/ep_edm/en/contect_246.html SHINI PLASTICS TECHNOLOGIES, INC.

Special Reports

2010 Quarter 3 Issue 4

Brief Introduction to PLA

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PLA Introduction

PLA is abbreviation of biodegradable plastic polylactic acid, and its full name is Polylactic acid.

 

Polylactic acid is also called polylactide which belongs to polyester family. Polylactic acid is a kind of polymer that polymerized from lactic acid and other materials such as corn and tapioca which are ample and renewable. Production process of polylactic acid is free from pollution and the product is biodegradable. It realizes cycle in nature and is green polymer material.

 

 

Drying of PLA

Drying process is not optional with PLA; it is absolutely essential. PLA is a hygroscopic thermoplastic. That is, it readily absorbs moisture from the atmosphere. The presence of even small amounts of moisture will hydrolyze PLA in the melt phase, reducing the melt fluidity and crystallization rate. As a result, the mechanical properties of PLA decrease and the end-product quality is compromised. Therefore, PLA must be thoroughly dry just prior to melt processing. In many cases, recycled PLA may also have to be crystallized prior to drying.

 

Amorphous PLA requires drying at much lower temperatures 43~55℃ with low dew-point (-40℃), to prevent sticking in the dryer.

 

The crystallized PLA should be dried at 65~90℃ (with a dew point of -40℃). Higher drying temperature can lead to softening and blocking of polymer in the dryer. Lower drying temperatures will result in extended drying times.

 

Dryness of the PLA must be maintained until it enters processing equipment. It is best to use dried material right away so it does not absorb ambient moisture. Depending on ambient conditions, dried PLA that is not kept in a sealed enclosure can pick up enough moisture in five minutes to defeat most of the benefits of drying.

 

Virgin PLA is crystallized and dried to 400PPM moisture level prior to leaving the production plant. If the PLA is received in undamaged pakages, the drying requirements are minimal. In addition, if the foil liner has been opened, drying will be required. The resin is crystallized to allow easier drying. Uncrystallized PLA becomes sticky and clumps when its temperature reaches 60℃(1400F). This is PLAs vitrification temperature; the point at which the amorphous portion begins to soften.

 

Selection of Drying Equipment

As mentioned above, PLA should be dried at much lower temperature (65~90℃ for crystallized PLA, and 43~55℃for amorphous PLA) with low dew-point (-40℃).

 

The current SCD series of Shini adopt double-cooler structure in dry air loop which provides dry air with dew point of -40℃. The range of controllable temperature is 55~160℃ and can effectively dry crystallized PLA. Based on standard SCD, an additional cooler is installed at dry air outlet of the honeycomb rotor to dry amorphous PLA. Temperature at air outlet is below 40℃for the purpose of controlling temperature accurately. This series also equip feeding device and suction box with shut-off valve for prompt use of materials. The conveying pipeline is purged thoroughly to prevent materials from absorbing ambient moisture.

 

Shini SCAD-U-HD (equip with heatless air dryer) can also dry amorphous PLA. The dew-point reaches -40℃ and the range of controllable temperature is 50~160℃.Shini presently provides SCAD-1U-HD, SCAD-3U-HD and SCAD-6U-HD.

 

Application of PLA

Production technology for common plastics can be applied for manufacturing PLA products. Various products have been developed in terms of its properties such as food packaging, film, IC packaging, toy, fiber and rope etc.