Chemical Product Technology by Dmitry Yu. Murzin

Chemical Product Technology by Dmitry Yu. Murzin

Author:Dmitry Yu. Murzin
Language: eng
Format: epub, pdf
Publisher: Walter de Gruyter
Published: 2018-06-15T00:00:00+00:00


Gelation properties, defined through either processing temperature to which the plasticizer and polymer must be heated or as a solution temperature, at which a polymer grain is dissolved in plasticizer excess, are related to plasticizer polarity and molecular size. Higher polarity translates into a larger attraction for PVC polymer chain and thus lower temperature at which elongation properties can be achieved. Plasticizer polarity depends on the acid type and alcohol chain length with for example more polar aromatic acids being more prone to gelation than aliphatic acid esters. Smaller plasticizers can easier penetrate the PVC matrix requiring less thermal energy for desired interactions with the polymer. Branching is preferential for gelation.

Plasticizer can be extracted from PVC by solvents, including water, at different rate depending on their molecular size and compatibility with the plasticizer and PVC. As can be expected water is not efficient, while low molecular mass solvents are the most aggressive. Extraction resistance depends on the molecular size of the plasticizer and branching, namely larger size and more branching make migration and extraction of plasticizers more difficult.

Plasticizers not only modify physical properties of polymers but also improve processing characteristics. Plastic products are prepared by shaping molten plastic followed by cooling. Hot compounding (e.g. calendering, extrusion, injection and compression molding described in Chapter 2) can be significantly influenced by the plasticizer type and concentration. Lower viscosity, easier filler incorporation and dispersion give lower power demand and processing temperatures. Plasticizers can reduce the second order transition temperature and the elasticity modulus improving cold flexibility.

The extensive use of polymers in such applications as short-term packaging, food and pharmaceutical industries, ignited an interest in biodegradable plasticizers and in plasticizers for natural polymers. Plasticizers for biopolymers should preferably also be biodegradable.

One of the most well-known biodegradable polymer is polylactic acid (PLA), which is brittle, has relatively poor impact strength and low thermal degradation temperature. In addition to these deficiencies a lack of reactive functional groups and high costs limit applications of poly(lactic acid). Low molecular weight compounds such as oligomeric lactic acid, glycerol, triacetin, and low molecular mass citrates can be used as plasticizers of PLA.

Another interesting natural polymer is starch, which during the thermoplastic processing, is transformed from a semi-crystalline into a homogeneous material with hydrogen bond cleavage between starch molecules disrupting long range crystalline structure. Plasticizers penetrating starch and destroying the hydrogen bonds, replace starch–starch interactions by starch–plasticizer interactions. The plasticized moldable thermoplastic starch, used for injection, extrusion or blow molding similar to other synthetic thermoplastic polymers, can be processed with different polyols (glycols of different carbon length, glycerol, xylitol, sorbitol), sugars (fructose, mannose, sucrose) or fatty acids as plasticizers.

Cellulose being an abundant, renewable, and biodegradable natural polymer, constituting the skeletal part of plants, has been for a long time very attractive as a source of industrial materials because of its abundance, costs, environmental benefits and biocompatibility. Cellulose (a crystalline polymer of D-glucose) is poorly soluble in common solvents and cannot be processed in a melt decomposing before. Therefore, derivatives of cellulose



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