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Abstrak :
ABSTRAK
Dalam studi ini, perilaku dekomposisi termal dan kinetika asam polilaktat (PLA) dan komposit PLA/kenaf diselidiki menggunakan analisis termogravimetri (TGA), untuk menentukan pengaruh penambahan serat kenaf pada dekomposisi termal dan karakteristik kristalisasi. Studi kinektika dilakukan dengan menggunakan model Nakamura yang merupakan model Avrami yang dimodifikasi. Model ini digunakan untuk menentukan indeks Avrami dan parameter kinetik dari PLA dan komposit PLA/kenaf. Hasil penelitian menunjukkan bahwa penambahan serat kenaf ke dalam PLA dapat meningkatkan ketahanan termal, menurunkan indeks Avrami, mempercepat proses kristalisasi, dan mempercepat waktu paruh kristalisasi, serta meningkatkan kekuatannya. UKCC merupakan komposit PLA/kenaf dengan ketahanan termal yang terbaik dan memiliki kecepatan kristalisasi tertinggi pada sistem non-isotermal dengan nilai 𝐾𝑁𝑎𝑘(𝑇) sebesar 1,4114×10−3, serta nilai waktu paruh tercepat, yaitu 601,503 s, terjadi pengurangan waktu hingga 24,37%. TKCC merupakan komposit PLA/kenaf dengan nilai indeks Avrami yang paling mendekati nilai 2, yaitu 2,0618 dan memiliki kecepatan kristalisasi tertinggi pada sistem isotermal dengan nilai 𝐾𝑡 sebesar 4,69311×10−7. Serat dari inti batang kenaf dapat menjadi pilihan terbaik untuk dicampurkan ke dalam PLA murni sebagai komposit PLA/kenaf. Alkalinisasi dapat menjadi pilihan jika lebih menginginkan kekuatan material yang lebih baik dibandingkan dengan waktu proses kristalisasi yang cepat.

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ABSTRACT
In this study, the thermal decomposition behaviour and kinetics of polylactic acid (PLA) and PLA/kenaf composites were investigated using thermogravimetric analysis (TGA), to determine the effect of kenaf fibre addition on its thermal decomposition and crystallization characteristics. The kinectics study was conducted using Nakamura model which is a modified Avrami model. The model is used to determine the Avrami index and kinetic parameters of PLA and PLA/kenaf composite. The results show that the addition of kenaf fibre into the PLA increase thermal resistance, decrease the Avrami index, speed up the crystallization process, speed up the half-time of crystallization, and increase the strength. UKCC is a PLA/kenaf composite with the best thermal resistance and has the highest crystallization speed in non-isothermal systems with KNak(T) value is 1,4114×10−3, and the fastest half-time value is 601,503 s, occurs time reduction of up to 24,37%. TKCC is a PLA/kenaf composite with an Avrami index value closest to 2, namely 2,0618 and has the highest crystallization speed in an isothermal system with Kt value is 4,69311×10−7. Kenaf core fibre can be the best choice for mixing into PLA as a PLA/kenaf composite. Alkalinization can be optional for the better material strength compared to the fast crystallization time.

Abstrak :
Enzyme activity can be used as a peat decomposition indicator in the oil palm rhizosphere of peatlands. Oil palm plantation management requires fertilization in the rhizosphere to provide nutrients for oil palm growth. The state of total nutrient in the rhizosphere can influence enzyme activity. This research aimed to study enzyme activity in relationship to nutrients in the oil palm rhizosphere of peatlands. Using the explorative method in Riau’s tropical peatlands, an oil palm plantation was chosen as a location for the main sites, and a degraded forest as well as a shrubland were chosen as comparison sites. In the oil palm plantation, peat samples were taken from peats adhering to oil palm roots at the peat depths of 0‒25 and 25‒50 cm and at distances of 0‒1, 1‒2, 2‒3, and 3‒4 m from the trees. In the degraded forest and shrub, t samples were taken from selected plant roots at the depths of 0-25 and 25-50 cm. The triplicate peat samples were then composited for an analysis of enzyme activity and total nutrient content. Results showed that enzyme (urease, phosphatase, β-glucosidase, and laccase) activity in the oil palm rhizosphere decreased as the distance from trees and the depth of rhizosphere increased. The decline in enzyme activity was caused by a low peat pH and an increased water content as well as organic carbon content. Enzyme activity increased with increasing oil palm age and ash content. Total K and Zn contents showed no correlation with enzyme activities. However, total Ca and Mg contents showed positive correlation only with β-glucosidase activity. Total Fe and Cu contents showed significantly negative correlation with enzyme activities (urease, phosphatase, β-glucosidase, and laccase). Enzyme activity in the rhizosphere of the degraded forest and shrubs were mostly lower than in the oil palm rhizosphere.