242 Introduction to Renewable Biomaterials
Table 8.3Influence of molecular weight and content of triethyl citrate (TEC) and acetyl tributyl
citrate (ATBC) on polylactic acid thermal properties.
Sample (numbers
represent ratios) Name
Crystallinity
(%) Tc(∘C) 횫Hc(J g−^1 ) Tm(∘C) 횫Hm(J g−^1 )
Treated PLA TrtPLA 0.45 131 .81 4.937 152.03 4.517
PLA 95/TEC 5 PLA-TEC5 2.61 120 .87 16.12 148.92 18.43
PLA 90/TEC 10 PLA-TEC10 3.32 119 .67 9.640 147.97 12.42
PLA 85/TEC 15 PLA-TEC15 3.84 104 .42 20.19 145.94 23.23
PLA 80/TEC 20 PLA-TEC20 5.88 91 .63 18.52 143.52 22.90
PLA 70/TEC 30 PLA-TEC30 7.49 70 .56 10.95 138.55 15.83
PLA 95/ATBC 5 PLA-ATBC5 1.35 115 .73 20.07 146.96 21.27
PLA 90/ATBC 10 PLA-ATBC10 2.68 111 .56 20.77 150.08 23.02
PLA 85/ATBC 15 PLA-ATBC15 3.42 101 .06 23.68 148.07 20.97
PLA 80/ATBC 20 PLA-ATBC20 4.36 92 .01 19.61 146.74 22.86
PLA 70/ATBC 30 PLA-ATBC30 9.73 71 .75 13.90 143.20 20.24
Adapted from ref. 5.
PEG and OLA acted as best plasticizers, with decreasing glass transition temperature,
melting point and increasing up to 200% the elongation at break. As always, the
plasticizer effect was also evident in a decrease in elastic modulus.
The influence of molecular weight and content of plasticizers introduction was
analysed by Maizaet al. [5]. They evaluate the effect of different percentages of
triethyl citrate (TEC) and acetyl tributyl citrate (ATBC) on properties of films for food
packaging made of PLA.
Increasing the plasticizer contents leads to lowerTg, melting and crystallization
temperature and melting and crystallization heat. Meanwhile, an increased crystallinity
was experienced with the rise of the plasticizer. Some results are shown in Table 8.3
and Figure 8.1.
During last years, a new method of improving PLA toughness has been developed
through addition of ionic liquids, which are molten salt, achieving great atten-
tion because of their high thermal stability, low vapour pressure, recyclability and
non-flammability; moreover, ionic liquids are considered as green solvents.
Ionic liquids are characterized by liquid in which the ions are slightly coordinated,
reaching low melting points (below 100∘C). Their structure is generally composed
of organic cations and inorganic anions, influencing their properties. In fact, the
low melting point is a direct consequence of organic cation asymmetry compared to
inorganic part: in this way, lactic energy is low and so the melting point.
They are usually categorized into four different families on their cations:
Imidazolium ion
N N
R R′
+
Pyridinium ion
N
R
+
Ammonium ion
N +
R
R
R
R′
Phosphonium ion
P +
R
R
R
R′
