Nanofibril Selulosa Perlakuan Wet Disk Milling dari Bambu Ampel (Bambusa vulgaris var. vulgaris) Terdelignifikasi dan Nanokompositnya

Abstract

Bambu merupakan tanaman berlignoselulosa yang tergolong sebagai jenis cepat tumbuh dengan sebaran, produksi, dan keanekaragaman jenis yang tinggi. Bambu ampel (Bambusa vulgaris var. vulgaris) merupakan salah satu jenis bambu dari genus endemik di Indonesia yang mudah ditemukan terutama di pulau Jawa dan Bali. Bambu ampel mudah tumbuh dan memiliki adaptasi lingkungan yang tinggi. Di sisi lain, informasi karakteristik dasar bambu ampel masih sangat terbatas, sehingga pemanfaatannya masih belum optimal. Oleh karena itu, karakterisasi sifat dasar bambu ampel diperlukan untuk optimalisasi pemanfaatan bambu ampel, sehingga dapat dikembangkan penerapan teknologi yang tepat. Salah satu perkembangan pemanfatan biomassa adalah penerapan teknologi nano yang menjadi tren terbaru terutama untuk produksi nanofibril selulosa sebagai penguat nanokomposit. Karakteristik nanofibril selulosa dipengaruhi salah satunya oleh kadar lignin sisa setelah pra-perlakuan. Lignin sisa memiliki pengaruh terhadap kemudahan proses penguraian, morfologi, dan kristalinitas nanofibril selulosa. Pengaruh lignin dapat bernilai positif ataupun negatif tergantung pada jenis bahan baku, jenis pra-prelakuan, dan kadar yang tersisa pada serat sebelum defibrilasi mekanis. Sementara itu, pengaruh lignin terhadap nanofibril selulosa dari bambu ampel belum diketahui. Berdasarkan permasalahan di atas, penelitian ini bertujuan untuk mengkarakterisasi sifat dasar bambu ampel dan mengevaluasi pengaruh lignin terhadap karakteristik nanofibril selulosa dan nanokomposit bambu ampel. Penelitian ini terdiri atas tiga tahap yang meliputi karakterisasi sifat dasar bambu ampel, preparasi dan karakterisasi nanofibril selulosa bambu ampel, dan preparasi dan karakterisasi nanokomposit berpenguat nanofibril selulosa bambu ampel. Karakterisasi sifat dasar yang dilakukan meliputi anatomi, kristalinitas, dan kadar komponen kimia. Nanofibril selulosa dibuat melalui proses mekanis wet disk milling setelah pra-perlakuan sodium klorit-asam asetat (SC-AA) pada berbagai tingkat delignifikasi. Karakteristik nanofibril selulosa yang diuji meliputi kadar lignin, morfologi, gugus fungsi, dan kristalinitas. Nanokomposit dibuat dengan matriks polivinil alkohol (PVA) dan penguat nanofibril selulosa bambu ampel pada berbagai kadar lignin. Nanokomposit pada berbagai kadar penguat juga dibuat untuk menentukan kadar penguat optimum. Karakteristik nanokomposit yang dievaluasi meliputi sifat fisis, sifat optik, sifat termal, dan sifat mekanis. Hasil penelitian menunjukkan bahwa bambu ampel memiliki tipe ikatan pembuluh III. Karakteristik anatomi dalam batang bambu ampel bervariasi baik pada arah vertikal maupun horizontal. Porsi serat di bagian luar batang bambu lebih tinggi dari bagian dalam dan cenderung turun dari bagian pangkal ke bagian ujung. Porsi vessel dan parenkim lebih tinggi pada bagian dalam dari pada bagian luar. Porsi parenkim cenderung turun dari bagian pangkal ke bagian ujung, sementara porsi vessel cenderung meningkat. Panjang serat di bagian luar secara signifikan lebih tinggi daripada di bagian dalam batang bambu ampel. Pada bagian luar batang bambu, bagian tengah memiliki serat terpanjang dalam arah aksial. Sementara pada bagian dalam, panjang serat menurun dari pangkal ke ujung batang. Lebar kristal dan kristalinitas relatif di bagian dalam lebih rendah daripada di bagian luar batang bambu ampel. Bambu ampel memiliki kadar holoselulosa yang tinggi dan kadar lignin yang rendah. Kadar zat ekstraktif bambu ampel tergolong tinggi. Berdasarkan beberapa karakteristik dasar, bambu ampel potensial dimanfaatkan sebagai bahan baku nanofibril selulosa. Delignifikasi sodium klorit-asam asetat secara efektif mendegradasi lignin. Kadar lignin bambu ampel menurun hingga 83% setelah delignifikasi SC-AA. Nanofibril selulosa bambu ampel tampak semakin memutih dengan meningkatnya delignifikasi. Metode defibrilasi mekanis wet disk milling pada penelitian ini efektif mengekstrak nanofibril selulosa dari bambu ampel. Nanofibril selulosa bambu ampel memiliki ukuran yang cukup panjang dengan diameter rata-rata berkisar pada 9,50 nm hingga 48,83 nm. Diameter nanofibril selulosa bambu ampel menurun dengan meningkatnya delignifikasi. Spektra Fourier Transform Infrared mengkonfirmasi bahwa terdapat terdapat penurunan kadar lignin meskipun masih terdapat residu yang tertinggal pada nanofibril selulosa bambu ampel. Nanofibril selulosa bambu ampel memiliki struktur kristal selulosa I. Kristalinitas dan ukuran atomik kristal menurun dengan meningkatnya pra-perlakuan delignifikasi. Kerapatan nanokomposit dengan penguat nanofibril selulosa bambu ampel lebih rendah dari kerapatan matriks PVA. Penambahan nanofibril selulosa bambu ampel menurunkan daya serap air dan kelarutan nanokomposit. Daya serap air dan kelarutan nanokomposit menurun dengan meningkatnya pra-perlakuan delignifikasi pada nanofibril selulosa bambu ampel. Penambahan nanofibril selulosa menurunkan transparansi nanokomposit. Nanofibril selulosa bambu ampel dengan pra-perlakuan delignifikasi 4 kali memiliki nilai transparansi nanokomposit paling tinggi dibandingkan nanokomposit lainnya. Nanokomposit dengan penguat nanofibril selulosa bambu ampel lebih mudah menerima panas dibandingkan matriks PVA. Nilai laju hantar kalor nanokomposit dengan penguat nanofibril selulosa bambu ampel lebih rendah dari matriks PVA. Kuat tarik dan modulus Young’s nanokomposit meningkat dengan penambahan nanofibril selulosa bambu ampel dan meningkat dengan meningkatnya tingkat pra-perlakuan delignifikasi dari 1 kali hingga 4 kali. Elongasi patah nanokomposit menurun drastis dengan penambahan nanofibril selulosa. Sifat mekanis nanokomposit secara efektif mulai meningkatkan setelah penambahan nanofibril selulosa bambu ampel sebanyak 5%.

Bamboo is a lignocellulosic plant that is classified as a fast-growing species with high distribution, production, and species diversity. Ampel bamboo (Bambusa vulgaris var. vulgaris) is a bamboo species from an endemic genus in Indonesia that is easy to find, especially on the islands of Java and Bali. Ampel bamboo is easy to grow and has high environmental adaptability. On the other hand, information on the basic characteristics of ampel bamboo is still very limited, so that the utilization of ampel bamboo is still not optimal. Therefore, characterization of the basic properties of ampel bamboo is needed to optimize the use of ampel bamboo, so that the application of appropriate technology can be developed. One of the developments in the utilization of biomass is the application of nanotechnology which is the latest trend, especially for the production of cellulose nanofibrils as nanocomposite reinforcement. Characteristics of cellulose nanofibrils is influenced by the residual lignin content after pre-treatment. Residual lignin has an influence on the ease of defibrillation process, morphology, and crystallinity of cellulose nanofibrils. The effect of lignin can be positive or negative depending on the type of raw material, the type of pre-treatment, and the content remaining in the fiber before mechanical defibrillation. Meanwhile, the effect of lignin on cellulose nanofibrils from ampel bamboo is not known yet. Based on the problems above, this study aims to characterize the basic properties of ampel bamboo and evaluate the effect of lignin on the characteristics of cellulose nanofibrils and nanocomposites of ampel bamboo. This research consisted of three stages which included characterization of the basic properties of ampel bamboo, preparation and characterization of ampel bamboo cellulose nanofibrils, and preparation and characterization of ampel bamboo cellulose nanofibrils reinforced nanocomposite. Characterization of the basic properties carried out included anatomy, crystallinity, and chemical components content. Cellulose nanofibrils were made by mechanical wet disk milling after pre-treatment with sodium chlorite-acetic acid (SC-AA) at various levels of delignification. The characteristics of cellulose nanofibrils tested included lignin content, morphology, functional groups, and crystallinity. The nanocomposites were made with a matrix of polyvinyl alcohol (PVA) and ampel bamboo cellulose nanofibril reinforcement at various lignin content. Nanocomposites at various reinforcing content were also made to determine the optimum reinforcement levels. The evaluation of nanocomposite characteristics include physical properties, optical properties, thermal properties, and mechanical properties. The results showed that ampel bamboo had vascular bundle type III. Anatomical characteristics in ampel bamboo stems were vary in both vertical and horizontal directions. The fiber portion on the outer of the bamboo stem is higher than the inner side and tends to decrease from the base to the tip. Vessel and parenchyma portions are higher on the inner than on the outer side. The parenchyma portion tends to decrease from the base to the tip, while the vessel portion tends to increase. The fiber length on the outer was significantly higher than on the inner side of ampel bamboo stems. On the outer of the bamboo stem, the middle has the longest fibers in the axial direction. While on the inner side, the fiber length decreases from the base to the tip of the stem. The crystal width and relative crystallinity on the inner were lower than on the outer side of ampel bamboo stems. Ampel bamboo has high holocellulose content and low lignin content. The extractive content of ampel bamboo is relatively high. Based on several basic characteristics, ampel bamboo has the potential to be used as raw material for cellulose nanofibrils. The delignification of sodium chlorite-acetic acid effectively degrades lignin. The lignin content of ampel bamboo decreased to 83% after SC-AA delignification. ampel bamboo cellulose nanofibrils appear to be whiter with increasing delignification. The wet disk milling mechanical defibrillation method in this study was effective in extracting cellulose nanofibrils from ampel bamboo. Ampel bamboo cellulose nanofibrils have a fairly long size with an average diameter ranging from 9.50 nm to 48.83 nm. The diameter of ampel bamboo cellulose nanofibrils decreased with increasing delignification. The Fourier Transform Infrared spectra confirmed that there was a decrease in lignin content although there were still residues left on the ampel bamboo cellulose nanofibrils. The ampel bamboo cellulose nanofibrils had a cellulose I crystal structure. The crystallinity and atomic size of the crystals decreased with increasing delignification pre-treatment. The density of nanocomposites with ampel bamboo cellulose nanofibrils was lower than that of the PVA matrix. The addition of ampel bamboo cellulose nanofibrils decreased water absorption and nanocomposite solubility. The water absorption and solubility of nanocomposites decreased with increasing delignification pre-treatment on ampel bamboo cellulose nanofibrils. The addition of cellulose nanofibrils decreased the transparency of the nanocomposite. Ampel bamboo cellulose nanofibrils with 4 times delignification pre-treatment had the highest nanocomposite transparency value compared to other nanocomposites. Nanocomposites with bamboo ampel cellulose nanofibril reinforcement are more receptive to heat than PVA matrix. The value of the heat conduction rate of nanocomposite with ampel bamboo cellulose nanofibril reinforcement is lower than that of the PVA matrix. Tensile strength and Young's modulus of nanocomposite increased with the addition of ampel bamboo cellulose nanofibrils and increased with increasing delignification pre-treatment level from 1 to 4 times. The elongation at break of nanocomposite decreased drastically with the addition of cellulose nanofibrils. The mechanical properties of the nanocomposite effectively started to improve after the addition of 5% ampel bamboo cellulose nanofibrils.