Meltblown Elastic Nonwovens from Specialty Polyolefin

Meltblown Elastic Nonwovens from Specialty Polyolefin Elastomers
Raja Dharmarajan
Smita Kacker
Vincent Gallez
A.D Westwood
C.Y Cheng (consultant)
ExxonMobil Chemical Company
5200 Bayway Drive
Baytown, TX 77520
Introduction:
Specialty Polyolefin Elastomers (SPE) are a new generation of metallocene catalystbased polymers endowed with isotactic propylene crystallinity. They can be processed in
conventional spunmelt equipment to produce elastic nonwoven fabrics. For meltblown
applications, SPE resins were developed at a nominal melt flow rate (MFR) of either 200
or 300 g/10 min for processability considerations. The crystallinity of the SPE resins can
be adjusted through variations in the comonomer content, which results in nonwovens
with varying levels of elasticity. In this paper, the nonwoven characteristics of SPE A
polymer (lower crystallinity, 200 MFR) and SPE B polymer (higher crystallinity, 300
MFR) are characterized as a function of process parameters such as die to collector
distance (DCD), air gap settings, and fabric basis weight. Formulations of these SPE
resins, blended with conventional meltblown PP (1600 MFR) over a wide range of blend
compositions, are also discussed in this work.
Meltblown elastic nonwovens comprising SPE polymers offer a novel elastomeric
product that can be used in applications such as hygiene, personal care, medical and
industrial fabrics. The compatibility of SPE resins with other polyolefins provides a
useful tool in fine-tuning the nonwoven attributes to suit customer end use applications.
Experiments:
Meltblown elastic nonwovens were produced on a 0.5 m Reicofil® pilot line using SPE
resins varying in MFR from 80 to 300. For each SPE resin, the process air temperature
and air volume were suitably optimized to produce nonwovens relatively free of shots
and other defects. The parameters varied during meltblown processing of the SPE resins,
were die to collector distance from 178 to 250 mm, set back / air gap settings of 0.7/0.8
mm and 1.2/1.2 mm respectively, and fabric basis weight from 15 to 100 gsm.
Blends of SPE resins with PP were prepared by dry blending in a cement mixer and then
introducing directly into the extruder hopper. The SPE to PP ratio was varied broadly
from 0 to 100 %, DCD from 178 to 254 mm, while the set back/air gap was maintained at
the 1.2 mm /1.2 mm setting. The melt temperature of the die was maintained at 245 oC.
SPE nonwovens that do not contain PP as a blend component require a slip additive to
enable release of the fabric from the forming belt, particularly at low basis weight. The
slip masterbatch contains a blend of Erucamide to PP (30/70). Typically 2 to 4 wt. % of
the masterbatch (6000 to 12,000 ppm) is required to release the fabric from the forming
belt and mitigate blocking of the rolls.
Results and Discussions:
SPE Nonwovens
Figure 1 is a radar plot that compares the nonwoven properties of SPE A (200 MFR) with
SPE B (300 MFR) resin, respectively. The plot is constructed with the desirable
properties shown radially outwards from the center. The lower crystallinity in SPE A
provides enhanced elastic properties, notably lower permanent set, load loss and
mechanical hysteresis. With SPE B resin, the nonwoven shows marginally enhanced
tensile properties and improved barrier properties (higher hydrohead, lower air
permeability). The improvement in barrier is a result of the smaller fiber size seen in SPE
B, owing to the lower resin viscosity.
Figure 2 shows the comparisons between the 0.7 / 0.8 mm setting with the 1.2 / 1.2 mm
settings for set back / air. As seen in the Figure, the 1.2 mm settings provide an enhanced
balance of properties.
35 GSM, DCD = 198
SPE A, GSM = 35, GHM = 0.4, DCD = 254 mm
Tensile @ Pk M D (g/cm)
M ech H yst C D
70
60
60
M ech H yst M D
(%)
250
60
Load Loss C D 70
Load Loss M D
Elong. @ P k M D
300 Elong. @ P k C D
18
70
S et C D
20
180
A ir Perm .
Set M D
(cfm)
(%)
Figure 1: Comparison of SP A
and SPE B
SPE
B
V M 2330
Tensile @ Pk MD
Mech Hyst CD
70
60
Tensile @ PK CD
70
0.7 / 0.8
Mech Hyst MD 60
300 Elong. @ PK MD
Load Loss CD 75
H yd rohead
(mbar)
(%)
20
SPE A
SPE B
V M 2320
SPE
A
Tensile @ PK C D
250 Elong @ PK CD
12
75
Load Loss MD
20
Set CD
Hydrohead
200
15
Air Perm
Set MD
Figure 2: Effect of Set Back &
Air Gap on SPE A
Figure 3 shows the variation of nonwoven elongation to break of SPE A with process
parameters. The figures are response surface plots constructed from regression analysis.
The adjusted R2 values are 0.8 and 0.93 for Figures 3(a) and 3(b), respectively
In Figure 3(a), the elongation in MD (machine direction) improves with lower MFR or
higher molecular weight, with SPE A (200 MFR) having a higher elongation compared to
1.2 / 1.2
Elong @ Pk CD (%)
Elong. @ Pk MD (%)
(a)
320
240
160
80
(b)
400
346
238
130
80
64
200
48
225
Basis Weight
(gsm)
170
203
250
Resin M FR
(g/10 m in)
31
15
235
275
300
275
200
225
Resin MFR
(g/10min)
268
DCD (m m )
300 300
250
Figure 3: Variation of SPE A Nonwoven Elongation
(a) MD, 35 gsm
(b) CD, DCD = 254 mm
SPE B (300 MFR) at the same basis weight. Additionally lower DCD enhances
elongation owing to the uniformity in formation and laydown of the nonwoven. Figure
3(b) shows the trends in CD (cross direction) where elongation is enhanced by both lower
resin MFR and increasing basis weight of the fabric.
Nonwovens Comprising SPE A / PP Blends
Figure 4 shows the nonwoven elongation properties in MD and CD for blends of SPE A
and a conventional meltblown PP (1600 MFR) over a wide composition range. The data
(a)
(b)
250
200
150
20 gsm
50 gsm
100
50
0
0
10
30
50
70
80
85
VMA2320
Content(wt.
(wt. %)
SPE
Content
%)
90
Elongation @ Peak CD (%)
Elongation @ Peak MD (%)
250
200
150
20 gsm
50 gsm
100
50
0
0
10
30
50
70
80
85
90
SPE VM
A Content
(wt.
2320 Content
(wt.%)
%)
Figure 4: Elongation of SPE A / PP (1600 MFR) Blends at 178 mm DCD
(a) MD
(b) CD
was collected at a constant DCD of 178 mm. As seen in these Figures, the inclusion of
the elastic SPE A polymer enhances elongation of meltblown PP. The fabric elasticity is
also improved with increasing SPE A content. The elongation is greater than 100% at a
composition of 70 wt. % SPE A in the nonwoven. At this ratio the "hand properties" of
the nonwoven are closer to that of PP with a lower coefficient of friction. At 30 wt %
SPE A content, the fabrics are soft and drapable compared to PP nonwoven. Owing to the
inherent compatibility of SPE resins with PP homopolymer, the blends can be
compounded in-line, allowing fabric properties to be suitably tailored to meet end-use
applications.

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