A New Type of SIS Styrene Block Copolymer – Nonwovens Industry Magazine

TSRC, formerly known as Taiwan Synthetic Rubber Corp., has developed a new type of high strength and high elastic Styrene-Isoprene-Styrene (SIS) copolymer in response to the application requirements of personal hygiene elastic films. In addition to improving film strength, the new SIS also improves the material’s melt strength, making it more suitable for processing blown films. Odor performance has been significantly improved by new granulation equipment, which effectively reduces the amount of volatile organic compounds (VOCs).

TSRC was established in 1973 by founder Glyn TH Ing to support government policy on developing a petrochemical industry in Taiwan. TSRC has grown from a synthetic rubber manufacturer to a leader in today’s synthetic rubber and styrenic block copolymer (SBC) markets. The company’s products have been highly praised and widely adopted by major customers all over the world. TSRC’s annual output of SBR, BR, NBR, TPE, compounds and other synthetic rubbers has reached 805,000 tons. All of its manufacturing plants have successively obtained QC 080000 and ISO 50001 international certifications.

Headquartered in Taiwan, TSRC is vigorously expanding its business to establish production bases and sales teams in China (Nantong in Jiangsu and Song-Jiang in Shanghai), Thailand, India, Vietnam, the United States and Luxembourg. to meet the growing demand from customers around the world.

TSRC is a leading supplier of high quality Thermoplastic Elastomers (TPEs). The company uses advanced elastomer design and production technology to provide a series of styrene copolymer elastomer products and solutions.
SIS is the thermoplastic elastomeric polymer [1] which has the processing properties of plastic and elastic properties without the need for vulcanization. Among these properties, SIS has the following performance advantages for elastic films:

  1. Soft touch and comfortable fit
  2. High elasticity and good hysteresis performance
  3. Easy to recycle

Therefore, SIS is ideally suited for hygienic applications, such as: elastic constructions of baby diapers/adult incontinence products and three-dimensional elastic films of face masks.

In recent years, due to the growing demand for stretch film components, manufacturers have been looking for new ways to improve strength. This can be accomplished by adjusting the formulation of the compound according to the following two approaches:

I. High strength plastic is blended to increase film strength, but adding plastic sacrifices elastic properties.
II. Polystyrene resin can be added to increase the strength of the film, at the cost of creating a serious odor problem, which does not suit the personal hygiene market’s sensitivity to these problems.

The above formulation adjustment approaches must be combined with consideration of melt processing and converting equipment. A pre-mixing system, appropriate mixing extruder screws and film die configuration must be optimized to produce quality elastic film with uniform thickness.

On the other hand, due to the low melt strength of usual SIS, the bubble stability for blown film processing is insufficient, which limits the application of the material in blown film processing.
To solve the above-mentioned drawbacks of the usual SIS, TSRC improved the film and melt strength of this new SIS by increasing the styrene content and adjusting the molecular structure. A schematic diagram of the strength and elasticity of thin films based on new and conventional SIS is shown in Figure 1.


A. Materials:
The new high strength SIS VECTOR 4258ND/4359ND are developed as upgraded versions of SIS VECTOR 4111ND/4211ND respectively. The specifications of the new high-strength SIS VECTOR and traditional SIS VECTOR materials are shown in Table 1.

B. Preparation of Cast Film Samples:
Labtech experimental casting equipment (LCR300) was used to produce film samples. The associated equipment parameter settings are as follows:
I. Single screw temperature adjustment range: 170 ~ 220 ℃
II. Screw rotation adjustment: 30RPM
III. Output elastic film thickness: 100um

C. Film strength and elasticity test
An Instron 33R4464 tensile tester was used to evaluate film strength and elastic properties. Tests were performed in accordance with ASTM D-882 in the perpendicular direction of film extrusion.

The elastic hysteresis test method consists of two cycles of stretching. The test results are shown in the stress-strain curve in Figure 2. The first cycle at 200% strain is intended to simulate the activation process between the elastic film and the PP nonwoven. The second stretching cycle at 100% strain aims to evaluate the strain and the elastic properties of the elastic film of the diaper. Therefore, the elastic film performance indicator focuses on the second cycle.
The performance indicator and its definition are as follows:
I. Tensile stress at 100% strain (point D in Fig. 2): One of the performance indicators of thin film strength.
II. Elastic recovery stress at 50% unloading stress (point E in Figure 2): Elastic recovery stress can be used as an index of the elastic performance required when a diaper is worn.
III. Permanent slack (point F in Figure 2): ability of an elastic component to resist tensile deformation during the stretching process.

D. Test for evaluating the extensional viscosity of melts:
The Rheotens test was used to measure the melt strength of the material at 170°C, which is a commonly used processing temperature for blown films.

E. Volatile Organic Compound (VOC) Analysis:
Head Space GC was used to test residual VOCs of SIS materials on a fresh production sample.

F. Results and discussion:
I. Mechanical properties of the elastic film:

The comparison of thin film strength performance of VECTOR 4111ND/4258ND and VECTOR 4211ND/4359ND is illustrated by the stress-strain curves in Figure 3 and the tensile properties in Table 2. Since the styrene content and the molecular structure of the new type of VECTOR SIS has been adjusted, the tensile strength performance has been greatly improved.

Additionally, module performance at lower stresses (100%/300%) has also been significantly improved. As shown in Figure 4 and Table 2, the improvements mentioned above confirm the design concept and capabilities of the new high-strength SIS VECTOR 4258ND/4359ND, that is, it can effectively improve the thin film strength and module performance.
II. Elasticity performance of elastic film

Elastic performance indicators can be divided into: The performance of 50% unloading stress, permanent set and hysteresis. These are shown in Figure 5 and Table 3. The new high-strength SIS vector significantly improves the elastic recovery stress of thin films while maintaining low permanent strain.

III. Melt strength and drawability result:
Bubble stability is crucial for blown film processing and is strongly correlated to the melt strength of the material; therefore, higher levels of melt strength generally result in better blown film. When comparing the conventional SIS with the new SIS, VECTOR 4111ND/4258ND and VECTOR 4211ND/4359ND, the Rheotens test results, as shown in Figure 6 and Table 4, show that the high strength VECTOR SIS has a better melt strength and better extensibility than conventional VECTOR SIS. Therefore, the high-strength VECTOR SIS is more suitable for processing blown films.

IV. Reduction of odors in SIS and improvement of the quality of film products:

Head Space GC was used to compare VOCs before and after installation of the new granulator. The results show that VECTOR SIS produced with the new granulation equipment has a 73% reduction in VOCs. Thus, the quality of diapers and masks, whose consumers are sensitive to odors, has been significantly improved.

In response to the new application requirements of thin elastic films, TSRC has developed high strength/high elasticity VECTOR SIS materials which can effectively improve the strength of thin elastic films. Additionally, the melt strength of the material has also been significantly improved, making it very suitable for processing blown films. In terms of odor performance, the newly installed granulation equipment effectively reduces VOC content, greatly minimizes material odor, and improves the quality of film products.

:

1. D. Handlin, Z. Cheng and M. Bérard, ANTEC Tech. Paper. (2015)

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