Melting cellulosics

Ruminococcus albus strain 7, (1), was grown on cellulose roll tubes according to the Hungate technique (2). Either Avicel (FMC Corporation, Marcus Hook, Pa.) or balled filter paper was used as the cellulose source. Three milliliters of melted cellulose-medium at 45 °C. in 16 X 150 mm. tubes were inoculated with the bacteria under a gas phase of 95% C02 and 5% H2. The tubes were subsequently stoppered and rolled in a tray of ice in order to form a film of agar medium around the... 

Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding. 

EthylceUulose [9004-57-3], a cellulose either (qv), as prepared commercially, ie, of high DS, is thermoplastic and has alow density (1.14 g/cm ). It forms films of good thermostabiUty and excellent flexibiUty and toughness. EthylceUulose is used in lacquers, inks, and adhesives and is combined with waxes and resins in the preparation of hot-melt plastics. It is also used as a pharmaceutical tablet binder. 

Many cellulose derivatives form Hquid crystalline phases, both in solution (lyotropic mesophases) and in the melt (thermotropic mesophases). The first report (96) showed that aqueous solutions of 30% hydroxypropylceUulose [9004-64-2] (HPC) form lyotropic mesophases that display iridescent colors characteristic of the chiral nematic (cholesteric) state. The field has grown rapidly and has been reviewed from different perspectives (97—101). 

Fig. 3. Effects of composition on physical properties. A, acetyl B, butyryl C, cellulose. 1, increased tensile strength, stiffness 2, decreased moisture sorption 3, increased melting point 4, increased plasticizer compatibiUty 5, increased solubiUties in polar solvents 6, increased solubiUties in nonpolar...

Cellulose triacetate [9012-09-3] has the highest melting point (ca 300°C) of the triesters melting points generally decrease to a minimum of ca 230°C as the acetyl content decreases to 38—39% (secondary acetate). 

Fig. 10. Differential scanning calorimetry of cellulose triacetate. Second heating at 20°C/min. glass-transition (T temperature = 177 " C crystallization on heating (T)/j) = 217 C melting temperature (Ta) = 289 C. To convert to cal, divide by 4.184.

Determination of the thermal decomposition temperature by thermal gravimetric analysis (tga) defines the upper limits of processing. The tga for cellulose triacetate is shown in Figure 11. Comparing the melt temperature (289°C) from the dsc in Figure 10 to the onset of decomposition in Figure 11 defines the processing temperature window at which the material can successfully be melt extmded or blended. 

Low viscosity cellulose propionate butyrate esters containing 3—5% butyryl, 40—50% propionyl, and 2—3% hydroxyl groups have excellent compatibihty with oil-modified alkyd resins (qv) and are used in wood furniture coatings (155). Acetate butyrate esters have been used in such varied apphcations as hot-melt adhesive formulations (156), electrostatically spray-coated powders for fusible, non-cratering coatings on metal surfaces (157—159), contact lenses (qv) with improved oxygen permeabiUty and excellent wear characteristics (160—162), and as reverse-osmosis membranes for desalination of water (163). 

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

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... 

Steam-heated aluminum castings are used for the melt spinning of nylon and polyester fibers and have been used for storage of raw materials during manufacturing, as well as for storage of acetic acid in cellulose acetate plants. 

Meanwhile, cellulose acetates were intensively studied to produce triacetate, a waterproof varnish to the fabric on World War I airplane wings. Triacetate also was made in powdered (omi for later melting and molding. With manufacturing development of methylene chloride, triacetate film came into use as a photographic base in 1935. Transparent acetate film was developed, and used for packaging. 

Figure 21 DSC melting curves at atmospheric pressure for PE-ethyl cellulose mixture crystallized at elevated pressure. (a) 100 MPa (b) 150 MPa (c) 300 MPa (d) 400 MPa and (e) 750 MPa. (From Ref. 117.)...

A result different from that of Nakafuku et al. [144-147] was obtained by us from the study of a binary mixture of PE-ethyl cellulose liquid crystal under high pressure. We have reported [104,117] that addition of 1% ethyl cellulose by weight facilitates the formation of ECC of PE and moderates the conditions for the formation of ECC, that is, the pressure limit is lowered from 440 MPa to 150-200 MPa, and the temperature limit lowered from 200-245°C to 170°C. The DSC melting curves at atmospheric pressure for pure PE (Mt, = 1.06 x 10, p = 0.9556 g/cm ) and PE-ethyl cellulose mixture crystallized at various pressures are shown in Figs. 20 and... 

Electric discharge methods are known [31] to be very effective for nonactive polymer substrates such as polystyrene, polyethylene, polypropylene, etc. They are successfully used for cellulose-fiber modification to decrease the melt viscosity of cellulose-polyethylene composites [32] and to improve the mechanical properties of cellulose-polypropylene composites [28]. 

This extensive hydrogen bonding bears on several aspects of the chemistry and applications of cellulose. For instance, being a semi-crystalline polymer, cellulose cannot be processed by the techniques most frequently employed for synthetic polymers, namely, injection molding and extrusion from the melt. The reason is that its presumably lies above the temperature of its thermal... 

Cellulose is a linear polymer. Despite this, it is not thermoplastic, essentially because of its extensive intermolecular hydrogen bonding which never allows the molecules to move sufficiently for the polymer to melt. 

These opposing tendencies may defeat the purpose of the fractional precipitation process. The fractional precipitation of crystalline polymers such as nitrocellulose, cellulose acetate, high-melting polyamides, and polyvinylidene chloride consequently is notoriously inefficient, unless conditions are so chosen as to avoid the separation of the polymer in semicrystalline form. Intermediate fractions removed in the course of fractional precipitation may even exceed in molecular weight those removed earlier. Separation by fractional extraction should be more appropriate for crystalline polymers inasmuch as both equilibrium solubility and rate of solution favor dissolution of the components of lowest molecular weight remaining in the sample. 

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