Saturday, October 5, 2019

POLYLACTIDE FIBRE, CHARACTERISTICS OF POLYLACTIDE FIBRE, USES OF POLYLACTIDE FIBRE

POLYLACTIDE( POLYLACTIC ACID) FIBRE:

“A man-made fibre consisting of at least 85% of lactic acid ester units by weight and derived from naturally occurring sugars is known as polylactide fibre”. Since polylactide fibre gets fully decomposed naturally, sothat it is also known as eco-friendly fibre. It is fully biodegradable fibre. It does not harm to our environment. It is a complete replacement of polythene fibres which is today's the biggest problem. Disposal of polythene is very difficult. The recycling of polythene is also limited. The polylactide fibre can replace the polythene sheet to be using in the food packaging industry.

The polylactide is versatile fibre. “Polylactic acid or polylactide is a thermoplastic aliphatic polyester”. It is derived from renewable resources such as corn starch, , tapioca roots, chips or starch or sugarcane. There are two main monomers used to produce polylactic acid or polylactide.  These monomers are lactic acid, and the cyclic di-ester. Polylactic acid is manufactured by using ring-opening polymerization.
”.

PRODUCTION OF POLYLACTIDE:

The manufacturing of polylactide completes in following steps:



Polymerisation:
The polylactide fires are produced by using following method:

Ring opening polymerization:

Ring opening polymerization reaction is most commonly used to produce the polylactide. The polymerization reaction is carried out in the presence of different metal catalysts. 



This reaction is carried out in solution of tin octoate in the melt or suspension. The metal-catalyzed reaction tends to cause racemization of the polylactic acid, reducing its stereoregularity compared to the starting material.

Direct condensation of lactic acid monomer

Another method of producing polylactic acid  is the direct condensation of lactic acid monomers. 


The condensation reaction is carried out at less than temperature 200 °C, because the entropically favoured lactide monomer is formed above that temperature. During  this reaction, “one equivalent of water for every condensation (esterification) step is formed”. This  is not desired because water causes chain-transfer leading to low molecular weight material. Due to above reason, the direct condensation is carried out in different steps. First of all  lactic  acid is oligomerized to polylactic acid oligomers.



After this polycondensation is carried out in the melt or as a solution, “where short oligomeric units are linked to give a high molecular weight polymer strand”. Water generated in during this reaction is  removed by using vacuum  or azeotropic distillation, which is crucial to favour  polycondensation over transesterification. Even higher molecular weights can be attained by carefully crystallizing the crude polymer from the melt. Carboxylic acid and alcohol end groups are thus concentrated in the amorphous region of the solid polymer, and so they can react.


CHARACTERISTICS OF POLYLACTIDE

Polylactide posses following important characteristics:
1 - Polylactide has degree of crystallinity of near about 37%.

2 - The glass transition temperature of polylactide ranges between 60°C - 65 °C.

3 - The polylactide begins to melt at a temperature between 173°C -178 °C.

4 - Heat resistance: polylactide fibre can remain stable at temperatures of 110 °C.

5 - Polylactic acid or polylactide fibre gets dissolved in chlorinated solvents, hot benzene, tetrahydrofuran, and dioxane.

6 - The polylactide is a biodegradable fibre.

7 - It has low moisture regain 0.4 to 0.6 ℅ and high wicking property.

8 - Flammability of polylactic acid or polylactide is low and smoke generation is also very low when it burns.

9 - It has high resistance to ultra violet  radiation.

10 - Due to low refraction index its colours look very rich.

11 - It has low specific gravity 1.25 grams / cc

12 - The  glass transition temperature of polylactic acid ranges between 60°C - 65 °C.

13 - It has a crystallinity near about 37%.

14 - The melting point of polylactide fibre is 173°C -178 °C.

15 - tenacity of polylactide fibre is 32 - 36 cN / tex

USES OF POLYLACTIDE FIBRES:

Polylactide fibre has following many important uses:
Injection molding.

Various types of films.

Sheet casting.

Biodegradable cups.

Tea or coffee  bags are made of polylactide.

It has very significant medical uses(screws,pin,rods and mesh) because it breaks down within the body within six months to two years.

Apparel ,outdoor furniture and furnishings.• Disposable tableware.

Food packaging.

Feminine hygiene products, and diapers.

Upholstery.

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