Abstract In presented work, the blends composed from pure polylactic acid (PLA) and starch oleates were examined. Starch oleates (SO) with different degree of substitution (DS) were prepared by esterification of native starch and oleoyl chloride in heterogeneous conditions (pyridine). These prepared starch esters were used in the function of additives for preparation of blends with PLA. The PLA/starch oleates blends (9:1) have been prepared and evaluated by using attenuated total reflectance (ATR) spectroscopy technique. Subsequently, their mechanical properties, such as storage modulus (E&apos;), loss modulus (E&apos;&apos;) and tan D were studied as a function of temperature by dynamic mechanical thermal analysis (DMTA). These blends containing 10 wt. % SO show satisfactory mechanical properties in comparison to pure PLA

Iva Sroková

Jarmila Kebísková

Mária Chromčíková

Vlasta Sasinková

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University Review, Vol. 6, 2012, No. 2   ISSN 1337-6047 
 
 38 
 
PREPARATION AND STUDY OF MECHANICAL PROPERTIES OF 
POLYLACTIC ACID/STARCH OLEATES BLENDS 
 
Jarmila Kebísková
1*
, Iva Sroková
1
, Vlasta Sasinková
2
, Mária Chromčíková
3
 
 
1Faculty of Industrial Technologies, University of Alexander Dubček in Trenčín, I. Krasku 1809/34, 020 01 Púchov, Slovakia  
2Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 38 Bratislava, Slovakia 
3Vitrum Laugaricio – Joint Glass Centre of the Institute of Inorganic Chemistry SAS, University of Alexander Dubček in 
Trenčín , CHFPT STU and RONA, j.s.c., Študentská 2, 911 50 Trenčín, Slovakia 
* Corresponding author E-mail address: jarmila.kebiskova@fpt.tnuni.sk 
  
Received 16. 10. 2012; accepted in revised form 06. 12. 2012 
 
 
Abstract 
In presented work, the blends composed from pure polylactic acid (PLA) and starch oleates were examined. Starch oleates 
(SO) with different degree of substitution (DS) were prepared by esterification of native starch and oleoyl chloride in 
heterogeneous conditions (pyridine). These prepared starch esters were used in the function of additives for preparation of 
blends with PLA. The PLA/starch oleates blends (9:1) have been prepared and evaluated by using attenuated total reflectance 
(ATR) spectroscopy technique. Subsequently, their mechanical properties, such as storage modulus (E'), loss modulus (E'') 
and tan D were studied as a function of temperature by dynamic mechanical thermal analysis (DMTA). These blends 
containing 10 wt. % SO show satisfactory mechanical properties in comparison to pure PLA. 
 
Keywords: starch oleates, PLA, blends, mechanical properties 
 
 
1  Introduction 
An increasing interest in the recycling and the use of biodegradable materials, together with improved 
thermo-mechanical properties of polymer blends has led to the use of polysaccharides as biodegradable filler. 
The greatest application of polysaccharides, especially starch, cellulose, xylans, galactomannan and their 
derivatives in the polymer field are as a component in various polymer formulations [1]. Starch and cellulose 
polymers derived from biofeedstocks are also finding use directly or as blends with other biobased and 
biodegradable polymer materials [2]. Starch is one of the most studied and promised raw materials for 
biodegradable plastics because of its natural abundance and low cost, otherwise, starch and its derivatives have 
better reactivity than the other biodegradable natural biopolymers, such as cellulose, chitin, etc. [3,4]. Natural 
starch is rarely used in the function of the additive itself, because is hydrophilic. The hydrophilic nature of starch 
is a major constraint that seriously limits the development of starch-based materials, in fact, their properties 
depend on the ambient humidity. To improve its properties must be physically and chemically modified. 
Chemical modification involves the introduction of functional groups into the starch molecule, using 
etherification and esterification or decomposition reactions. This is a useful alternative that allows to modify the 
structure and consequently the properties of natural starch [5].  
Poly(lactic acid) (PLA), produced from renewable resources like corn, is one of the most important 
biodegradable polyester with good mechanical properties, high transparency and good processability. However, 
disadvantages such as brittleness, poor thermal stability, and high costs limit its applications in general use 
plastics such as industrial packaging and agricultural films. Therefore, it is necessary to modify PLA for 
commercial applications in order to improve its properties (to overcome the limitation of its inherent brittleness) 
and reduce its cost [4,6]. Many properties of PLA are comparable to those of polyethylene, polypropylene, 
polystyrene, and polyethylene terephthalate, such as stiffness, tensile strength, and gas permeability. However, 
PLA is more expensive than conventional petroleum polymers for disposable or short-term applications [7]. 
PLA and starch are good candidates for polymer blends, since both are biodegradable, made from renewable 
resources. Starch improves biodegradability, increases heat resistance and also reduces cost while PLA offers 
superior mechanical properties [2]. Starch has been used as filler in blends with PLA, but the mechanical 
properties of the blends decreased significantly with increased starch content [7]. The goal of blending 
completely degradable polyester (PLA) with low cost starch is to improve its cost competitiveness whilst 
maintaining other properties at an acceptable level [8]. 
 
 
 
 
University Review, Vol. 6, 2012, No. 2   ISSN 1337-6047 
 
 39 
2  Experimental  
Materials 
      The polylactic acid (PLA) was obtained from VÚCHV, Inc. (SVIT, Slovakia). Native starch was supplied 
from Spolana, Inc. (Neratovice, Czech Republic) and for experiments it was dried at 105 °C for 1 h. The oleoyl 
chloride and dichlormethane were purchased from Aldrich Chemie (Steinheim, Germany). The pyridine and the 
ethanol were of standard purity, supplied by the AFT Ltd. (Bratislava, Slovakia). 
 
Esterification of starch  
      The esterification of starch with oleoyl chloride was carried out in an analogous way by method used for the 
modification of native starch with octanoyl chloride [9]. Starch oleates (SO) with different degree of substitution 
(DS) have been prepared by esterification of starch with oleoyl chloride in pyridine at constant weight ratio 1:3 
and at temperature 105 ºC with reaction time 6 and 3 h., respectively. It has been reported in Table 1. 
      The two methods of heating were used for esterification: classical heating and microwave heating (MW), 
which was used for shortening of reaction time from hours to minutes. Microwave device stood for the 
microwave oven which is normally used in households but this oven was suitably modified for the experimental 
conditions.   
 
                        Table 1  Esterification of starch with oleoyl chloride (1:3) in pyridine at 105 ºC and DS 
Starch oleate 
(SO) 
Reaction time 
(h,min) 
Degree of substitution 
(DS) 
SO1005 6 h 1.85 
SO1006 3 h 1.30 
SO1009* 2.5 min 2.67 
 
 
Preparation of PLA/SO blends (9:1) 
      PLA/SO blends were prepared as follows: 0.1 g of the starch oleate was dissolved in 10 ml of 
dichloromethane (CH2Cl2) under stirring for 24 h at room temperature in a beaker with a lid. Then 0.9 g PLA was 
added to the mixture and stirred at room temperature until the PLA was dissolved. Prepared mixture of PLA/SO 
was spilt on Petri dish (diameter 9.5 cm) and then the mixture was let to be evaporated spontaneously in the dark 
place for 24 h.  
      For comparison purposes was also prepared standard from pure PLA as follows: 1 g PLA was dissolved in 10 
ml of dichloromethane (CH2Cl2) by stirring at room temperature in a beaker with a lid. Then the prepared 
mixture of PLA was spilt on Petri dish (diameter 9.5 cm) and then the mixture was let to be evaporated 
spontaneously in the dark place for 24 h.  
 
Characterizations 
      The ATR spectra were measured on a NICOLET 6700 spectrometer by ATR technique. For each spectrum 
128 consecutive scans with 4 cm
-1
 resolution was averaged. Company: SHIMADZU Corporation, Kyoto, Japan.  
      Dynamic mechanical thermal analysis (DMTA) was carried out on a TMA Q400 EM, TA instrument. DMTA 
was used for comparison of the stress and strain signals and resolution of the strain into the in-phase (storage) 
and out-of-phase (loss) components, from which storage or elastic (E') and loss (E'') moduli as well as tan D = 
E''/ E' were obtained as a function of temperature. The range of temperature of measurements was from 40 to 75 
C. The used standard heating rate was 3 °C/min, under a periodic load between 0.08 and 0.06 N at frequency of 
0.5 Hz. Test samples, which were used for evaluation of mechanical properties had dimensions (W x T x L = 4.5 
x 0.2 x 16 in mm). A drop in storage modulus and a peak in tan D were used as indicators of a glass transition.          
 
3  Results  
ATR measurements 
      The compatibility of the polymer blends was also characterized by ATR spectroscopy. For compatible 
polymer blends, the ATR spectrum band would considerably deviate or be obviously shifted (band frequency 
shifting, along with peak style asymmetrically widening), compared to that of the single polymer component. 
However, for the completely incompatible polymer blends, the characteristic absorption spectrum would overlap 
perfectly, compared to the single polymer component [9,10].  
Figure 1 depicts the ATR spectra of PLA/starch oleates blends (9:1) and pure PLA in region 2700-3100  cm
-1
. 
There are no significant differences observed in the spectra of the blends with PLA (e. g. peak shifts) in 
comparison to the spectrum for pure PLA. Only few changes may be observed in these spectra, especially in 
University Review, Vol. 6, 2012, No. 2   ISSN 1337-6047 
 
 40 
some peak intensities. The strong bands at 2851 cm
-1
 and 2924 cm
-1
, can be assigned to the methyl/methylene 
groups of starch oleates in the blends with PLA. In comparison to PLA, the given ATR spectra of the blends 
showed differences and therefore it can be concluded that prepared blends are compatible. 
 
 
Fig. 1 ATR spectra of PLA/starch oleates blends (9:1) and PLA  
          
Mechanical properties  
      DMTA method is a very useful technique for study of the viscoelastic response of the polymers as well as 
their composites in a wide range of temperatures. Using DMTA method was determined the storage modulus 
(E'), loss modulus (E'') and tan D of PLA/starch oleates blends and pure PLA as a function on temperature. The 
DMTA data, i.e. the storage modulus (E'), loss modulus (E'') and tan D of selected polymer blends as well as 
pure PLA are shown in Figs 2, 3 and 4, respectively. 
 
      The behaviour of storage modulus E' for selected PLA/starch oleates blends and pure PLA is shown in Fig. 2. 
As can be seen that storage modulus E' of unmodified PLA and PLA/SO blends shows various behavior. The 
selected PLA/SO blends showed slightly decreased storage modulus E' from cca 200 MPa up to 100 MPa at the 
temperature ~ 50 °C and then the storage modulus E' increased rapidly to the maximum temperature at ~ 55 °C 
for both derivates with maximum ~ 400 MPa for derivate (SO1009) with DS = 2.67 and ~ 200 MPa for derivate 
(SO1006) with DS = 1.3 and then it decreased again to zero MPa at the temperature about 70 °C to the modulus 
of initial PLA.  
 
Fig. 2 Dependence of storage modulus E' of selected polymer blends and PLA on temperature 
 
The storage modulus E' is an important parameter for rigid materials. Storage modulus or dynamical modulus 
characterizes behaviour of materials as a reversible component of complex modulus after low oscillation strain or 
stress. The dependence of storage modulus E' is influenced by the presence of starch oleates in a blends with 
40 50 60 70 
0 
200 
400 
600 
800 
1000 
    
  
  
Storage modulus / MPa 
Temperature / °C 
  PLA-ST/SM_2 
   10% SO1006+PLA/SM 
   10% SO1009+PLA/SM 
 2851 
 2924 SO-1005 + PLA   10% 
SO-1006 + PLA   10% 
SO-1009 + PLA   10% 
PLA   Smart Orbit 
-0,018 
-0,016 
-0,014 
-0,012 
-0,010 
-0,008 
-0,006 
-0,004 
-0,002 
 0,000 
 0,002 
 0,004 
 0,006 
 0,008 
 0,010 
 0,012 
Absorbance 
 2700    2800    2900    3000    3100    3200   
Wavenumbers (cm-1) 
University Review, Vol. 6, 2012, No. 2   ISSN 1337-6047 
 
 41 
PLA. Storage modulus of starch oleates was lowered at temperature 45-50 ºC and it means that SO have positive 
effect. This modulus characterizes the stiffness of PLA/polysaccharide blends and it is lower than PLA.   
 
 
Fig. 3  Dependence of loss modulus E'' of selected polymer blends and PLA on temperature 
 
      Fig. 3 presents the dependence of the loss modulus E'' of selected polymer blends and PLA on temperature 
and as can be seen, the dependence of the loss modulus E'' is affected by the presence of starch oleates in a 
mixture with PLA. Although there was the low addition of additives (10 wt. %) in a mixture of PLA, the loss 
modulus of the PLA/SO blends was increased together with temperature and DS of starch oleates in the blends 
and due to this fact there was the influence on the dependence of tan D on the temperature. 
 
 
Fig. 4  Dependence of tan D of selected polymer blends and PLA on temperature 
 
      The tan D of selected PLA/starch oleates blends and PLA (9:1) is shown in Fig. 4. From the dependence tan 
D = f (temperature) can be evaluated the temperature of glass transition (Tg) of polymer blends [11]. From the 
diagram for the pure PLA and PLA/SO blends it can be concluded that these blends have Tg in the range 60-65 
°C and it is also confirmed by literature [12]. 
 
4  Conclusion 
 Starch oleates (SO) with different degree of substitution (DS) were prepared and used in the function of 
additives for preparation of polysaccharide blends with PLA. 
Subsequently, the mechanical properties of the selected PLA/starch esters blends were evaluated by DMA 
method. The following conclusions have been drawn from this work: 
- DS of starch oleates were 1.3 -2.67; 
- the increase of storage modulus E' together with DS of starch oleates in the blends; 
- starch oleates in a blends with PLA had a positive effect on the stiffness of blends; 
- the relatively low content of additives (10 wt. %) in blends with PLA influenced the dependence of the loss 
modulus E''  as well as  the value of tan D; 
- from the dependence of tan D on temperature were evaluated temperature of glass  transition (Tg) at 60-65 ºC 
of prepared selected blends; 
40 50 60 70 
0.0 
0.2 
0.4 
0.6 
0.8 
1.0 
1.2 
  
  
  
  
Tan Delta 
Temperature / °C 
  PLA-ST/TnD_2 
  10% SO1006+PLA/TnD 
  10% SO1009+PLA/TnD 
40 50 60 70 
0 
20 
40 
60 
80 
100 
  
  
  
  
Loss modulus / MPa 
Temperature / °C 
  PLA-ST/LM_2 
  10% SO1006+PLA/LM 
  10% SO1009+PLA/LM 
University Review, Vol. 6, 2012, No. 2   ISSN 1337-6047 
 
 42 
- the PLA/starch oleates blends show satisfactory mechanical properties in comparison to pure PLA. This means 
that relatively low amounts of starch esters  
  (10 wt. %) can be tolerated in blends with PLA to obtain blends with acceptable  mechanical properties. 
 
Acknowledgements 
This work has been supported by VEGA grant No. 2/0062/09 
 
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 Review: Eugen Jóna 
    Anna Prnová 
 
   
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 


PREPARATION AND STUDY OF MECHANICAL PROPERTIES OF POLYLACTIC ACID/STARCH OLEATES BLENDS

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PREPARATION AND STUDY OF MECHANICAL PROPERTIES OF POLYLACTIC ACID/STARCH OLEATES BLENDS

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