Addition of Plasticizers

Plastics and Resins. Plastics and resin materials are high molecular weight polymers which at some stage in their manufacture can be shaped or otherwise processed by appHcation of heat and pressure. Some 40—50 basic types of plastics and resins are available commercially, but HteraHy thousands of different mixtures (compounds) are made by the addition of plasticizers, fillers, extenders, stabilizers, coloring agents, etc. 

The amount of plasticizer added to the polymer in question varies, depending on the magnitude of the effect required. For example, a small addition of plasticizer may be made simply to improve the workabiUty of the polymer melt. This contrasts with larger additions made with the specific intention of completely transforming the properties of the product. For example, PVC without a plasticizer, ie, unplasticized PVC (PVC-U), is used in appHcations such as pipes and window profiles with plasticizer added, articles such as PVC food film, PVC cable insulation, and sheathing and PVC floorings are formed. 

Phosphate Esters. The principal advantage of phosphate esters is the improved fire retardancy relative to phthalates. The fire performance of PVC itself, relative to other polymeric materials, is very good due to its high halogen content, but the addition of plasticizers reduces this. Consequendy there is a need, in certain demanding appHcations, to improve the fire-retardant behavior of dexible PVC. 

Polyolefins. Interest has been shown in the plasticization of polyolefins (5) but plasticizer use generally results in a reduction of physical properties (12), and compatibiHty can be achieved only up to 2 wt %. Most polyolefins give adequate physical properties without plasticization. There has been use of plasticizers with polypropylene to improve its elongation at break (7) although the addition of plasticizer can lower T, room temperature strength, and flow temperature. This can be overcome by simultaneous plasticization (ca 15 wt % level) and cross-linking. Plasticizers used include DOA. 

Tensile elongation of PVA is extremely sensitive to humidity and ranges from < 10% when completely dry to 300—400% at 80% rh. Addition of plasticizer can double these values. Elongation is independent of degree of hydrolysis but proportional to the molecular weight. Teat strength increases with increasing relative humidity or with the addition of small amounts of plasticizer. 

Adhesives. Poly(vinyl alcohol) is used as a component in a wide variety of general-purpose adhesives to bond ceUulosic materials, such as paper and paperboard, wood textiles, some metal foils, and porous ceramic surfaces, to each other. It is also an effective binder for pigments and other finely divided powders. Both fully and partially hydrolyzed grades are used. Sensitivity to water increases with decreasing degree of hydrolysis and the addition of plasticizer. Poly(vinyl alcohol) in many appHcations is employed as an additive to other polymer systems to improve the cohesive strength, film flexibiUty, moisture resistance, and other properties. It is incorporated into a wide variety of adhesives through its use as a protective coUoid in emulsion p olymerization. 

Vinyl chloride polymers are produced in two main types, homopolymers and copolymers, usually with vinyl acetate. Both types can be plasticized by a wide variety of plasticizers (qv), usually esters. Rigid or unplasticized PVC is used extensively for pipe. The plasticized material is used largely in floor coverings. The homopolymer itself is inherently fire-resistant, but addition of plasticizers, unless they are especially fire-resistant, considerably reduces this characteristic (see Elame retardants). 

Plasticizers. Addition of plasticizers (qv) to polyether elastomers alters physical properties, improves processing, and can improve low temperature flexibiUty. Plasticizers also reduce vulcanizate costs by allowing the use of higher levels of less expensive fillers. 

Joining of finished plastic components by fusing materials either with or without the addition of plastic from another source. 

Brauer, Stansbury Flowers (1986) modified these cements in several ways. The addition of various adds - acetic, propionic, benzoic etc. -accelerated the set. The use of zinc oxide powders coated with propionic add improved mixing, accelerated set, reduced brittleness and increased compressive strength from 63 to a maximum of 72 MPa. The addition of plasticizing agents such as zinc undecenylate yielded flexible materials. Incorporation of metal powders had a deleterious effect and greatly increased the brittleness of these cements. The addition of fluorides was not very successful, for fluoride release was not sustained. 

PVC is flexibilized by addition of plasticizers as already noted. It is also made more flexible through blending with elastomers that act as impact modifiers. These blends are used when impact resistance is essential. 

Although some polymers may be satisfactory when used under the stress of static loads, they may fail when subjected to impact. The impact resistance, or resistance to brittle fracture, is a function of the molecular weight of a polymer. Thus uhmwpe is much more resistant to impact failure than general purpose high-density polyethylene (hdpe). The impact resistance of brittle polymers is also increased by the addition of plasticizers. Thus polyvinyl chloride (PVC), plasticized by relatively large amounts of dioctyl phthalate, is much less brittle than unplasticized rigid PVC. 

A qualitative relationship exists between the electric and mechanical relaxation times. Both are increased by the addition of fillers and reduced by the addition of plasticizers. 

Sometimes, addition of plasticizer imparts flame retardant characteristics in addition to other properties. Phosphate esters such as tris(2-ethyl hexyl) phosphate (TOP), tricresyl phosphate (TCP), chlorinated paraffin hydrocarbons etc. impart excellent flame retardant characteristics to many polymers. 

In Fig. II the effect of plasticizer is shown for the system poly(vinyl chloride)/tricresyl phosphate. Water also affects the conductivity considerably but its precise function is by no means clear particularly at low moisture contents (135). The presence of ionic impurities causes increased conductivity but the effect of organic impurities is less apparent. For instance, the addition of plasticizers of differing purity to poly-... 

The results obtained by addition of plasticizer vary with different polymers. In polyvinyl chloride, for example, plasticizer concentrations of 30 50% convert the hard, rigid resin to rubber-like products having remarkably high elastic recovery, while similar plasticizer concentrations in cellulose acetate produce tough but essentially rigid products. 

The analyte sensitivity and response time of a PVC film can also be markedly improved with addition of plasticizers such as tributyl phosphate (TBP) or tripropyl phosphate (TPP), since it is well established that the presence of plasticizer in the polymer-encapsulating medium increases gas diffusion rate by increasing the degree of polymer segmental mobility. It is... 

Additional plasticizer was added and hand stirred until a smooth paste resulted. (In general, the pastes were highly dilatent. The addition of plasticizer was halted when a shiny texture was noticed.)... 

The addition of plasticizer disrupts the hydrogen bonding in the system and, hence, the physical properties decrease. To overcome this, at low harnesses, some long-chained material can also be added. A simple system is shown in Figure 5.3, where some additional plasticizer such as DIOP is added to a 95 Shore A polyether prepolymer, which has been cured with Ethacure 300. 

The hardness of polyurethanes can be obtained by either the density of the hard segments, the choice of curative, or the addition of plasticizer. The importance of hardness is to control the rigidity of the part (if not reinforced) or its softness to conform to the shape of some other object it passes over. For very low hardness (< 60 A) applications such as rolls, TDI esters are the most suited, whereas ether-based materials are least suited. Hard materials do have better abrasive resistance than soft materials. 

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