INVESTIGATION IN THE MANUFACTURE OF NON-WOVENS FROM POLYLACTIDE BY SPUNBOND METHOD

1
INVESTIGATION IN THE MANUFACTURE OF NON-WOVENS
FROM POLYLACTIDE BY SPUNBOND METHOD

• K. Sulak1, M. Lichocik1, T. Mik1, I. Krucinska2,
  M. Puchalski2, J. Jarzebowski3
• 1Institute of Biopolymers and Chemical Fibers,M.
  Sklodowskiej-Curie 19/27, 90-570 Lodz, Poland,
  e-mail ibwch_at_ibwch.lodz.pl
• 2Technical University of Lodz, Faculty of
  Material Technologies and Textile Design,
  Department of Fibre Physics and Textile
  Metrology,Zeromskiego 116, 90-924 Lodz, Poland,
  e-mail nonwovens_at_p.lodz.pl
• 3Research and Development Centre of Textile
  Machinery Polmatex-Cenaro,Wólczanska 55/59,
  90-608 Lodz, Poland

BACKGROUND Poly(lactic acid) or polylactide
(PLA) is an aliphatic polyester that can be
produced from renewable materials such as corn,
sugar or vegetables1,2. The production of PLA is
based on the polycondensation of lactic acid or
the ring-opening polymerisation of lactide
obtained from the depolymerisation of oligomers
of lactic acid, which is a product of the
fermentation of biomass such as corn. In
comparison with conventional polymers, which are
produced from petroleum, PLA is an
environmentally friendly biodegradable polymer,
and it has attracted increased attention in
recent years. However, due to high manufacturing
costs, the use of PLA has been limited for many
years to medical applications3,4,5. A decrease in
the price of PLA expands the range of possible
applications. For example, PLA has become a major
starting material in the manufacture of
biodegradable textiles6. The preparation,
structure and properties of products made of PLA
and its modification are the subjects of
intensive scientific7 and technological
investigations. Compared with classical
polyesters such as polyethylene terephthalate
(PET), PLA products are characterised by a higher
water sorption of 0.4-0.6 and better resistance
to UV radiation. The latter feature, in
combination with biodegradability, makes
polylactide fibres and non-woven fabrics
particularly useful raw materials for the
preparation of disposable medical and hygiene
textiles. Other applications include technical
textiles used in filtration or in agriculture and
in cloth for garments and underwear. The ability
of PLA to crystallise depends strongly on the
stereochemical form of PLA and is different for
isotactic poly(L-lactide) (PLLA) or
poly(D-lactide) (PDLA), syndiotactic
poly(meso-lactide), atactic poly(meso-lactide) or
poly(D,L-lactide), PLLA/PDLA stereocomplexes and
copolymers with random levels of meso-, L-, and
D-lactide. As a consequence, the physical
properties of fabrics manufactured from different
PLAs can be differ. Moreover supermolecular
structure of PLA fabrics strongly depends on the
stereoregularity of the PLA form of the polymer
and the technological conditions applied during
the fibre manufacturing process. Therefore, it is
important to elucidate the relationships between
the conditions of formation and the properties of
the resulting fabrics.
RESULTS Structural properties of PLA spun-bonded
non-woven fabrics Mechanical
properties of PLA spun-bonded non-woven
fabrics
Fig. 1. DSC thermograms recorded during the first
heating
Table 1. DSC calorimetric data obtained for the
investigated variants of spun-bonded, non-woven
fabrics.
Temperature of calender (C) Degree of crystallinity (wt. ) Glass transition temperature Tg,(C) Cold crystallisation temperatureTc,(C) Melting temperatureTm ,(C) Enthalpy of cold crystallisation ?Hc, (J/g) Change in heat capacity ?Cp, J/gC) Enthalpy of melting ?Hm (J/g)
70 21 66 76 166 28.3 2.52 47.9
75 20 66 75 167 29.9 2.12 48.8
80 40 66 80 166 10.9 0.69 47.9
85 54 66 - 165 - 0.34 49.6
90 54 65 - 165 - 0.19 50.3
95 55 65 - 165 - 0.29 51.1
100 54 65 - 164 - 0.34 50.1
105 54 64 - 164 - 0.17 50.7
110 56 65 - 164 - 0.22 52.3
120 56 64 - 164 - 0.17 51.1
130 55 64 - 164 - 0.15 50.0
Fig. 2. Relationships between the calculated
degree of crystallinity and the change in heat
capacity (?Cp) for each sample stabilised at
different thermal conditions.
The data in Table 1 and Figure 2 clearly
indicate that the elevation of the stabilisation
temperature to 85C markedly increased the
crystallinity level of the fibres, which limited
or even eliminated the possibility of cold
crystallisation during heating.
Fig. 3. Changes of the mechanical properties of
nonwoven fabrics stabilised at different thermal
conditions in the machine (MD) and transverse
(TD) directions a) tenacity of non-woven fabrics
and b) elongation at break of non-woven fabrics.
AIM OF WORK The aim of work was to determine the
influence of different forming parameters
(especially thermal conditions of stabilisation
at the embossing roll of the calender) on the
physical and mechanical properties and
supermolecular structure of PLA spun-bonded
nonwoven fabrics.
MATERIALS AND TEST METHODS Raw material Non-woven
fabrics were manufactured from commercially
available PLA 6251D (Nature Works LLC, USA)
specifically designed for the spun-bonded
technology. A molar mass of PLA 6251D Mn of 45
800 g mol-1 and a polydispersity Mw/Mn of 1.29
were determined by size-exclusion chromatography
(SEC) with a multi-angle light scattering (MALLS)
detector in methylene chloride. The D-lactide
content was 1.4, as determined based on the
specific optical rotation measurements. The glass
transition temperature (Tg) and melting
temperature (Tm), determined by differential
scanning calorimetry (DSC), were equal to 61C
and 128C, respectively. Drying of polymer To
reduce the moisture content below 50 ppm, prior
to spinning, the PLA was dried for at least 4 h
at 80C (dew point -30C) in a Piovan dryer that
is part of the laboratory setup for studying
non-woven fabrics manufacturing with the
spun-bonded technique. The moisture content in
the polymer was measured by the Karl Fischer
coulometric method using the DL39X apparatus
(Mettler Toledo). Spun-bonded technology
details The non-woven fabrics were formed by a
spun-bond technique on a laboratory line designed
and constructed by the Research and Development
Centre of Textile Machinery Polmatex-Cenaro,
Poland. The process parameters were as follows a
temperature in the range from 205C to 216C and
a polymer throughput in the range of 0.10-0.43
g/min/hole can be used. A spinneret with 467
holes was used. The calender temperature was
varied from 60C to 130C. Thermal
properties For characterisation of the thermal
properties of fabrics formed under the various
manufacturing conditions, DSC measurements were
carried out using a Q2000 (TA Instruments, UK).
Specimens were first heated from 0?C to 250?C and
then cooled to -30?C and immediately reheated to
250?C at a rate of 10?C/min. Mechanical
properties The tensile strength and elongation
analysis of the studied spun-bonded fabrics was
conducted using the mechanical testing machine
Instron 5511 according to EU standard EN
29073-31992 Methods of test for nonwovens.
Determination of tensile strength and
elongation. Shrinkage analysis The changes in
the dimensions of the non-woven fabrics in hot
air (both the length and width) were determined
in accordance with standard ISO 37592011
Textiles - Preparation, marking and measuring of
fabric specimens and garments in tests for
determination of dimensional change.
Fig. 4 Changes in the length of the investigated
samples in the machine direction as a function of
the stabilisation temperature.
When the stabilisation temperature rises above
85C, the degree of crystallinity increases to a
maximum value of approximately 55, the overall
molecular orientation increases and the ordered a
crystals are developed. The development of such a
supermolecular structure results in stability of
the fabric dimensions in hot air.
CONCLUSION Results showed the rebuilding of the
supermolecular structure of the investigated
samples of PLA fabrics under the influence of
different stabilisation temperatures adjusted at
the embossing roll in the range of 70-130C. The
crystallinity degree increased to 54 when the
temperature of the calender was changed to 85C.
Further increases of the stabilisation
temperature did not have any significant
influence on the crystallinity degree of the
tested samples. The increased crystallinity
level was reflected in the reduction of thermal
shrinkage and in the increase of the stress at
the breaking point of the investigated samples.
The maximum value of the stress at the breaking
point was observed for PLA non-woven fabrics
stabilised at a temperature of 90C. The
stabilisation of non-woven fabrics in the optimum
temperature range of 85-100C made it possible to
reach high values for the stress at the breaking
point and small values of thermal shrinkage. An
insignificant increase of the strain at the
breaking point was observed for the ordered
crystalline phase of PLA.
B
A
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ACKNOWLEDGEMENT The presented research was
performed within the framework of the key project
titled Biodegradable fibrous products (acronym
Biogratex) supported by the European Regional
Development Fund Agreement No.
POIG.01.03.01-00-007/08-00.