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

Chapter 2.
<strong>Processes</strong> to Manufacture Foams and to Functionalize <strong>the</strong> Surface
Figure 2.21: Schematic <strong>of</strong> <strong>the</strong> phenomenon <strong>of</strong> fragmentation in <strong>the</strong> co-grinding.
The fine particles <strong>of</strong> component B will have a tendency, because <strong>of</strong> interparticle forces to stick to
larger particles. More continuous grinding, <strong>the</strong> more phenomenon is growing. Different stages <strong>of</strong>
agglomeration will be encountered: <strong>the</strong> simple bonding between two or more particles, <strong>the</strong>n <strong>the</strong> stage <strong>of</strong>
coating particles and finally <strong>the</strong> agglomeration stage <strong>of</strong> particles toge<strong>the</strong>r. The type <strong>of</strong> observed phenomenon
will depend, among across <strong>the</strong> duration <strong>of</strong> <strong>the</strong> operation and products affinity. Figure 2.22 shows changes in
<strong>the</strong> different stages <strong>of</strong> agglomeration during <strong>the</strong> co-grinding.
Figure 2.22: Different stages <strong>of</strong> agglomeration during <strong>the</strong> co-grinding: (a) adhesion, (b) coating and (c)
agglomeration.
This technique was developed accidentally in 1968 to manufacture metal alloys. The metals were
co-milled in a strongly energetic ball mill, producing a fine powder as an alternative mechanism <strong>of</strong> fractures
and cold welds. Gilman and Benjamin [1983] were interested in <strong>the</strong> mechanisms <strong>of</strong> alloys formation and
have applied <strong>the</strong> technique to a large number <strong>of</strong> metallic elements to create a data library. Currently in <strong>the</strong>
process <strong>of</strong> mechanical alloying is no longer reserved solely for metals. Indeed, Yenikolopyan [1988] studied
<strong>the</strong> system polypropylene / polyethylene low density in a ball mill. The co-grinding increases <strong>the</strong> surface
specific powder consisting <strong>of</strong> small clusters whose size varies between 100 nm and few microns. An X-ray
analysis showed that <strong>the</strong> crystallinity <strong>of</strong> <strong>the</strong> mixture increases with time <strong>of</strong> co-grinding. The use <strong>of</strong> milling
for <strong>the</strong> formation <strong>of</strong> mixed polymer can thus produce very homogeneous powders. O<strong>the</strong>r studies by Pan and
Shaw [1994, 1995] showed that both polymers semi-crystalline and <strong>the</strong>rmoplastic (polyamid 6,6 polymer
and high density) can be co-ground as a fine powder using a vibrating ball mill operating in <strong>the</strong> dry process.
The mechanical alloying to produce a material with one hand, a more homogeneous charge consisting <strong>of</strong>
grains less than 1 micron and <strong>the</strong> o<strong>the</strong>r improved mechanical properties. Never<strong>the</strong>less, this study was
conducted in a small mill (a few tens <strong>of</strong> millilitres) whose dimensions are difficult to extrapolate, by
technological complexity resulting from <strong>the</strong> vibrating system. Few studies have examined <strong>the</strong> production <strong>of</strong>
composite materials by co-grinding and even on co-grinding in general. Aspects <strong>of</strong> training methods and
mechanisms <strong>of</strong> materials have mostly been obscured in favour <strong>of</strong> <strong>the</strong> characterization <strong>of</strong> <strong>the</strong> materials
obtained. A similar study was done Zapata-Massot [2004] by Zapata for brittle polymer Poly vinyle acetate
and a mineral filler calcium carbonate to improve <strong>the</strong> properties <strong>of</strong> <strong>the</strong> composite formed.
In ano<strong>the</strong>r study by Seyni [2009] shows <strong>the</strong> interest to implement vegetable biodegradable filler in
composite materials. The incorporation <strong>of</strong> starch as filler in <strong>the</strong> polymeric matrix was carried out by cogrinding,
process supporting <strong>the</strong> dispersion <strong>of</strong> a component in <strong>the</strong> o<strong>the</strong>r as well as <strong>the</strong> homogeneity <strong>of</strong> <strong>the</strong>
composite properties. Co-grinding makes it possible to improve <strong>the</strong> mechanical and <strong>the</strong> optical properties, as
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