Sains Malaysiana 49(9)(2020): 2169-2185

http://dx.doi.org/10.17576/jsm-2020-4909-15

Non- Isothermal Crystallization Kinetics of Poly(Lactic Acid)/Kenaf Fiber Composites

(Kinetik Penghabluran bukan Isoterma Komposit Poli(Laktik Asid)/Serat Kenaf)

ADIBAH BORHAN & RAZAINA MAT TAIB*

School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Pulau Pinang, Malaysia

Received: 15 October 2019/Accepted: 8 May 2020

Abstract

The non-isothermal crystallization behavior of poly(lactic acid) (PLA)/kenaf fiber (KF) composites was investigated using differential scanning calorimetry (DSC) at different cooling rates (1, 2.5, 5, and 7.5 °C/min) with various KF sizes from 25 to 300 µm. The modified Avrami, Ozawa, and Mo methods were applied to study the non-isothermal crystallization kinetics of neat PLA and PLA/KF composites. It was found that KF size of 80-106 µm acts as nucleating agent during non-isothermal crystallization of PLA/KF composites since the values of half-time of crystallization (t_1/2) of PLA80 were the fastest as compared to neat PLA and other PLA/KF composites at a given cooling rate. The Avrami-Jeziorny crystallization rate constant (Z_c) increased upon increased of cooling rates for both neat PLA and PLA/KF composites indicating the improvement in crystallization. However, only the Z_c values for PLA80 were faster than PLA/KF composites but slower than neat PLA at a certain cooling rate. The Ozawa method did not apply satisfactorily for both neat PLA and PLA/KF composites. Meanwhile, the results showed that the Mo method can be successfully applied by providing a good fitting for all cooling rates of neat PLA and PLA/KF composites. The Kissinger activation energy (ΔE) of PLA80 recorded the lowest value indicating the size of KF between 80-106 µm accelerated the non-crystallization of PLA.

Keywords: Differential scanning calorimetry; kenaf fiber; non-isothermal crystallization; poly(lactic acid)

Abstrak

Tingkah laku penghabluran bukan isoterma komposit poli(laktik asid) (PLA)/serat kenaf (KF) dikaji dengan menggunakan kalorimetri pengimbasan perbezaan (DSC) pada kadar pendinginan yang berbeza (1, 2.5, 5 dan 7.5 °C/min) dalam pelbagai saiz KF daripada 25 hingga 300 μm. Kaedah Avrami diubah suai, Ozawa, dan Mo digunakan untuk mengkaji kinetik penghabluran bukan isoterma PLA tulen dan komposit PLA/KF. Telah didapati bahawa saiz KF 80-106 μm bertindak sebagai agen nukleasi semasa penghabluran bukan isoterma komposit PLA/KF kerana nilai-nilai separuh masa penghabluran (t_1/2) PLA80 adalah terpantas berbanding dengan PLA tulen dan PLA/KF komposit mengikut kadar pendinginan yang diberikan. Kadar tetap penghabluran Avrami-Jeziorny (Z_c) meningkat apabila peningkatan kadar pendinginan untuk kedua-dua PLA tulen dan komposit PLA/KF menunjukkan peningkatan dalam penghabluran. Walau bagaimanapun, nilai Z_c untuk PLA80 lebih cepat daripada komposit PLA/KF tetapi lebih perlahan daripada PLA tulen pada kadar pendinginan tertentu. Kaedah Ozawa tidak menunjukkan penerapan yang baik untuk PLA tulen dan komposit PLA/KF. Sementara itu, keputusan menunjukkan bahawa kaedah Mo dapat diterapkan dengan berkesan dengan menunjukkan garisan yang kemas bagi semua kadar pendingin PLA tulen dan komposit PLA/KF. Pengaktifan Kissinger (ΔE) PLA80 mencatatkan nilai terendah yang menunjukkan saiz KF antara 80-106 µm mempercepatkan penghabluran semula PLA.

Kata kunci: Kalorimetri pengimbasan perbezaan; penghabluran bukan isoterma; poli(laktik asid); serat kenaf

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*Corresponding author; email: razaina@usm.my