Judul: Modification of cassava waste pulp to hydrophilic products by oxidation-grafting
Abstrak: Cassava waste pulp (CWP) from tapioca industrial byproducts present in large numbers. Native starch in CWP has the high potential to raw material, but it possess some undesirable properties limiting its use in industrial applications. These limitations make the research on native starch increased through modification by physically, chemically or enzymatically and resulting in products with a higher added value. The purpose of this study to obtain optimum oxidation conditions of oxidized cassava waste pulp (OCWP) through determining the factors that significantly affect the oxidation process and synthesize hydrogel base OCWP with a character of saline-tolerant. The hydrogels from this study is expected to be a superabsorbent and into the future promising product for agriculture and personal care industries. Potential factors that must be considered in the oxidation process of CWP are temperature, pH, oxidation time, the amount of oxidant and catalyst. The experimental results of the response surface methodology showed the factors that have an important influence on the optimum conditions of oxidation are 78.335 °C temperature, 4.301 ml catalyst and oxidation time of 83.613 minutes. The OCWP was used as the main framework of grafting. Oxidation of CWP produce carbonyl (C=O) and carboxyl (-COO) group which will make it more hydrophilic. Furthermore, the OCWP grafting with acrylic acid (AA) and acrylamide (AM) monomer was optimized for the production of hydrogels. The characterization of oxidation product and hydrogels through the analysis of the IR spectrum and SEM photos. The state of absorbing water (swelling) is the primary parameter of a hydrogel as a candidate of absorbent material. The average of water absorption the OCWP hydrogels is two times higher than the CWP hydrogels. However, both of hydrogel types which are synthesized to be a superabsorbent because it can absorb water up to more than 100 times the dry weight. The Hydrogel swelling capacity in salt solution is significantly reduced compared to swelling in distilled water. However, the effect of NaCl concentration on water absorption capacity for the OCWP-AA and CWP-AM hydrogel has been constantly respectively above of 0.173 M and 0.296 M compared with CWP-AA hydrogel absorption was continuously decreased above of 0.34 M NaCl concentrations. The absorption average difference in the NaCl solution showed the OCWP-AA and OCWP-AM hydrogel has swelling respectively 26 and 12.5 times greater than the CWP-AA hydrogel. Thus, the hydrogel of CWP after oxidation tolerant of saline solution compared with the hydrogel of CWP before oxidation.
Keyword: cassava waste pulp, grafting, hydrogels, oxidation, saline-tolerant

Judul: Sintesis Superabsorben melalui Kopolimerisasi Pencangkokan Asam Akrilat pada Onggok Dialdehida
Abstrak: Cassava waste pulp (onggok) is a residual pulp obtained from starch industry. The purpose of this study is to modify the pulp through oxidation with NaIO4 followed by grafting and crosslinking copolymerization to obtain superabsorbent polymer (SAP). The carbonyl content measurement was utilized to determine the optimum condition for oxidation. Oxidation with 0.05 M NaIO4 for 1 hour and subsequent acetone washing solution gave the best result. Grafting and crosslinking of acrylic acid on the pulp backbone were performed with N,N’- methylene-bis-acrylamide as crosslinker and ammonium peroxidisulfate as the initiator. The synthesis was carried out at 70–75 ºC for 3 hours, then the water absorptive capacity of the copolymer products were determined. Water absorptive capacity of SAP was 893.22 g/g in 24 hours. The maximum absorptive capacity of SAP in solutions with pH ranging from 2 to 11 was 915.26 g/g at pH 9, whereas the maximum absorptive capacity in salt solutions were obtained at 0.01 M NaCl, namely 137.42 g/g.
Keyword: absorptive capacity, acrylic acid, cassava, oxidation, superabsorbent

Judul: Teknik penentuan posisi bintang berdasarkan pelat foto overlapping
Abstrak: Bintang adalah salah satu objek langit yang menarik untuk diamati. Untuk itu, pengetahuan tentang posisi bintang sangat diperlukan. Posisi bintang di langit dapat dihitung melalui foto bintang. Fotografi astronomi atau astrometri merupakan ilmu yang mempelajari metode untuk menentukan posisi bendabenda langit seperti bintang berdasarkan pelat foto (Kamp, 1967). Sebuah pelat foto berisi citra bintang-bintang yang sudah diketahui posisinya berdasarkan katalog dan citra bintang-bintang yang belum diketahui posisinya. Posisi bintang yang ada di katalog dinyatakan dengan (a,3). Bintang yang belum diketahui posisinya lebih banyak jumlahnya daripada bintang yang sudah diketahui posisinya. Citra bintang pada pelat foto berupa sebuah titik dalam bentuk tetap. Posisinya pada pelat merupakan hasil pengukuran pada bidang kartesius dan dinyatakan dengan (1;,fl). Hasil pengukuran tersebut kemudian direduksi menjadi koordinat terukur (x,y). Hubungan antara (a,3) dan (x,y) didekati dengan sebuah deret dengan konstanta-konsranta deret merupakan konstanta pelat. Nilai konstanta pelat diperoleh dengan menggabungkan hasil pengukuran posisi bintang pada masing-masing pelat menjadi sebuah persamaan normal (Jefferys, 1963). Hasil akhir dari gugus persamaan normal tersebut dijabarkan dalam bentuk nOlasi matriks partisi dan berupa sebuah sistem persamaan linier Ax = b di mana A adalah matriks jarang, dan x merupakan konstanta pelar yang akan dicari nilainya. Untuk menyelesaikan sistem persamaan linier terse but digunakan metode transformasi given. Konstanta pelat yang sudah diperoleh dengan menyelesaikan sistem persamaan linier di atas, kemudian disubtitusi ke sebuah persamaan untuk memperoleh posisi bintang yang tidak tercantum dalam katalog. .
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