Compounding Processes
-
Upload
ghiska-ramahdita -
Category
Documents
-
view
241 -
download
1
Transcript of Compounding Processes
-
7/31/2019 Compounding Processes
1/22
-
7/31/2019 Compounding Processes
2/22
Blending
Stirring together/blending of a number of solids, e.g.polypropylene
powder, pigment, antioxidant, etc.
The results is a mixture of powders; the indiv idual powder remain and
can be separated (in principle)
Compounding
Involves more intimate dispersion of the additives into the polymeric
matrix
It requires;
A physical change in the component High shear force to bring about the change
The polymer to be in the molted or rubbery state during mixing
Some Processes and Machine (Blending)
Vary from the simplest to sophisticated high speed
machine
The simplest- is to tumble together dry ingredients, e.g.
using a twin-drum tumbler
Twin-drum tumbler
-
7/31/2019 Compounding Processes
3/22
Ribbon-blender
A tumbling action takes place
The chamber is stationary and the ribbons rotate
constantly scooping the material from the outside to
the centre
Some Processes and Machine (Blending)
Ribbon blender
High speed mixer
More sophisticated & rapid machine for blending
Widely used for PVC dry blends, drying, incorporated pigments,
antioxidant, etc.
Run at several thousand rpm, and form a circulating powders
which becomes heated by friction (150-200C)
Mixing tank can be single wall or jacketted for temp. control
Some Processes and Machine (Blending)
High Speed MixerMixing tank
-
7/31/2019 Compounding Processes
4/22
Dough Moulding Compound
Dough-like blend, e.g. DMC are made in Z-blade (The name
comes from the shape of the mixing blade)
The mixer itself comprises twin stainless steel bowls in each of
which is a mixing blade. The blades rotate in opposite directions
(and rarely at different speeds).
Some Processes and Machine (Blending)
Ball Mill Comprises of cylindrical vessel containing large number of steel or
ceramic balls
It rotates, the balls tumble inside together with the powder
Agglomerates of powder are broken down by the grinding action of
the tumbling balls
Some Processes and Machine (Blending)
Ball Mill
-
7/31/2019 Compounding Processes
5/22
Aim of Mixing
Reduce composition non-uniformity
Increase the probability of finding volume element of the minor at any
point in the blend (acceptable probability distribution)
Decrease the size of the domain
Break agglomerated particles
The mixing of two or more fluids or solid particles in a fluid consist of two
process, dispersive (intensive) mixing and distributive mixing.
Mixing and Composites Chee 490 18.10
Mixing
In almost all cases, good
distribution AND good
dispersion are required.
Distributive mixing can be
achieved by providing
convoluted flow paths that split
and reorient the flow repeatedly
Dispersive mixing can be
achieved by passing the
mixture through small regions
of intense deformation.
-
7/31/2019 Compounding Processes
6/22
Polimer mixing
Dispersive (Intensive) Mixing
Process whereby the solid particles or the minor
fluid phase are broken into smaller sizes.
Distributive Mixing
Process wheres the broken up domains distributed
into space and homogenized the the mixture.
mixing
increases only the
degree of
of the dispersed phase
mixing
increases the degree of
and
decreases of the
dispersed phase by
-
7/31/2019 Compounding Processes
7/22
Mixing and Composites Chee 490 18.14
Dispersive MixingDispersive mixing involves generating high stresses (shear andelongational) in the material to break down dispersed particles.These particles may be insoluble fillers (composites) or a second
polymer melt (blend).
Dispersive mixers force the material to flow over barriers that
form narrow clearances between mixing elements (i.e. between
extruder wall and a screw element).
-
7/31/2019 Compounding Processes
8/22
Dispersive Mixing
Concern in this process:
Droplet breakup
Happen by Interfacial tension, which keeps droplets whole.
Solid agglomerates breakup
Happen by Internal force, which makes solid particles form an
aggregates.
Particulates are used as fillers, color additives, modifiers and reinforcing
agent in polymers.
Because of electrostatic force etc. between primary particles of the
particulates, they form an agglomerates.
To get homogeneous mixture, its necessary to get the agglomerates be
broken, to their primary particles if possible
Dispersive Mixing
Break these agglomerates by using stresses generated by the flowing
fluid component.
Consider that force used to break the agglomerates = result of the
flow of the surrounding f luid.
Assume that the particles will break away as soon as the force
exceed the internal force (electrostatic, etc.)
Then assuming that the particle do not disturb the fluid flow field, the
flow field is homogeneous everywhere , making the deformation is the
same everywhere.
-
7/31/2019 Compounding Processes
9/22
Forces in Mixing
How the force transmitted, to break down agglomerates of additive
particles? By fluid mechanical stress in the mixer
Less energy is needed
Under high viscosity conditi
To achieve good dispersion
WHY?
Routes for Mixing
Route 1: with well distributed
but poorly dispersed additive,
will entail lower viscosity than
route 2.
Previous equation suggest
that Route 1 will require
more energy than Route 2
-
7/31/2019 Compounding Processes
10/22
Why distributive mixing is difficult to achieve in melts?
For example low viscosity system exhibits turbulent mixing
The boundry between laminar flow and turbulent flow is described by
Reynolds equation
V= velocity of the fluid, = density, = viscosity, D = diameter of circular
channel
Renolds Number must exceed 2000 for turbulence flow
Based on Reynolds equation, three viscosity regimes are seen to be;
At low viscosity, turbulence results in efficient distribution
At high viscosity (as found in polymer melts), turbulence cannot occur &dispersion is poor
At very high viscosity (as in rubber), there is sufficient shear to break downagglomerates & efficient distribution and dispersion can occur.
-
7/31/2019 Compounding Processes
11/22
Consider a channel where,
D = 0.5 cm = 0.005 m
= 150 Pas
= 1000 kg m-3
Q = 250 cm3 s-1 (Q is the amount of materials put
through a process/volume throughput)
Find velocity from the volume throughput
Low value of Re indicates that turbulent flow
cannot occur in polymer melts.
Distributive Mixing
Not concerned with interfacial energy, Particle breakup or domain
size reduction.
Not concerned with level of stress.
Concerned with rapidity and uniformity.
Application:
Miscible system (no interfacial tension)
Immiscible systems during initial stages (large domains) or afterdomain breakup
-
7/31/2019 Compounding Processes
12/22
Distributive Mixing
Distributive mixing involves stretching, dividing and
reorientating the flow of the polymer melt compound in order toeliminate local variations in material distribution and produce a
more homogeneous mixture.
Distributive mixers must impose high strain on the materialtogether with splitting and reorienting the flow.
Achieved by introducing barriers with large clearances thatgenerate a long, convoluted flow path.
Mixing and Composites Chee 490 18.24
Distributive MixingDistributive mixing involves stretching, dividing and reorienting
the flow of the polymer melt compound in order to eliminate local
variations in material distribution and produce a more
homogeneous mixture.
Distributive mixers must impose high strain on the materialtogether with splitting and reorienting the flow.
Achieved by introducing barriers with large clearances that
generate a long, convoluted flow path.
-
7/31/2019 Compounding Processes
13/22
Mixing and Composites Chee 490 18.25
Mixing Devices
Mixers can be classified into two categories:
Batch mixers: They are the oldest type of mixing equipment and are
still widely used. They are versatile units, because operating
conditions and the time at which the additives are incorporated can
be varied during a cycle to achieve optimum mixing.
Continuous mixers: They include single and twin-screw extruders,
and modified variants. Continuous mixing offers higher throughputs,
reduced manpower requirements and greater product uniformity,
leading to easier quality control. Disadvantages include less
processing flexibility, requirement for expensive feeding equipmentand generally lower dispersive mixing quality
Mixing and Composites Chee 490 18.26
A two-roll mill consists of a parallel pair of counter-rotating, heated metalrolls that turn at a slightly different rate (roll ratio), and provide an
adjustable gap (or nip) between them.
The shear stresses generated in
the gap are substantial, and provide
further compound mixing while shaping
the compound into a sheet.
Temperature control is more easily affected in a mill, when compared to a
Banbury-type mixer that completely encloses the compound.
Batch Mixing Devices
-
7/31/2019 Compounding Processes
14/22
Mixing and Composites Chee 490 18.27
Batch Mixing Devices
Internal mixers are high intensity mixers that work especially well in the
dispersion of solid particle agglomerates.
The dispersion of agglomerates
depends strongly on mixing time,
rotor speed, temperature and rotor
blade geometry.
The tangential rotor
design, or Banbury is
shown here, but several
variations exist, includingthe interlocking rotor
design known as
the Intermix type.
Mixing and Composites Chee 490 18.28
Continuous Mixing DevicesSingle Screw Extruders:
The SSE is a relatively poor mixing
device, and specialized screw
sections are needed to improve the
mixing efficiency of this apparatus.
Distributive mixing can be improved using static mixers or mixing heads
such as the pineapple configuration shown here.
Pineapple Mixing SectionKenics Static Mixer
-
7/31/2019 Compounding Processes
15/22
Mixing and Composites Chee 490 18.29
Continuous Mixing Devices
Dispersive mixing is more difficult, as it requires that high shear
stresses be generated. There are numerous designs for mixingsections, which can improve dispersive mixing (Maddock or Union
Carbide mixing section, Egan section).
These devices force the melt to flow over barriers, which form narrow
clearances between the screw and the barrel, thus improving
dispersive mixing.
Extrusion :Reciprocating
Control suhu mixingyang akurat
Shear stress secararelatif lebih rendah dariTwin Screw
Head pressure lebihrendah dibanding TwinScrew
Untuk CompoundFoam.
-
7/31/2019 Compounding Processes
16/22
Mixing and Composites Chee 490 18.31
Continuous Mixing Devices
Twin Screw Extruders:
TSEs have two screws within the barrel, and can be co-rotating orcounter-rotating, intermeshing or non-intermeshing. They are favoured for
Mixing and compounding
Chemical reactions / reactive extrusion
Devolatilization
Twin Screw Extruder
-
7/31/2019 Compounding Processes
17/22
Komponen screw
Extrusion: Continous Mixer
High Ouput
High Shear
Untuk mendispersikan
filer dengan ukuran
partikel mikroskopis
dan low aspek rasio
seperti carbon black,
pigment TiO2
-
7/31/2019 Compounding Processes
18/22
Mixing and Composites Chee 490 18.35
Continuous Mixing Devices
Mixing and Composites Chee 490 18.36
Continuous Mixing DevicesTwin-screw extruders use modular screws that are assembled from
screw segments fitted onto a common shaft. Conveying segments can
provide pumping, mixing and devolatilization, while non-conveying
elements such as discs and rotors are designed for kneading and mixing.
Thus, screws are easily optimized for a wide range of applications,
making twin-screw extruders extremely versatile.
-
7/31/2019 Compounding Processes
19/22
Dough Moulding Compound
The powders are charged first andblended for about a minute.
The resin (containing catalyst) andshrinkage control additive areadded and mixing is continued forbetween 15 and 30 minutes.
During this time the mixer isstopped occasionally and thewalls of the bowl scraped clean.
Once the slurry is homogeneousthe reinforcing fibres are added
gradually. These are blended intothe slurry until they are justdistributed throughout the mix - atime of about 5 minutes, typically.
Compone
nt
PHR Note
Res in 100 High reactivity resin having a maleic : phthalic
ratio around 2 : 1 and an alkyd : styrene ratio ofabout 70 : 30 by weight. The resin viscosity is inthe order of 10Pas.
Shrinkage
ControlAdditive
40-65 Also called a low profile additive. The material is
a solution of a thermoplastic polymer such aspolystyrene, polymethyl methacrylate, polyvinyl
acetate or polycaprolactone in styrene. Thesolution contains about 30% polymer by weight.
Used at ratios of 40:60 or 30:70 by weight on thehost resin.
Fillers 150-25
0
General purpose fillers include calcites and
dolomites. Eff ects fillers include aluminatrihydrate. The mean particle size of all fillersused in DMC is in the range 5mm-20mm with anoil absorption between 20-30. Exceptionally
larger fillers or fillers having higher oil absorptions
(up to 45) are used but at relatively lower levels.
Lubricant 3-5 Zinc Stearate, Calc ium Stearate
Catalyst 1-2 A relatively stable peroxide having a half-li fe of a
few minutes in the temperature range 100oC -130oC is used. Commonest materials are t-butylperbenzoate, peroctoate or dicumyl peroxide.Combinations of peroxides are used to fine-tune
the rate of crosslinking.
Pigment 5-10
Mixing and Composites Chee 490 18.38
Polyethylene-Nanosilica Composites
Transmission electron microscopy (TEM) images of
13 wt% SiO2/PE-g-PA 5 wt% SiO2/HDPE
(scale bars correspond to 200 nanometres).
-
7/31/2019 Compounding Processes
20/22
Mixing and Composites Chee 490 18.39
Polyethylene-Nanoclay Composites
Transmission electron microscopy (TEM) images of
40 wt% NR4+-MM/PE-g-PA 5 wt% NR4+-MM/HDPE
(scale bars correspond to 200 nanometres).
Mixing and Composites Chee 490 18.40
Polyolefin Blends - Nanocomposites
Idea to locate fillers preferentially in
one phase, to selectively reinforce it.
This can be accomplished by adding
functional groups having better
affinity with the filler, so that it will
migrate and exfoliate to thepreferred phase.
-
7/31/2019 Compounding Processes
21/22
Involve high shear process & much more powerful machinery
The simplest technique is two-roll mill
Some Processes and Machine (Compounding)
Two-roll millPair of rollers with a vertical nips between them
The polymer and additives are subjected to high shear in
the nip as the rolls rotate in opposite directions
Two-roll mill mixing started with rubber processing, now
exist for various function
Mixing on two-roll mill is time consuming, 2 h for a 200 kg
mix on a 84 wide mill, and depends on the skill of mill
operator
Schematic illustration of two-roll mill
http://rds.yahoo.com/_ylt=A9G_Rttg4q1EvXYAjY6JzbkF;_ylu=X3oDMTBkbGk3aHYwBHBvcwM2OQRzZWMDc3I-/SIG=1fhnr27nj/EXP=1152332768/**http%3a//images.search.yahoo.com/search/images/view%3fback=http%253A%252F%252Fimages.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimages%2526imgsz%253Dall%2526vf%253Dall%2526va%253Dtwo%252Broll%252Bmill%2526ei%253DUTF-8%2526fr%253DFP-tab-web-t400%2526b%253D61%26w=260%26h=160%26imgurl=www.lamseng.com.my%252F503.jpg%26rurl=http%253A%252F%252Fwww.lamseng.com.my%252Fquality.htm%26size=21.7kB%26name=503.jpg%26p=two%2broll%2bmill%26type=jpeg%26no=69%26tt=127%26ei=UTF-8http://rds.yahoo.com/_ylt=A9G_Rqo9za1E8jcAIG.JzbkF;_ylu=X3oDMTBkYTNwY3VnBHBvcwMxNgRzZWMDc3I-/SIG=1h70n18fe/EXP=1152327357/**http%3a//images.search.yahoo.com/search/images/view%3fback=http%253A%252F%252Fimages.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimages%2526imgsz%253Dall%2526imgc%253D%2526vf%253Dall%2526va%253Dtwo%252Broll%252Bmill%2526fr%253DFP-tab-web-t400%2526ei%253DUTF-8%26w=640%26h=480%26imgurl=www.kangshin.co.kr%252Fus_sub%252Fimage%252Fopen%252520roll.jpg%26rurl=http%253A%252F%252Fwww.kangshin.co.kr%252Fus_sub%252Fopenroll.htm%26size=40.9kB%26name=open%2broll.jpg%26p=two%2broll%2bmill%26type=jpeg%26no=16%26tt=127%26ei=UTF-8http://rds.yahoo.com/_ylt=A9G_Rqo9za1E8jcAFG.JzbkF;_ylu=X3oDMTBjb3ZrYjNkBHBvcwM0BHNlYwNzcg--/SIG=1h805lpst/EXP=1152327357/**http%3a//images.search.yahoo.com/search/images/view%3fback=http%253A%252F%252Fimages.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimages%2526imgsz%253Dall%2526imgc%253D%2526vf%253Dall%2526va%253Dtwo%252Broll%252Bmill%2526fr%253DFP-tab-web-t400%2526ei%253DUTF-8%26w=300%26h=225%26imgurl=www.kmutt.ac.th%252Fp-prof%252Ftwo-roll%252520mill_new.jpg%26rurl=http%253A%252F%252Fwww.kmutt.ac.th%252Fp-prof%252Fequipment.html%26size=35.9kB%26name=two-roll%2bmill_new.jpg%26p=two%2broll%2bmill%26type=jpeg%26no=4%26tt=127%26ei=UTF-8 -
7/31/2019 Compounding Processes
22/22
Banbury Mixer
2 rotors-counter-rotating within a chamber
Each has two or four blades which mix by smearing the
materials against the chamber wall
A weighted ram keeps the mix in place inside the chamber
Banbury Mixer vs. Two-roll Mill
The rate of output (200 kg batch of rubber
compound would take 2 h- two-roll mill. A
number 11 Banbury mixer produce 350 kg in
15 min or less)
http://rds.yahoo.com/_ylt=A9G_Rtve5a1EfXgAc6OJzbkF;_ylu=X3oDMTBjb3ZrYjNkBHBvcwM0BHNlYwNzcg--/SIG=1gormel62/EXP=1152333662/**http%3a//images.search.yahoo.com/search/images/view%3fback=http%253A%252F%252Fimages.search.yahoo.com%252Fsearch%252Fimages%253F_adv_prop%253Dimages%2526imgsz%253Dall%2526imgc%253D%2526vf%253Dall%2526va%253Dbanbury%252Bmixer%2526fr%253DFP-tab-web-t400%2526ei%253DUTF-8%26w=640%26h=427%26imgurl=www.soberayandsons.com%252FLabEquipment%252FBanbaryBMixer.jpg%26rurl=http%253A%252F%252Fwww.soberayandsons.com%252Fmixers.html%26size=81.7kB%26name=BanbaryBMixer.jpg%26p=banbury%2bmixer%26type=jpeg%26no=4%26tt=267%26ei=UTF-8