Materials Discarded BSF and coir fiber were collected from an agricultural farm at Kushtia, Bangladesh. The fibers were extracted by water retting and washed with sodium carbonate and detergents. The properties of the fibers are listed in Table I. Acetic acid (100 wt %), acetic anhydride (99.5 wt %), sodium hydroxide (>99.5 wt %), LDPE (tensile strength = 0.2–0.4 N/mm2 , mp = 1100C, glass-transition temperature = 1250C, density 0.91–0.94 g/cm3 ) were supplied by Merck (Germany). MAPP was purchased from Sigma-Aldrich (USA), and its maleic anhydride content about 8 wt %. The number-average molecular weight and weight-average molecular weight/number-average molecular weight were 3.9 103 and 2.3, respectively.
Fiber Treatment The fiber was cut into pieces approximately 15 cm long. Then, the lignin from fibers were removed by a bleaching operation with a 7 mg/L NaClO2 solution at pH 4 (buffered by CH3COOH and CH3COONa) for 90 min at 353–363 K. The fiber-to-liquor ratio was maintained at 1 : 50. After the reaction was complete, the fiber was washed several times with cold distilled water. Then, the bleached fiber was treated with a 0.2% sodium metabisulfite (Na2S2O5) solution for 15 min and finally washed with distilled water. The untreated BSF was soaked in a 5% NaOH solution in a water bath where the temperature was maintained at 303 K for 10 h and the fiber-to-liquor ratio was 1 : 50. The treated fiber was rinsed several times and left to dry at room temperature. An amount of 10 g of bleached BSF was soaked in glacial acetic acid for 1 h at room temperature. The acid was decanted, and soaking was continued in acetic anhydride (50 mL) containing two drops of concentrated sulfuric acid for 10 min at a fiber-toliquor ratio of 1: 50. The fiber was separated with a Buchner funnel, washed with water, and dried in oven at 323 K for 24 h. The main constituents of BSF and coir fiber were isolated according to a TAPPI standard.27
Fiber Testing The infrared (IR) spectra of the untreated and treated BSF were recorded with a Shimadzu IR-470 spectrophotometer (Shimadzu, Kyoto, Japan) with the KBr pellet technique. A mixture of 5 mg of dried fibers and 200 mg of KBr were pressed into a disk for IR measurement. Composite Preparation Dried BSF (at 5, 10, 20, and 30 wt %) and 5 wt % MAPP were initially mixed thoroughly with LDPE with a single-screw extruder at 433 K. The composites were made with a stainless steel mold measuring 150 x150x 40 mm3 (Lengthx Width x Depth). The releasing agent, PAT 607/PCM, was sprayed onto a laboratory tissue and smeared evenly onto the surface of the mold. The mixture was cut into small pieces and spread uniformly on the surfaces of the molds. Polymer composite sheets were prepared by the hot pressing of the mold at 433+ 5 K for 30 min. The pressure applied ranged from 50 kN, depending on the loading of the reinforcing material. Cooling was done with tap water through the outer area of the heating plates of the Paul–Otto–Weber press machine (China). The specimen were demolded and postcured at 500C for 12 h. The composite sheets were cut for mechanical testing according to an ASTM standard.
Composite Testing The ultimate tensile strength (UTS) and Young’s modulus (YM) values of the BSF composites were measured with an Instron 3366 on the basis of ASTM D 3822-01 and ASTM D 1043-09, respectivly. The gage length and crosshead speed were fixed at 20 mm and 5 mm/min, respectively. Three-point flexural tests of the composites were carried out with the Instron 3366 according to the standard method used for flexural properties (ASTM D 790-98). The speed for the flexural test was set at 5 mm/min. Notched Charpy impact tests (according to ASTM D 6110-97) were carried out with a Universal Impact tester- (cometech) Taiwan, Extruder- Dynisco, Heilbronn, Germany. All of the results were taken as the average value of 10 samples. Scanning electron microscopy (SEM) was used to observe the microstructures and surface morphologies of the untreated BSF, treated BSF, and their composites. The instrument (Philips XL30 SEM Instrument- Germany) was operated with an excitation voltage 30 kV. The samples were coated with 3 nm of gold with a vacuum sputter coater. The thermogravimetric analysis (TGA) of the treated and untreated BSF/LDPE composites was conducted with a thermogravimetric analyzer (model TG 50) supplied by TA Instruments (New Castle, USA). A 20-mg sample of each type of fiber was taken for analysis. The samples were heated steadily at a rate of 20 K/min from 298 to 773 K under a nitrogen atmosphere. To ensure accuracy, the analysis was done two times for each sample.