Crystallization Kinetics Study of Impact Polypropylene Copolymer with Kenaf as Nucleating Agent and Reinforcement
Corresponding email: fajar@metal.ui.ac.id
Published at : 30 Oct 2019
Volume : IJtech
Vol 10, No 5 (2019)
DOI : https://doi.org/10.14716/ijtech.v10i5.2267
Fatriansyah, J.F., Barmaki, M.J.Y., Lailani, R.Chalid, M., 2019. Crystallization Kinetics Study of Impact Polypropylene Copolymer with Kenaf as Nucleating Agent and Reinforcement. International Journal of Technology. Volume 10(5), pp. 999-1009
| Jaka Fajar Fatriansyah | Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
| Muhammad Joshua Yuriansyah Barmaki | Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
| Rahma Lailani | Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
| Mochamad Chalid | Department of Metallurgical and Materials Engineering, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia |
Impact Polypropylene Copolymer (IPC) is an
material which combines properties of isotactic Polypropylene (iPP) and its own
high impact toughness. However, the crystallization kinetics might be lower
than iPP, which may affect the manufacturing cycles. Kenaf was used as the
addition in IPC, in which kenaf acts as a nucleating agent as well as reinforcement
for IPC. Kenaf was alkalized with NaOH 6 v.v% for about 8 hours to remove the
dirt on the surface and to reduce lignin, which contributed polarity to kenaf.
The alkalization improved the compatibility of kenaf fiber with IPC. The
crystallization kinetics study was conducted by employing the Avrami model to
Differential scanning calorimetry data in order to obtain half-time, Avrami
index (morphology parameter) and Avrami crystallization kinetics. The addition
of 5 wt.% kenaf was found to be an optimum concentration to improve
crystallization kinetics. The addition of more than 5 wt.% kenaf (15 wt.% and
20 wt.%) did not improve crystallization kinetics which may be due to the
agglomeration, thus preventing efficient heat transfer between nucleating seeds
and the matrix. The connection between crystallization kinetics and mechanical
properties was also established for the IPC+ kenaf system.
Crystallization kinetics; Impact polypropylene copolymer; Kenaf fiber; Nucleating agent; Polymer reinforcement
Impact Polypropylene Copolymer (IPC) is a unique plastic material,
combining properties of isotactic Polypropylene (iPP) which has a good heat
resistance (insulator), good toughness (Chen et al., 2009), good
manufacturability (Karger-Kocsis et al., 1997), and most important, the
superior property of high impact toughness (Michael, 1991). Because of these
useful properties, IPC is widely used in many applications such as in
packaging, household appliances, automotive parts and even military uses
(Hongjun et al., 1999). IPC is commonly produced from homopolymerization of
Propylene and followed by copolymerization of propylene and ethylene. Thermal
behavior of plastics greatly affects manufacturing process and properties of
the product. Thermal behavior is related to the kinetics of crystallization
(Chalid et al., 2017; Chalid et al., 2018). Crystallization kinetics of IPC may
be lower in comparison with iPP due to the structure of ethylene. This may
affect cycle time in the manufacturing process, for example, due to the longer
crystallization time. One of the methods
to improve the crystallization of kinetic properties is the addition of a
nucleating agent (Tolinski, 2009).
Usually natural based fiber is used as a reinforcement to improve mechanical properties of plastic composites due to its advantages such as: low density, availability, degradability as well as less abrasive and good insulator. Natural fibers can be classified into three types: fiber from plants (cellulose or lignocellulose), fiber from animals (protein) and mineral fibers (Akil et al., 2011). Examples of plant based are flax, jute, ramie, kenaf, sisal, bamboo, wheat, maize, barley and sago (Abral et al., 2012). The use of natural based fiber as a nucleating agent in plastics has increasingly attracted some researchers. However, some researchers use natural based fibers as nucleating agents as well. Fundador et al. (2012) used xylan ester from hemicellulose as a nucleating agent for polylactic acid (PLA). Guo et al. (2015) used natural protein fiber as a nucleating agent for iPP. They showed that the use of other natural fiber resources as a nucleating agent is possible. Yuanita et al. (2015) used Arenga pinnata “ijuk” fiber in PLA nucleating agent and Prabowo et al. (2017) used similar ijuk to modify crystallinity of the iPP composite.
Kenaf
(Hibiscus cannabinus), a plant based natural fiber, has high tensile strength
(930 MPa) as well as low density (Akil et al., 2011). This high tensile
strength makes kenaf suitable as a reinforcement. However, in order to be
properly used as a nucleating agent, the interface between kenaf and IPC should
be compatible with each other. It is well known that the non-polar IPC will be
incompatible with polar natural fibers: this is the case with kenaf (Spoljaric et al., 2009). One of the methods used to reduce
the polarity of kenaf is alkaline treatment (alkalization) (Akhtar et al.,
2016). The alkalization process on fiber may reduce the polarity of fiber by
removing its lignin which donors the polarity property in fiber. Another study
of alkali treatment (alkalization) to improve the capability of ijuk to be
compatible for reinforcement and/or nucleating agent in polymer was conducted
by Chalid and Prabowo (2015) by using
NaOH. They found that the crystallinity, which is somehow related to the
interface or compatibility with polymer, of ijuk increases after alkalization.
The objective of this study is to study the use of NaOH alkalized kenaf as a
nucleating agent as well as reinforcement for IPC. We expect that kenaf will
improve IPC crystallization kinetics, which will be analyzed by means of the
Avrami crystallization theory. In addition, in this paper, we attempt to
establish the relation between crystallization kinetics and mechanical strength
(the use of kenaf as reinforcement) through the experimental results.
The alkalization of kenaf by NaOH was partially successful at removing dirt
on the surface of kenaf and reduced lignin, which was investigated by means of
FESEM and FTIR. The reduction of lignin decreased the polarity of kenaf and
made it more compatible with IPC. The addition of kenaf at concentration of 5
wt.% increased the crystallization kinetics in the following ways: rate of
crystallization (crystallization time) parameter, Avrami crystallization
kinetic parameter and reduced Avrami index. In general, the addition of kenaf
at concentration of 5 wt. % improves crystal growth dynamics and morphology
(crystal growth in one dimension). However, further addition of kenaf does not
improve growth dynamics and morphology. This phenomenon could be caused by
agglomeration and thus preventing effective heat transfer between crystal seeds
and the matrix. In addition, the connection between crystal growth dynamics and
mechanical strength (tensile strength) has been successfully established
through crystallization kinetics and mechanical test results. It is shown that
better crystal growth dynamics yields better mechanical strength in the IPC+
kenaf system.
This work was
supported by Universitas Indonesia through HIBAH PITTA A 2019 under contract
number NKB-0464/UN2.R3.1/HKP.05.00/2019.
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