Influence of the Processes Parameters on the Properties of The ...

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Chapter 4. Experimental Procedures and Protocols for Analyses PLA B PLA Polymer granulates C Ground fine powder Screened powder PLGA A Granulates in <strong>the</strong> chamber Knife mill with water circulation Screening mesh: SS frame & Cloth Overall height = 1-3/4" Depth to cloth: 1-1/4" (32 mm) PLGA Figure 4.1: Polylactide granulates size reduction by knife mill. Few tens <strong>of</strong> grams <strong>of</strong> <strong>the</strong> chosen polymers were introduced in <strong>the</strong> knife mill which was <strong>the</strong>n closed. Cold water was allowed to circulate in <strong>the</strong> mill double jacket. Copolymers such as PLGA 85:15 (PLG , PLG 8531, LG 857 S, … ) are granules, that must be initially pre-ground in batches, in <strong>the</strong> knife mill for a specified time that more than 95% <strong>of</strong> <strong>the</strong> ground material is recovered. Each material was ground in <strong>the</strong> knife mill for alternative time On/Off <strong>of</strong> 60 s to avoid melting or degradation. Times required to recover 95% <strong>of</strong> <strong>the</strong> initial polymer depends on its inherent viscosity. Then, <strong>the</strong> pre-ground product was recovered and sieved according to <strong>the</strong> procedure presented. Waxes used were pre-ground in knife mill but only for 30 s. The wax obtained was very fine that 100% <strong>of</strong> wax removed after pre-grinding passed through 500 mesh sieve. This wax will be utilized latter on as porogen for preparing a mixture with polymer to obtain better scaffolds. 1.1.2 Tumbling Ball Mill Grinding The pre-ground and sieved product was ground in a tumbling ball mill Prolabo ® (cf. Figure 4.2) to several tens <strong>of</strong> micrometers, value <strong>of</strong> <strong>the</strong> size that could not be reached with <strong>the</strong> knife mill. The tumbling ball mill has a grinding chamber with a capacity <strong>of</strong> 5 liters, a height <strong>of</strong> 32 cm and a diameter <strong>of</strong> 27 cm. Sieved polymer powder Balls <strong>of</strong> 9.6, 19.0 and 34 mm diameter B Gloves Stop watch Ceramic lid Closing plate Crushing chamber Balance C D Tumbling ball mill with accessories Metallic rollers Joint seal Speed regulator Electric switch A E Tumbling Ball Mill Description Filler F Sieve Co-ground Material / Mixture Cleaning brush Spatula Ethanol Gloves Figure 4.2: Milling process in tumbling ball mill. - 88 -
Chapter 4. Experimental Procedures and Protocols for Analyses The chamber, a cylindrical shape, is closed with a ceramic lid fixed by a stainless steel bar having two screws. A rubber gasket, placed underneath <strong>the</strong> ceramic jar lid to ensure <strong>the</strong> tightness <strong>of</strong> <strong>the</strong> system. High purity Alumina (Al 2 O 3 ) ceramic balls were used as grinding media. Three diameters (5.5, 9.3, and 17.5 mm) were used to be suitable for all particle sizes. Their respective proportions were respectively set at ¾, ⅛, and ⅛ and in volume. We used a ball filling rate <strong>of</strong> 20% <strong>of</strong> <strong>the</strong> volume <strong>of</strong> <strong>the</strong> chamber. The product filling rate was set at 10% <strong>of</strong> interstitial volume between <strong>the</strong> balls. The process <strong>of</strong> dry grinding begins when one places <strong>the</strong> filled jar on <strong>the</strong> rotating rolls <strong>of</strong> <strong>the</strong> mill. Speed rotation is set at 100 rpm -1 and represents 75% <strong>of</strong> <strong>the</strong> critical speed, to obtain a cataract movement <strong>of</strong> grinding media (cf. Figure 4.3). The critical velocity is <strong>the</strong> rotation speed <strong>of</strong> <strong>the</strong> grinding chamber from which <strong>the</strong> centrifugal force imposes a permanent veneer <strong>of</strong> balls against <strong>the</strong> wall. Figure 4.3: Cataract movement <strong>of</strong> grinding media. Different milling times were applied as per requirement <strong>of</strong> <strong>the</strong> material and experiments. After grinding <strong>the</strong> material is highly electrostatic so ethanol was sprayed in milling chamber to collect <strong>the</strong> fine particles stuck with <strong>the</strong> walls <strong>of</strong> chamber, <strong>the</strong>n <strong>the</strong> whole product was removed from <strong>the</strong> chamber and kept at cool temperature for fur<strong>the</strong>r analyses and uses. 1.2 Sieving <strong>of</strong> Ground Material The product obtained from knife mill or ball mill is powder with particles having a wide range <strong>of</strong> diameter. To make pellets from <strong>the</strong> pre-ground fibres and ground powders, it is necessary to have homogeneous particles. Sieves with different mesh sizes were used (cf. Table 4.1and Figure 4.4). Manual vibration was done for 7 ~ 10 minutes to collect <strong>the</strong> sieved powder. Table 4.1: Sieving mesh for different powder particles. Mesh Size Sieve 125 μm AFNOR NF ISO 3310 250 μm ASTM E11# 400 μm AFNOR NF ISO 3310 500 μm AFNOR NF ISO 3310 600 μm ASTM E11# 800 μm AFNOR NF ISO 3310 The material left on 600 and 800 mesh due to large particle size were knife mill again to reduce <strong>the</strong> paricle size.This material was again sieved by using appropriate sieve. The sieved powder was fur<strong>the</strong>r used for making pellets by using <strong>the</strong> hydraulic press. - 89 -
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Institut National Polytechnique de
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iii Dedicated to My Fathe</
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pleased I was to work with all memb
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Publications and Conferences The wo
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Nomenclature and Abbreviations Abbr
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ρ p Pellet density Splitting (Bra
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Chapter 2 .........................
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6.2.1 Surface Tensions of</
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3.2 Experiments on PLA/Waxes Scaffo
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Figure 4.28: Incremental Intrusion
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