and it is reasonable that the decrement is independent of the hydrophobility of the surfaces [27].
Although NR has enhanced the hydrophobility of the PLA sur- faces, water absorption does not decrease, on the contrary, NR seems has an effect on increasing water absorption. Fig. 2 shows the percentage moisture absorption of PLA and PLA/NR blends as a function of t1/2 at immersion temperature of 58 C which is also the hydrolysis temperature compared to the compost temperature in international standard [28]. There are four distinct chronological regimes on moisture absorption: (1) a quickly water absorption which is a simple water in-diffusion (t1/2 1⁄4 0e30), (2) moisture absorption does not increase with time increasing, the specimen reaches its water saturate (t1/2 1⁄4 30e100), (3) water uptake begins again and absorption rate increases with immersion time (t1/ 2 1⁄4 100e165), (4) the absorption reaches the maximum value and the moisture absorption seems to start decrease (t1/2 > 165).
At the initial stage, the higher NR content leads to the more rapidly moisture absorption. Generally, water permeation in poly- mers is always affected by the packing density of polymer chain segments [12,17]. For non-crosslinked NR, it has a bigger intermo- lecular distance than PLA, which can be confirmed by the lower