Barrier Properties of Biodegradable Bacterial Polyester Films - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 72

Water and Gas Permeation
The permeation mechanisms depend mainly on the chemical nature of the polymer
backbone and the characteristics of the diffusing molecules. It is well-known that dif-
fusing gas molecules, except for CO 2 , have no, or at least very few, interactions with
polymer materials. It is important to know the conditions of permeation measurements
carried out however this information is unfortunately often forgotten in the literature.
Added to this fact, few data about permeation in literature are available as well as in
great diversity of units which makes it difficult to establish comparisons.
Some selected data are presented in Table 2 with some common polymers.

table 2. Gas Permeability of Common Polymers Available for Packaging Applications.

CO 2 P (barrer) O 2 P (barrer) N 2 P (barrer) H 2 O P (barrer)

Linear PLA 96:4 (25°C)
Cargill-Dow Polymers
Crystallinity 1,5%

9.8 3.15 1.3 -

Linear PLA 98:2 (25°C)
Cargill-Dow Polymers
Crystallinity 2,5%

9.6 3.1 1.2 -

Linear PLA 96:4 (30°C)
Cargill-Dow Polymers

10.2 3.3 1.3 6200

PET (30°C) 0.2 0.04 0.008 130

LDPE (30°C) 28.0 6.9 1.9 72

PS (30°C) 10.5 2.6 2.2 -

PP (30°C) 2.9 - - 51

PHB (25°C)
Biomer P209
Crystallinity 40%

9.3 1.4 0.74 4743

PHB (25°C)
Biomer P226
Crystallinity 45%

2.3 0.5 0.13 2544

PHBV (25°C)
Tianan Y1000P
Crystallinity 57%

0.15 0.1 0.02 897

Data depended on temperature tested.
Source: Williams, 1969; Rogers, 1985; Miguel, 1997; Lehermeier, 2001; Follain, 2010.

Concerning gas permeation measurements, although PET, PLA, and PHBV
copolymers are both polyester backbones, PET contains aromatic rings in the chain
structure which reduces free volume and chain mobility. This results in the lower per-
meation for PET. The main difference between PLA and PHB polymers is based on the
crystal organization inside material and the crystallinity degree which is found higher
for PHB copolymers. This results in the lower permeation for PHB polymers. The
measurements showed that crystallinity significantly impacts permeation process. The
crystalline domains are thought to alter the diffusion pathway of diffusing molecules since