliminate melt fracture in blown him extrusion. In one study [46], the incorporation of a processing aid into the skin (outer) layer of a three-layer coextrusion suppressed formation of the instability. 

Processing aids to assist material flow during extrusion or injection molding. The internal and external lubricants are recognized. Internally lubricated resins use oils. Teflon , M0S2, or other materials to give the molded part a lower coefficient of friction. The external lubricant can be a sohd, such as sodium or zinc stearate, a fluoropolymer, or silicone resin or liquid. 

In addition, perfluoroalkyl carboxylic acids (PFCAs) and their derivatives have also been synthesized using the ECF process. Typically, an alkyl carbonyl fluoride (for example C7H15COF) is transformed into the corresponding perfluoroalkyl carbonyl fluoride (for example C7F15COF). The carbonyl fluoride is then reacted to yield esters, amides, or carboxylic acid salts which are have all been commercially produced and used as surfactants [4]. The most widely known is the ammonium salt of perfluorooctanoic acid (C7Fi5COOH-NH3), whose major historical use has been as a processing aid in the manufacture of fluoropolymers [29]. 

Per- and poly-fluorinated ether surfactants are the newest commercially available substances in this rapidly expanding group of fluorinated surfactants [33-35]. For example, the phosphate shown in Fig. 4 is used as a grease repellent for food contact paper [36]. Per- and poly-fluorinated polyether carboxylates [37-41] are also used as processing aids in the synthesis of fluoropolymers. Per- and poly-fluorinated polyether silanes are used as surface treatments [42-45]. 

Fluorinated surfactants have been used for decades as processing aids during aqueous emulsion polymerization synthesis of fluoropolymers such as poly (tetrafluoroethylene). The function of the fluorosurfactant is to solubilize both the fluorinated monomer(s) as well as the growing fluoropolymer. Historically, the... 

PFCA is another important PFC group. The main use of perfluorooctanoate (PFOA) is as a process aid in the manufacture of various fluoropolymers, such as polytetrafluoroethylene (PTFE). These polymers are among other things, used to coat cookware intended for stovetop cooking and baking. 

With ever-increasing competition to reduce costs, process aids are being promoted as cost savers, reducing cycle times and giving substantially defect-free production, while maintaining high output rates and low processing temperatures. Most of the products currently on offer are fluoropolymers, silicones or minerals. Fluoropolymers will be considered first. They are typically used at dose levels of 100 to 1000 ppm. 

The latest Viton FreeFlow additives are among those that have a reduced tendency to interact with other constituents of the formulation. Another new non-reactive fluoropolymer additive has been developed by Dyneon in association with 3M Canada to overcome similar problems, and has been found to perform well in LDPE and LLDPE film. The later versions of Dyneon polymer processing aids act as effective process aids in polyamides and PU, without the usual discoloration and processing problems. 

Dyneon, a wholly owned subsidiary of 3M set up in 1996, is one of the world s leading fluoropolymer producers with operations or representation in more than 50 countries. It sells process aids to the plastics industry, particularly polyolefins. Other products include fluoroelastomers, PTFE and speciality additives for rubbers. Among fluoropolymers, there are additives to prevent dripping in burning plastics. 

Dyneon acquired Solvay Fluoropolymers in 2001, including a PVDF manufacturing facility. In November 2004 it entered into an agreement with SpecialChem SA to moimt a web-based technical service facility for polymer process aids. The company employs more than 800 people worldwide. 

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