Polylactides—Chemistry, Properties and Green Packaging Technology: A Review

Figures & data

Figure 1 Stereoisomers of lactic acid.

Figure 2 Polymerization reaction of lactic acid.

Figure 3 Schematic representation for polymerization of lactic acid.

Figure 4 Diasteroisomeric forms of lactides.

Table 1 Effect of isomer on thermal properties of PLA

Isomer type	Mn × 10^3	Mw/Mn	Tg (°C)	Tm (°C)	ΔH (J/g)	Tc (°C)	ΔH (J/g)
L	4.7	1.09	45.6	157.8	55.5	98.3	47.8
DL	4.3	1.90	44.7	–	–	–	–
L	7.0	1.09	67.9	159.9	58. 8	108.3	48.3
DL	7.3	1.16	44.1	–	–	–	–
D	13.8	1.19	65.7	170.3	67.0	107.6	52.4
L	14.0	1.12	66.8	173.3	61.′	110.3	48.1
D	16.5	1.20	69.1	173.5	64.6	109.0	51.6
L	16.8	1.32	58.6	173.4	61.4	105.0	38.1

Figure 5 Thermograms for A. L-PLA and B. DL-PLA.

Figure 6 Typical FTIR spectra for PLA (L-form). (Figure provided in color online.)

Figure 7 PLA based food packaging. (Figure provided in color online.)

Table 2 Potential food application of PLA based packaging materials

Type of food	Film properties	Commercial manufacturer	References
Bottled water	Moisture, light and gas barrier	Biota^TM
Bottled juice	Moisture, light and gas barrier, inert to migration of flavor	Noble^TM	[44–45]
Milk	Moisture, light and gas barrier
Yoghurt	Mechanical strength, barrier of oxygen, carbon dioxide, moisture and grease	Dannon^TM
Cheese	Moisture, light and gas barrier
Butter/Margarine
Mushroom	Mechanical strength, balanced gas and moisture barrier; protection against crushing/bruising		[44–45]

Figure 8 Typical pressure effect on crystallization of PLA. (Figure provided in color online.)

Table 3 Comparison of thermal properties (heating rate 10°C/min) of PLA and synthetic polymers.*

Sample	Mn×10^3	Tg (°C)	Tm (°C)	Tc (°C)
Polyethylene terephthalate (PET)	100	90.5	257.7	216.6
Polyethylene	103		98.8	76.7
Polystyrene (atactic)	99	98.5
PLA (L-form)	150	66.9	179.8	–
PLA (DL-form)	250	53.1	–	–
*Authors unpublished data.

Table 4 Comparison of water vapor and oxygen transmission rate of PLA and synthetic polymers.*

Sample	Thickness (mm)	WVTR [g(m^2/d)]	Permeability coefficients [kg/m/(m^2/s/Pa)]	OTR [cc(m^2/d)]	Permeability coefficients [kg/m/(m^2/s/Pa)]
PET	18	3.48	2.82×10−^15	9.44	6.95×10−^19
PS	18	5.18	4.18×10−^15	531.58	3.91×10−^17
PLA	20	15.30	1.34×10−^14	56.33	4.33×10−^18
*Adapted from Auras et al.[29]

Figure 9 Typical sorption isotherm of PLA film (L-form).

Figure 10 Quartz Crystal Microbalance used for sorption studies of PLA. (Figure provided in color online.)

Figure 11 Nanoclay-PLA synthesis schematic diagram.

Table 5 Thermal and rheological data of nanoclay incorporated PLA composite

Sample	Composition (% wt.)		Mw×10^3	Tg (°C)	Tm (°C)	χc (%)	G′ (GPa)
	PLA	Mmt*					−20°C	40°C	100°C	145°C
PLA	100	0	187	60.0	168	36.2	1.74	1.60	0.13	0.06
NC1	97	3	178	60.0	169	50.7	2.32	2.07	0.16	0.09
NC2	95	5	185	60.0	170	39.0	2.90	2.65	0.25	0.10
NC3	93	7	177	59.8	170	43.7	4.14	3.82	0.27	0.19
*Mmt: montmorillonite. Adapted from Sinha Ray et al.[15]

Table 6 Characteristics of typical bioresorbable PLA based polymers

Polymer	Tm (°C)	Tg (°C)	Modulas (GPa)	Degradation time (months)
Poly(lactic acid) (L-form)	173–178	60–65	2.7	>24
Poly(lactic acid) (DL-form)	Amorphous	55–60	1.9	12–16
Poly(DL lactic acid-co-glycolic acid) (75/25)	Amorphous	50–55	2.0	4–5
Poly(DL lactic acid-co-glycolic acid) (50/50)	Amorphous	45–50	2.0	1–2
*Adapted from Zilberman and Eberhart.[82]

Tsuji , H. , Horii , F. , Nakagawa , M. , Ikada , Y. , Odani , H. and Kitamaru , R. 1992 . Macromolecules , 25 : 4114 – 4118 .

 Web of Science ®Google Scholar

Sinha Ray , S. , Maiti , P. , Okamoto , M. , Yamada , K. and Ueda , K. 2002 . New polylactide/layered silicate nanocomposites. 1. Preparation, characterization and properties . Macromolecule , 35 : 3104 – 3110 .

 Web of Science ®Google Scholar

Zilberman , M. and Eberhart , R.C. 2006 . Synthetic Biodegradable Polymers as Medical Devices from The Annual Review of Biomedical Engineering , 8 : 153 – 180 .

 PubMed Web of Science ®Google Scholar