Multilayered inhibiting films

Extrusion by pol3Tner hose blowing may produce both single-layer and multilayered inhibited films. It is highly productive, quiet simple and facilitates regulation of dimensions, structure, physical-mechanical and other characteristics of the film materials within a wide range. 

Multilayered inhibited films with Cl desorption on one of the sides can be produced by a process illustrated in Fig. 2.5e, in which the liquid forced into the hose cavity is a film-forming inhibiting composition. To manufacture adhesive Aims on a polyolefine base, a film-forming composition has been developed that contains 2-10 wt% of mineral oil, 4-12 wt% of oil-soluble Cl, 3-10 wt% of rubber, 3-10 wt% of rosin, 5-16 wt% of tall pitch in an organic solvent. The composition is brought into contact with the extruded hose at a temperature of T = (0.6-0.9) Tm of polyolefine. As a result, an adhesive coating is formed on the hose surface, which is the source of Cl and shows high adhesion to metals (about lON/cm ) and to the base Aim [80]. 

An original design for the extrusion head has been developed for manufacture of multilayered inhibited film materials with a fibrous melt-blown polymer layer (B) bonded to the inner or outer surface of the film base (F), and the materials of the F-B-F-B-F structure [81]. A peculiarity of this... 

Fig. 2.12. Structure of multilayered inhibiting films (a) two-layered and (b) threelayered film composed of two polymer materials A and B, (c) three-layered film made of three materials A, B and C (1) and (4) solid layers, 2 and (3) Cl-filled areas of layers B and C...

The method of casting solutions and polymer latexes, as well as application of polymer plastisols containing Cl on the forming substrate is used for the manufacture of both single-layer and multilayered inhibited films [3,4,23,25,41,43,53,84] as well as films with an adhesive layer [57,58]. 

Certain structural schemes of multilayered inhibited films in which Cl carrier is e.g. a varnish coat (Fig. 2.10) or individual layers (Fig. 2.12) have been considered earlier in Sect. 2.2 and 2.1 (Fig. 2.3). 

According to their structural parameters the inhibited films are subdivided into single-layer and multilayered, when a few layers of one or different polymers are formed, and combined films that contain other materials along with the polymer film layers. 

In addition, process schemes for manufacturing laminated inhibited films by co-extrusion are presented in Fig. 2.11. Working volumes of extruders 1 for processing polymer materials (A, B, C) are connected with extrusion head body 2. The head is fitted with several annular slots that form, on blowing, a multilayered hose 3. Two-ply films can be formed from the same [7] or two different (Fig. 2.11a) polymers. Three-layered films can, correspondingly, incorporate two (Fig. 2.11b) or three different (Fig. 2.11c) polymer materials. 

Single-layer inhibited films can neither present a insurmountable barrier to diffusive permeation of corrosion-active agents from the outside, nor they can avert infiltration and condensation of water vapor on the metal surface, but are able to hamper the removal of ion products from the zone of electrochemical reactions. The corrosion protection barrier factor is drastically improved in multilayered film materials. 

The vast majority of corrosion inhibitors in neutral environment as well as a number of acid corrosion inhibitors form protective 3D films on the metal surface ( interphase inhibition [4]). These films may consist of adsorbate multilayers, ox-ide/hydroxides, salts, or reaction products formed by interaction of the inhibitor with solution species on or near the corroding metal surface (e.g. dissolved metal ions). The type, structure, and thickness of the inhibiting films are strongly influenced by the environmental conditions. The interphase films act as a physical barrier that blocks or retards transport processes and the kinetics of the corrosion reactions at the metal surface. The inhibitive properties could, in some cases, be correlated with the chemical stability of the corresponding insoluble complexes as well as with the solubihty, adsorbabOity, and hydrophobicity of the inhibitor molecules [35]. Often, other ions from the electrolyte, such as... 

Catalysis at multilayered electrode coatings is then addressed. Besides the rate of the catalytic reaction within the film and the diffusion of the substrate and products between the bulk of the bathing solution and the film-solution interface, the current response depends on two additional factors permeation of the substrate through the film, and transport of electrons through the film. Analysis of the first of these factors also involves a discussion of the inhibition of the electrode electron transfer that the presence of a film on the electrode surface may cause, whether the electrode is covered by a monolayer or by a thicker film. This discussion also addresses the important case where inhibition is due to deposition onto the electrode surface of one of the reaction products. 

In contrast, the adsorbed layer in protein-stabilized thin films is much stiffer and often has viscoelastic properties [3]. These derive from the protein-protein interactions that form in the adsorbed layer (Figure 1(b)). These interactions result in die formation of a gel-like adsorbed layer in which lateral diffusion of molecules in the adsorbed layer is inhibited. Multilayer formation can also occur. This serves to further mechanically strengthen the adsorbed layer. 

Alternatively, the container may contain an opacifying agent, e.g., titanium dioxide. The use of multilayered bags was demonstrated to inhibit photochemical decomposition of vitamin E in TPN fat emulsions (Allwood and Martin, 2000). PVC films discolor on irradiative exposure due to photochemical degradation of the polymer (Hollande and Laurent, 1997). Plastic containers for parenteral use may contain several additives, e.g., antioxidants, stabilizers, plasticizers, lubricants, impact modifiers, and coloring matter when justified and authorized. In an appendix, the European Pharmacopoeia presents a list of plastic additives that may be used (European Pharmacopoeia, 2002). The additives should not be extracted by the contents in such quantities as to alter efficacy or stability of the product or to present any risk of toxicity (European Pharmacopoeia, 2002). However, organic additives extracted in concentrations below the detection limits of the analytical methods authorized by the European Pharmacopoeia may be sufficient to initiate photosensitized reactions in the formulation. 

This class of inhibited plastics includes multilayered films containing particles of a powder inhibitor between its polymer layers. 

Polyolefine films are the most applicable, in which the high-density polymer layers fulfil the strengthening and barrier functions and a layer of low-density polyolefine contains a Cl [19,28,30]. For instance, in a strengthened multilayer Cortec VCI-126 film the outer layer is formed of LDPE with HOPE strips. The inner inhibited layer is made of LDPE. 

The simplest modifications of named materials are multilayered and combined films in which either solid [41] or porous polymer layers (foamed, fibrous, etc.) are filled with the inhibiting liquid [4,18,23,24,30,39]. In addition, film materials where the adhesive layer is filled by a liquid Cl are used in packaging techniques [4,23,37]. 

Multilayered and combined inhibited hose films are mainly produced by co-extrusion methods. Apart from these, original procedures for obtaining adherence to the hose base functional layers (coats) are employed. In one of these [50] a barrier coating is formed on the outer surface of the hose film filled by Cl using one of aforementioned methods. 

Fig. 7 High-resolution in situ STM images showing the structure of inhibiting BTAH films on Cu(lOO) at different BTAH coverages, (a) Chainlike structures at submonolayer coverages (350 A X 350 A) (b) close-packed arrangement in the completed chemisorbed BTAH monolayer (100 A X 100 A) (c) model of the BTAH adsorption geometry in the close-packed monolayer phase [rectangles in (d) and (c) indicate the surface unit cell of the BTAH adlayer] and (d) disordered polymeric chains in the Cu(l)BTA multilayer phase (300 A x 300 A) [22, 24, 25).

Unoriented Films. Unoriented multilayer films can be obtained by coextrusion of layers of 3GN and PET. Alternatively, multilayer films can be formed in a continuous lamination process using heat or optionally adhesive layers to bond the separate layers. Press lamination can also be used to form multilayer films by pressing layers of individual films at elevated temperature and pressure. Prior to film formation, the pol5miers are generally dried by heating to a temperature of 5°C below the crystallization temperature of the polymer under vacuum or inert atmosphere. The films can be rapidly cooled after extrusion to inhibit crystallization. ... 

Figure 11.13 Examples of constrained sintering (a) a composite in which inclusions prevent the powder matrix form sintering freely (b) an adherent thin film for which sintering in the plane of the film is inhibited by the substrate (c) a multilayer in which the layers sinter at different rates.

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