The Physical And Thermal Properties Of Modified Rotational Molding Grade Silane Cross–Linked Polyethylene Compound

Abstract

Uji kaji ini dijalankan untuk mengkaji sifat fizikal dan terma bagi formulasi campuran polietilina berangkai silang gred acuan putaran berasaskan kebolehprosesan. High Density Polyethylene (HDPE) gred acuan putaran dicampur dengan pelbagai komposisi HDPE dan Low Density Polyethylene (LDPE) menggunakan penyemperit skru pendua. Indeks Aliran Lebur (MI) campuran dikaji berasaskan ASTM D 1238. Komposisi campuran tersebut disambung silang secara kimia dengan agen penyambung silang silane menggunakan 'two roll mill’. Kemudian sambung silang lembapan dilakukan di dalam water bath selama 4 jam dan 8 jam. Kandungan gel diukur mengikut ASTM D 2765 bagi menentukan darjah penyambungan silang. Bagi analisis terma,hanya sampel yang disambung silang dengan 2.0 phr agen penyambung silang silane dikaji dengan Kalorimetri Pengimbasan Pembeza (DSC) berdasarkan ASTM 3417. Ujian kestabilan terma bagi XLPE silane dilakukan dengan menggunakan Penganalisa Termogravimetri (TGA) mengikut ASTM D 3850. Keputusan bagi Indeks Aliran Lebur (MI) menunjukkan campuran antara HDPE gred acuan putaran dengan HDPE lebih tinggi berbanding LDPE, dengan itu menambahbaik kebolehprosesan bahan. Ketumpatan campuran antara HDPE gred acuan putaran HDPE meningkat sedikit manakala campuran dengan LDPE menurun sedikit. Sampel yang dicampur dengan HDPE tidak menunjukkan perubahan bagi suhu lebur, Tm manakala darjah penghabluran, Xc, mengalami penurunan. Sampel campuran dengan LDPE pula, Tm dan Xc menurun dengan bertambahnya komposisi LDPE menunjuk kepada kebolehprosesan yang lebih baik. Kandungan gel meningkat dengan penambahan kepekatan silane dan tidak bergantung kepada komposisi campuran. Masa pengawetan yang lebih panjang menghasilkan nilai gel yang tinggi. Kestabilan terma PE yang dirangkai silang lebih tinggi berbanding HDPE yang tidak dirangkai silang. Oleh yang demikian, penyambungan silang secara silane menambahkan kestabilan campuran. Kata kunci: HDPE rangkai silang silane, acuan putaran, sifat fizikal, sifat terma dan kebolehprosesan This study is aimed at investigating the physical and thermal properties of the modified rotational molding grade cross-linked polyethylene compound with respect to process ability. Rotational molding grade High Density Polyethylene (HDPE) was blended at various compositions with HDPE and Low Density Polyethylene (LDPE) using twin screw extruder. The melt index of the blends was studied according to ASTM D 1238. The blended compositions were chemically cross-linked with various amount of silane cross-linking agent using two roll-mill. Water curing was then undertaken at 100C in water bath for 4 and 8 hours. Gel content was measured according to ASTM D 2765 to determine the degree of cross-linking. For thermal analysis, only samples crosslinked with 2.0 phr silane cross-linking agent were investigated on the Differential Scanning Calorimetry (DSC) according to ASTM D 3417. The thermal stability test of the silane Crosslinkable Polyethylene (XLPE) was performed by Thermogravimetric Analyzer (TGA) according to ASTM D 3850. Results on melt index (MI) indicated that the rotational molding grade HDPE blended with HDPE showed higher MI compared to that with LDPE thus improved process ability. The density of rotational molding grade HDPE with HDPE was slightly increased whereas that blended with LDPE was slightly decreased. Samples blended with HDPE, melting temperature, Tm, barely changed and degree of crystallinity, Xc, decreased with compositions. Samples with LDPE Tm and Xc decreased with compositions thus improved process ability. As the silane concentrations increased, the gel content after curing was also increased but independent of compositions. Longer curing time resulted in higher gel content. Thermal stability of the crosslinked HDPE was higher than the uncross-linked HDPE, thus silane cross-linking help to stabilize the blends. Key words: Silane cross–linked high density polyethylene, rotational molding, thermal properties, physical properties and process ability