Cellulose plasticising

Comparison of Table 5.4 and 5.7 allows the prediction that aromatic oils will be plasticisers for natural rubber, that dibutyl phthalate will plasticise poly(methyl methacrylate), that tritolyl phosphate will plasticise nitrile rubbers, that dibenzyl ether will plasticise poly(vinylidene chloride) and that dimethyl phthalate will plasticise cellulose diacetate. These predictions are found to be correct. What is not predictable is that camphor should be an effective plasticiser for cellulose nitrate. It would seem that this crystalline material, which has to be dispersed into the polymer with the aid of liquids such as ethyl alcohol, is only compatible with the polymer because of some specific interaction between the carbonyl group present in the camphor with some group in the cellulose nitrate. 

Today plasticisers are used in a variety of polymers such as polyvinyl acetate, acrylic polymers, cellulose acetate and, most important of all, poly(vinyl chloride). 

Although originally a trade name the term celluloid has come into general use to describe camphor-plasticised cellulose nitrate compositions. 

Nitration of cellulose followed by plasticisation of the product with camphor has the effect of reducing the orderly close packing of the cellulose molecules. Hence whereas cellulose is insoluble in solvents, except in certain cases where there is chemical reaction, celluloid is soluble in solvents such as acetone and amyl acetate. In addition the camphor present may be dissolved out by chloroform and similar solvents which do not dissolve the cellulose nitrate. 

The solvation by plasticiser also gives celluloid thermoplastic properties owing to the reduction in interchain forces. On the other hand since the cellulose molecule is somewhat rigid the product itself is stiff and does not show rubbery properties at room temperature, cf. plasticised PVC. 

Although acetylation thus renders the cellulosic structure soluble, cellulose acetate will still decompose below its softening point. It is thus necessary to compound cellulose acetate with plasticisers in order to obtain plastics materials of suitable flow properties. Other ingredients are also added at the same time. 

Although the prime function of plasticisers in cellulose acetate is to bring the processing temperature of the compound below the polymer decomposition temperature, it has additional values. An increase in the plasticiser content will reduce the melt viscosity at a given temperature and simplify processing. The physical properties of the finished product will be modified, increasing toughness... 

Although many plasticisers have been suggested for cellulose acetate very few have been used in practice. The most important of these are dimethyl phthalate (8 = 21.4), triacetin (8 = 20.3) and triphenyl phosphate (8 = 20.0), each of which have a solubility parameter within one unit of that of cellulose diacetate (-22.0). (All in units ofMPa. )... 

Triphenyl phosphate is a crystalline solid which has less compatibility with the polymer. This may be expected from solubility parameter data. It is often used in conjunction with dimethyl phthalate and has the added virtues of imparting flame resistance and improved water resistance. It is more permanent than DMP. Triacetin is less important now than at one time since, although it is compatible, it is also highly volatile and lowers the water resistance of the compound. Today it is essential to prepare low-cost compounds to allow cellulose acetate to compete with the synthetic polymers, and plasticisers such as ethyl phthalyl ethyl glycollate, which are superior in some respects, are now rarely used. 

Table 22.4 Influence of amount of plasticiser (dimethyl phthalate) on some physical properties of cellulose acetate compositions...

As a result of development work between the Battelle Institute in Frankfurt and a German candle-making company, Aetema, biodegradable cellulose acetate compounds have been available since 1991 from the Rhone-Poulenc subsidiary Tubize Plastics. They are marketed under the trade names Bioceta and Biocellat. The system is centred round the use of an additive which acts both as a plasticiser and a biodegrading agent, causing the cellulose ester to decompose within 6-24 months. 

The resultant yellow sodium cellulose xanthate is dispersed in an aqueous caustic soda solution, where some hydrolysis occurs. This process is referred to as ripening and the solution as viscose . When the hydrolysis has proceeded sufficiently the solution it transferred to a hopper from which it emerges through a small slit on to a roller immersed in a tank of 10-15% sulphuric acid and 10-20% sodium sulphate at 35-40°C. The viscose is coagulated and by completion of the hydrolysis the cellulose is regenerated. The foil is subsequently washed, bleached, plasticised with ethylene glycol or glycerol and then dried. 

OL Cellulose filled Woodflour filled Plasticised Translucent Cellulose filled Glass filled Mineral filled ... 

In 1991 Rhone-Poulenc offered biodegradable cellulose acetate compounds in which an additive acts both as plasticiser and biodegrading agent (see Section 22.2.2.1). 

Where transparency is required, a range of polymers is available. Polystyrene is the least expensive but polymethylmethacrylate has an outstanding high light transmission combined with excellent weathering properties. Also to be considered are the polycarbonates, glass-clear polyamides, SAN, butadiene-styrene block copolymers, MBS polymers, plasticised PVC, ionomers and cellulose esters such as cellulose acetate. 

With these lacquers, nitrocellulose-based primer-surfacers are used. As well as liquid plasticisers, a wide range of materials are used as plasticising resins short oil alkyds, maleinised oils, ester gum, rosin and bodied castor oils. Pigmentation is usually inert. Thermoplastic acrylics are often preferred under acrylic lacquers these are based on acrylic resins and cellulose acetate butyrate. 

Plasticised amorphous thermoplastics Certain plastics may be mixed with high-boiling low-volatility liquids to give products of lower T. The most important example occurs with p.v.c. which is often mixed with liquids such as di-iso-octyl phthalate, tritolyl phosphate or other diesters to bring the below room temperature. The resultant plasticised p.v.c. is flexible and to some degree quite rubbery. Other commonly plasticised materials are cellulose acetate and cellulose nitrate. 

The TLC process is an off-line process. A number of samples are chromatographed simultaneously, side-by-side. HPTLC is fast (5 min), allows simultaneous separation and can be carried out with the same carrier materials as HPLC. Silica gel and chemically bonded silica gel sorbents are used predominantly in HPTLC other stationary phases are cellulose-based [393]. Separation mechanisms are either NPC (normal-phase chromatography), RPC (reversed-phase chromatography) or IEC (ion-exchange chromatography). RPC on hydrophobic layers is not as widely used in TLC as it is in column chromatography. The resolution capabilities of TLC using silica gel absorbent as compared to C S reversed-phase absorbent have been compared for 18 commercially available plasticisers, and 52 amine and 36 phenolic AOs [394]. 

APCI-MS/MS is not only useful in the analysis of polymers, such as cellulose acetate, but is also of great value in the identification of copolymer substrates, and the various polymer additives such as antioxidants, stabilisers, and plasticisers. 

Concern over the migration of plasticisers from packaging materials has led to various studies, amongst which monitoring levels of various phthalates from coatings of regenerated cellulose film [433] and of acetyl-tributyl citrate (ATBC) from vinylidene chloride/vinyl... 

More than 90% of all plasticisers are used with PVC, the remainder being used with PVDC, cellulose diacetate, poly(vinyl acetate) (PVAC), nylons, urethanes and acrylates. 

The use of plasticisers, with other than PVC applications, is extensive. Many polar rubber sealants or caulking materials are plasticised in order to make them more pliable, e.g., polysulfides, polychloroprene (Neoprene ), nitrile rubber. Esters, similar to those employed with PVC, are used to render cellulose diacetate ("Acetate") overhead projection sheets more flexible. 

Non-drying oil resins are soluble only in Aromatic hydrocarbons. They are used with amino resins for stoving finishes for appliances. Medium resins are used as plasticisers for cellulose nitrate. Along with natural oils several natural occurring and synthetic acid like resin (abiotic acid) pelargonic acid and isooctanoic acid are added to modify alkye resins. The alkyd resins are obtained by two processes, i.e., (1) Fatty Acid Process and (2) Alcoholysis process. 

During roller-blending to disperse iron red pigment (iron(III) oxide) into plasticised cellulose nitrate, the mixture became a gel after 15 passes and tended to self-ignite. 

TG-MS is an ideal technique for identifying residual volatiles in polymers. The detection of residual volatiles (and of other impurities) can often yield clues as to manufacturing processes. In many cases, such as in the determination of highly volatile materials, of residual solvents or plasticisers, use of TG-MS is requested. Specifically, there are reports on the entrapment of curing volatiles in bismaleimide laminates [145] and elastomers [48], on the detection of a curing agent (dicumylperoxide) in EPDM rubbers and of bromine flame retardants in electronic waste [50], of plasticisers such as bambuterol hydrochloride [142] or TPP and diethylterephthalate in cellulose acetate [143], on solvent extraction and formaldehyde loss in phenolic resins [164], and on the evolution of toxic compounds from PVC and polyurethane foams [146]. 

Cellulose nitrate is a semi-synthetic plastic based on cellulose from wood or cotton. It is mixed with nitric and sulphuric acids, and uses camphor as a plasticiser. It is another compound that was being developed by various people in different places at the same time, but was launched in England in 1862 as Parkesine . It was later called Xylonite . Cellulose nitrate was finally patented in America in 1870 under the name celluloid , but has been known by over 60 different trade names during the years it has been in production. 

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