POLYLACTIC ACID BLOWN FILM AND METHOD OF MANUFACTURING SAME
The invention provides polylactic acid (PLA) films substantially free of plasticizers and methods of manufacturing same by blown film process are provided. PLA films are environmentally degradable and have applications in, at least, packaging and labeling.
1 . A method of making a polylactic acid (PLA) blown film comprising (a) providing dry pellets of PLA, (b) melting the pellets to form a molten mass at a first desired viscosity value or range of values, (c) increasing the viscosity of the molten mass to a second desired viscosity value or range of values, (d) forming a bubble from the resulting molten mass, and (e) collapsing the bubble to form a film, in which the PLA blown film is substantially free of plasticizer.
2 . The method of claim 1 in which the melting step is carried out at a temperature range of about 325° F. to about 485° F.
3 . The method of claim 1 in which the first viscosity value ranges from about 1,000 P to about 5,000 P at about 480° F. at an apparent shear rate of about 55 seconds −1 .
4 . The method of claim 1 in which the second viscosity value ranges from about 14,000 P to about 16,000 P at about 375° F. at an apparent shear rate of about 55 seconds −1 .
5 . The method of claim 1 in which the viscosity increasing step is carried out in a polymer cooling unit.
6 . The method of claim 1 in which the step of forming a heated bubble includes a stretching step, which orients the film.
7 . The method of claim 1 which further includes annealing the film.
8 . The method claim 15 in which the annealing step is carried out at a temperature ranging from about 120° F. to about 285° F.
9 . The method of claim 1 in which the bubble is heated at a temperature greater than about 100° F.
10 . A blown film comprising a polylactic acid (PLA) polymer and substantially free of plasticizer.
11 . The blown film of claim 10 in which the PLA polymer has a molecular weight average of about 100,000 to about 400,000.
12 . The blown film of claim 10 in which the PLA polymer is greater than about 90 percent by weight polylactide.
13 . The blown film of claim 10 in which the blown film further comprises a second PLA polymer.
14 . The blown film of claim 10 in which the PLA polymer has a mesolactide level of about 10 percent to about 20 percent.
15 . The blown film of claim 10 in which the film further comprises a colorant.
16 . The blown film of claim 15 in which the colorant is present at a concentration between about 1 to about 20 percent by weight.
17 . The blown film of claim 15 in which the colorant is TiO 2 .
18 . A packaged good comprising a consumable item and a PLA blown film according to claim 10 wrapped around at least a portion of the consumable item.
19 . An envelope having a front wall and a rear wall, one of said walls being provided with at least one window, in which the window comprises a blown film according to claim 10 .
20 . A blown film comprising a polylactic acid (PLA) polymer and less than about 2 weight percent plasticizer.