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melt viscoelasticity of polyethylene terephthalate resins for low density extrusion foaming.

by:Top-In     2020-08-09
M. XANTHOS [*,1]U. YILMAZER [**]S. K. DEY [*]
Flow properties of conventional polyethylene ester (PET)
Resin is not particularly suitable for low density extrusion foaming with physical foaming agent;
As a result, chemical modified resins that are usually used through chain expansion/branching reactions.
This resin has a higher overall melt viscosity and a higher melt strength/melt \"elasticity\" than the unmodified material \".
In this work, after reviewing the existing technologies of chemical modification of PET, an unmodified and chemically modified resin was selected, and its molten viscous properties were characterized, including shear and dynamic complex viscosity, storage in the wide shear rate/frequency range
Some flow models help to provide better whole Viscosity curve fitting for unmodified
Modified resin.
Foam extrusion with variable density (from about 1. 2 to 0. 2 g/cc)
, Prepared by carbon dioxide injection in a single-layer flat extrusion device.
Foam with lower density, less than 0.
5g/cc, obtained only by increasing the gas pressure in the case of chemical modified resin.
The effects of variables such as physical spray concentration, resin flow, resin thermal properties and process condition selection are related to product properties (including density, battery size and crystalline degree.
This paper introduces the extrusion foaming of medium and low density thermoplastic foam for the production of polystyrene (PS)
Low density polyethylene (LDPE)
It has been successfully carried out for a period of time by injecting a physical blow agent ,(PBA)
Single or series lines.
The PBA is an \"environmental friendly\" atmospheric gas, volatile hydrocarbons, or HCFC (HCFC)
, Measured and dissolved in polymer melt during processing.
It is believed that the shape of the bubble is uneven from [1]. As the gas-
Take out the filled melt from the mold and it experiences a sudden drop in pressure;
This thermodynamic instability leads to phase separation.
The escaping gas results in expansion in the fluid matrix, causing a single bubble to merge into the cell and to produce a stable expansion structure through subsequent solidification [2, 3].
Extrusion foaming to the desired microstructure and properties is a complex process controlled by the interaction of material properties (
Polymer, nuclear agent, foaming agent)
Process parameters (extruder. screw, die)[1, 4].
Conventional gas injection extrusion foaming usually results in a microstructure with a lower density and has a polygon battery that typically ranges from 50 to 250 [E. G. mu]m in size.
The foam of about 10 [finer] closed cellsmu]
Minimum size and cell density [10. sup. 8]cells/[cm. sup. 3]
Known as Microcell [5]
And has a certain improvement performance than the traditional foam.
In the original Microcell batch technology that Kumar and Weller [watch]6]and Park et al. [7]
, Hot plastic polymer is pressurized, non-
Reaction gas like [CO. sub. 2]
Usually at room temperature.
The polymer is then heated to the foaming temperature close to the deposition temperature [of its plasticized glass]T. sub. g]
Promote phase separation and guide the growth of dual cores and bubbles.
The size of the battery and the density of the battery depend on the saturated pressure and the amount of dissolved gas [8].
Research is under way to develop continuous extrusion Microcell process through gas injection, single line or series production line equipment with static mixing and special molds d [7, 9]
It may cost-
Effective competition with traditional extrusion foaming.
The viscous properties of molten polymers and their freezing capacity are critical at all stages of flow
Whether it\'s a macro or a micro foam, the density squeezes out the foam.
As discussed by [throne]1]
, A melt with a relatively low shear and tensile viscosity is required during the initial foaming stage to allow the bubble to grow rapidly.
However, at subsequent stages, the viscosity must increase, for example by cooling or strain hardening, to a level sufficient to stabilize the growing bubbles.
In addition, the requirements of the polymer are: moderate High Tensile viscosity to allow two-way stretching, high melting strength/\"elasticity\" to prevent membrane tearing (blow-out)
And promote the formation of closure
Cell structure, if crystalline, The Crystal speed is relatively fast.
Compared with commonly used PS and dlp, traditional polypropylene (PP)
High Density Polyethylene (HDPE)
PET resin is not conducive to low density foaming due to its insufficient physical properties at the processing temperature.
Low melt viscosity, low melt strength/\"elasticity\" of conventional relatively low molecular weight \"(MW)
And narrow molecular weight distribution (MWD)
Bubbles that resin does not help to control cell expansion and steady growth [1, 10-12].
For this resin, Flow modification is carried out by the change of MW and MWD [13]
Can be done either through additives or during reactor/post-processing
Reactor treatment for chain expansion, grafting, branching, control of cross reaction
Link or control degradation.
Interest in foamable semiconductor adhesives is caused by the combination of their good mechanical properties and dimensional stability at high temperatures (up to200[degrees]C for PET).
In particular, the foaming of PET poses some challenges to the required high processing temperature [260-290[degrees]C]
Compared with amorphous resin, there is no wide extrusion foaming window, the Crystal speed is slow, the process stability is limited, and there may be interference between the crystal core and the bubble core.
In addition, the known sensitivity of PET to hydrolysis, thermal or thermal oxidation degradation exacerbated poor foaming properties.
This article is part of a broader research effort to determine after
Consume recyclable PET as foamedcore in laminating materials for construction and building applications.
Following a review of the chemical modification methods of PET Resin, one of the objectives of this work is to linear with achain-
From the perspective of melt viscosity elasticity, the extended/branching PET resin is related to its extrusion foaming properties under controlled process conditions.
A single extrusion line with flat die was used [CO. sub. 2]
As a blow agent.
The flow data discussed below include capillary shear and dynamic complex data as melt viscosity indicators, as well as mold expansion/storage modulus data as melt elasticity indicators.
\"Chemical modification of PET-
For applications such as foaming, extrusion blow molding, or simply upgrading low-characteristic viscosity materials, modified PET resin with improved flow and melting strength can be produced by a chain expansion/branching reaction with di-
Or multi-functional reagents.
The reaction mainly occurs between the carboxyl/oh polyester terminal and the compounds containing functions, such as Malay ester or shrink glycerin, and also includes oxazol salt, isocyanate acid, carbon Dione, oh,14].
In the context of PBA injection of low density foaming, a variety of modification methods have been reported, mainly in the patent literature.
It should be noted that important flow parameters are usually expressed as single point, single temperature and single shear rate values that are more suitable for quality control purposes;
However, in a few cases, complete flow data for foamable.
Non-foam resin is reported.
Here are examples of chemical modification methods: reactor polymerization in the presence of modifiers.
For example, Muschiatti [15]
High support, high melting strength, non-
Newton behavior resin is suitable for the preparation of low density closed foam by polymerization in the presence of a support agent (
Hydrogen, alcohol).
Recently, Imaizumi and others. [16]
Extruded foam.
The support of polychlorhexene resin was prepared by polymerization of less than 0.
Mole % of three functional monomer.
The modified resin has a wide MWD, which improves the melting tension by introducing long chain branching, and exhibits strain hardening during Tensile viscosity measurement.
Solid statement in the presence of a pre-mixed modifier by solid-state polymerization with a pre-mixed modifier to produce a pba extrusion foamable polyester modifier, E. G. g.
Average heat agent two Malay (PMDA)
Discussed in a series of patents and publications in Sinco Engineering [10, 17-22].
These resins are different from non-resins.
By increasing the viscosity of the characteristic, IV ,([greater than]0. 9 dl/g)
, Increase the melt strength, high mold expansion, increase the non-complex viscosity
Newton behavior in low frequency region and higher storage area (G\').
Supported foamable PET is also prepared by mixing with Ethylene polymers containing acrylic acid, Ester, alcohol function, followed by a solid statement to produce 10-
Fold higher melt viscosity, higher mold expansion and melting strength compared to unmodified resin [1]23]. Post-
Modification of reaction extrusion reactor.
Extrusion of PET in the form of concentration with PMDA or other supporting additives can lead to a significant increase in zero shear viscosity, an increase in melting strength and extrusion expansion, an increase in molecular weight, and an increase in multi-dispersion ratio [M. sub. z]/[M. sub. n]
Than from about 4. 5 to up to 11.
The change in performance depends on the selection of process conditions, the concentration of additives and the type of carrier [14, 24, 25].
The modified ingredients can reach 0.
2g/cc density of [series lines with HCFC25].
In another patent, Hayashei et al. [26]
Through the modification of PMDA, a 3-
For foaming, it is necessary to increase the expansion of the folding mold and increase the melting strength.
By significantly increasing the shear viscosity and melting strength of PET, electro-hydrogen compounds and metal catalysts are used to produce hydrocarbon/inert gas extrusion foamable PET [27].
In the presence of different carriers and various additives, PMDA concentration is also used to improve the stability of the foaming process [28, 29].
Reaction Mechanism of Asuggested [4, 24]
With the PMDA extending as the first steplinear, the reaction of the end polyester end-base with the function of Malay ester (Fig. 1)
And the PMDA part of each binding forms two amino groups.
The subsequent reaction may involve all the functions of the PMDA molecule, resulting in branching or even cross-reactions by means of the ester and transformation reactions
Link structure.
The combination of PMDA/tripentyl alcohol/Lewis acid catalyst has also been used to produce resin with modified Rheo [j]30].
Other modifiers such as multi-functional epoxy chain expansion compounds are also used in series [CO. sub. 2]
Produce foam with 40 kg /[m. sup. 3]density [31];
Adding four functional epoxy reactive additives to the intermittent mixer to produce PET with increased Tensile viscosity and foaming melting strength [32].
[Proposed mechanism33,34]for chain-
The extended reaction with the active ions of the shrink glycerin includes the ester of the end amino group and/or the ether of the end group (Figs. 2 and 3);
Secondary phenol formed by these reactions may further react with amino or epoxy groups that cause branching or cross-linking.
A summary of possible reactions to convert linear polyester into partial branching resin can be found in the reference. 4.
The following resin was used for the experimental resin: *
Chemical modified PET (reactor (PET4)
: Based on the experimental grade of recycled bottle material and modified by solid-state Poly [Extension/branch with PMDA]17, 18]
Foam extrusion of plates and plates (
New Engineering).
Report nominal IVof 0.
95 after modification
As reported in our previous publication [11]
Measuring MFI at 260 [degrees]C/2. 16 kg is 4.
38 and 270 [tested extrusion Wells]s. sup. -1]/260[degrees]C is 2. 86.
* Modified pets (PET8)
: The typical thermoforming APET grade is probably linear ,[Traytuf. sup. TM]9506, Shell)
The nominal IV is 0. 95.
As reported in our previous publication [11]
, Measured MFI at260 [degrees]C/2. 16 kg is 10.
4 and measuring extrusion expansion at 270 [s. sup. -1]/260[degrees]C is 1. 39.
Capillary melt viscosity of pre-drying materials and expansion shear viscosity of extrusion materials ,(
Usually on night 10. 130[degrees]C)
, Was determined using a Kayeness capillary rheometer with a mold radius of 0.
Length/diameter is 523mm and 15:1.
Viscosity Measurement at 270-290[degrees]
C. within the shear rate range of 134 to 20,000 [s. sup. -1].
Considering that at a given volume flow rate, the pseudo-plasticity is greater than the hearing rate of the Newton fluid at the wall [35]
, The corrected viscosity value is calculated by using the Rabinowitsch correction factor.
Details of the correction procedure can be found elsewhere in [36].
Flow instability of modified PET4 resin significantly at higher shear rate and lower temperature is not allowed to collect viscosity data higher than 268 [compared to unmodified PET8 resins. sup. -1]at270[degrees]C and 7000 [s. sup. -1]at 280[degrees]C.
Therefore, in the wide shear rate range, full protection of the two materials may be only 290 [degrees]C.
Extrusion expansion measurement is a function of temperature and shear rate and is also determined by using a CCD camera/Recorder/TV device at a distance of 9mm from the dead outlet in the Kayeness capillary viscosity meter
The extrusion expansion is recorded and then analyzed using the screen scale provided in the microscope.
Details of the experimental techniques can be found elsewhere in [36].
To average the deviation and provide repeatable results, repeat four times per run.
Dynamic mechanical properties of complex viscosity[eta]. sup. *]
, Measurement of RMS of mechanical spectrometer using flow rate-collection of energy storage modulus G\' and loss modulus G \"data for pre-drying materials as a function of frequency
The disk mode under nitrogen is 800.
The system is programmed to perform frequency scanning in the range of 0.
1 to 280 rad/s at temperatures of 100 and 290 [degrees]C.
Extrusion foaming]CO. sub. 2]A 32 mm dia.
, Using a 40 L/D thousand ton segmented single screw extruder with a gas injection port and a screw configured for gas dispersion and dissolution.
A combination of a 250mm-wide flat die and a three-fold chilledroll assembly (Fig. 4), was used.
Pre-drying resin ,(20 hrs at120[degrees]C)
, In the absence of an additional crystal core agent, it is measured into the hopper and plastic is added within the length of 19D. [CO. sub. 2]
At this point, it is injected at different pressures and mixed into the melt.
In order to get high gas pressure, the Air drive booster was used.
As the gas pressure increases, the melting pressure of the modified material ranges from 6500 to 11,600 kPa;
Melting temperature of the mold from 265-267[degrees]C.
For unmodified foam resin, at about 6900-
7500 PA, while the melting temperature is 258-260[degrees]C.
The density, cell size and uniformity of all extrusion materials produced under different gas pressures were analyzed by liquid displacement and optical microscopy.
The amount of heat scanned by differential scanning (
20 \"first heating]degrees]C/min, Perkin-Elmer DSC-7)
For the glass transition temperature ,([T. sub. g])
, And the peak temperature and enthalpy associated with cold crystals ,([T. sub. cc]and [Delta][H. sub. cc]), and fusion,([T. sub. f], [Delta][H. sub. f]).
Calculated percentage of crystals ([Delta][H. sub. f]-[Delta][H. sub. cc])/[Delta][H. sub. pf]], where[Delta][H. sub. pf]
Fusion heat of perfect pet Crystal takenas 125 J/g [J]37].
Foam plates for thermal analysis are allowed to deadsorption at least 10 days prior to testing to prevent possible gas generation during heating. The 5-
The 10 mg DSC sample cut from a rough foam is actually a solid sample and does not contain any microscopic cells that may burst or affect heat conduction during the measurement process.
The main purpose of the DSC experiment is to distinguish the two resins and determine [CO. sub. 2]
As reported in the literature, induced crystals occur during cooling.
Calculation of the results and discussion of the Viscosity curve of PET Resin by calling Cox-
Merz rule, which states that the size of the complex viscosity and shear viscosity data can be compared in the case of equal frequency and shear rate [38], Figs.
5 and 6 show the combined experimental data points for unmodified and modified PET resin.
The curve fitting to be discussed below is also shown.
[Get of data]degrees]
C includes a complex viscosity value of 0. 1-
100 rad/secrange ,(
No, no.
Uniform stress field)
, And capillary shear viscosity values ,(
In the application of Rabinowitschcorrection)
, Obtained at a shear rate of more than 134s. sup. -1].
Material degradation may be one of the factors that lead to the occurrence of non-continuity in the transition area.
Material degradation can occur at a higher frequency ([greater than]50 rad/sec)
This occurs at the end of the sweep meter experiment, and also at a lower shear rate, due to the long-term stay in the flow tube.
PET4 resin based on recycled raw materials is more likely to degrade.
FIG data.
5 and 6 indicate important differences between the two resins: PET8 displays typical Newton behavior in low frequency regions, from 50-100[s. sup. -1].
In contrast, PET4 appears to behave as a power-law fluid starting shear in almost the entire shear rate region
Thinning at low shear rates: this behavior would be typical of branching or wide mwd polymers ,[39]
Including mixed recycled materials40]
, And higher MW resin [39].
Although the IV is lower than the sample used in the current work, it is 265-295[degrees]
C of the highly supported PET sample was reported;
This sample also has a slightly higher activation energy for the flow of the melt compared to the linear sample [41].
As mentioned earlier, only the PET8 resin used in the current work can obtain a complete flow curve at three temperatures.
This allows the calculation of the activation energy values of the viscous flow, which decreases with the shear rate from about 65 kilojoules/moles to about 20 kilojoules/moles in the capillary flow shear rate region.
However, since the data of the two resins cannot be collected at all temperatures and shear rates, the pet8 activation energy value and chain-
It is not possible to extend/branch pet4.
The viscosity of PET4 is generally higher than that of PET8 at [FREQUENCY]less than]
20 rad/sec and shear rate [greater than]134[s. sup. -1](Fig. 7).
This is consistent with the measured melt flow index values, but not with the reported IV values, which are determined independent solutions that do not include the effects of entanglement. Across-
Seems to have happened in the 20-20 range. 100 rad/sec.
In fact, however, this cross
There is no extension of over in the capillary viscosity zone, which indicates:)
Accuracy of high frequency data (
Nitrogen blanket though)
There may be problems with the accuracy of and/or low shear rate data, B)the Cox-
Merz rules are poorly applied in areas with high frequency, c)
It is necessary to correct it because there is no
Uniform stress field in parallel disk measurement.
It is worth noting that the viscosity curve of pet4 resin reminds the resin used in Extrusion blow molding, which is also modified through the branch of the multi-functional additive, similar to the resin with foaming grade [1]42-47].
In addition to the high melting strength, the grade with high shear sensitivity in blow molding (
The low melting viscosity of the mold, the high viscosity of the blank when blowing)arerequired [48].
For example, a suitable extrusion blow molding PET modified by branch in a reactor has a zero shear viscosity/viscosity ratio @ 1000 [s. sup. -1]
About 35, and only 10 of the inappropriate unmodified resin (42, 43).
Zero shear viscosity/viscosity @ 1200 [by comparison [s. sup. -1]
The ratios of PET4 and PET8 were approximately 20 and 6, respectively, indicating similar trends in shear sensitivity.
Modeling six different parameter models: Bueche-
Elin Harding (two parameter)
, Carreau, Cross, suterby (threeparameter)
Model and vinogrdorf (four parameter)[49].
All models include the limit viscosity at a high shear rate ([dot{[gamma]}])
Set to zero and ask to calculate the value of power lawindex (n)
Zero shear viscosity ([[eta]. sub. 0])
And characteristic time constant ([tau])
, In the case of the Vinogradov model, anon-
Dimensional constant.
Details of the computer program used can be found in [other places]36].
Non-computational mean power law index values from fully developed
Newton capillary data is 0.
29 pairs of PET8 and 0. 49for PET4.
All models used are applied to the complete ,(
Capillary and complex)
, Viscosity curves, including points at discontinuous points and possible points for degradation.
Almost all models fit the Newton region of PET8 well, but have encountered problems with non-continuity;
Cross model ,[eta]/[[eta]. sub. 0]= [[1 +[([tau][dot{[gamma]}]). sup. 1-n]]. sup. -1], shown in Fig.
5, and the thesby model (not shown)
It is found that the whole flow curve is modeled reasonably.
The data from PET4 proved more difficult due to the lack of a clear Newton region, which most models assume.
Again, the Cross model (Fig. 6)
The Sutherby model provides better adaptation for pet4.
Our results are basically consistent with the results obtained by elbirli and Shaw when simulating low density polyethylene and high density polyethylene using similar models and methods [50].
These authors found that the best two parameter models are Eyring, and Cross is the best three parameter model, which has not improved the fitting accuracy.
Melt Strength/\"elasticity\" standard term \"melt elasticity\" although not appropriate
It is widely used in polymer processing. in polymer processing, complex geometric effects and flow fields need to use linear viscous elastic functions or their non-
Linear correspondence.
Elastic recovery (recoil)
It has long been considered a useful parameter for determining fluid elasticity.
It is a form of storing energy that can be used with things like \"stability-
State shear compliance \"or\" recoverable shear strain \".
The change of \"melt elasticity\" is related to the change of the value of the viscous elasticity function, such as the normal stress difference, the energy storage modulus and the actual importance parameters (such as the mold)extrudate)swell [51-53]
The latter indicates the recovery of storing elastic energy.
For some polymers, the change of \"meltelasticity\" is also related to the change of Tensile viscosity [54]
, And melting strength, latterbe related to tensile flow [qualitative]52, 55].
For example, so-
Foaming PP called \"high melting strength [56]
With higher melting tension values and tensile flow behaviors, these behaviors are significantly different in nature from conventional PP resin with the same melting flow index, and have higher differences in value.
Under high tensile strain, the Tensile viscosity tends to increase (
Strain hardening\"
, Similar to low density polyethylene that is easy to foaming (LDPE)
Resin with long chain support [57].
The \"high melting strength\" PP also has high dispersion ,([M. sub. z]/[M. sub. w])
, From the point of view of the specific limit value of balance compliance and recoverable strain [, the high \"meltelasticity\"58].
Under normal circumstances, the literature shows that a similar modification on the molecular structure can obtain a higher melting strength and a higher \"melting degree\" at the same time \".
Regarding the resin used in this work, at all experimental temperatures and shear rates, the mold expansion of PET4 is much larger than that of pet8.
The maximum expansion ratio experienced by PET8 is 1.
The expansion ratio of PET4 is more than 3.
3. depending on the test conditions.
It should be noted that the PET8 did not have a molten fracture during the measurement, except for several readings at the highest shear rate [270]degrees]C.
In contrast, pet 4 often experiences molten fracture even at the highest test temperature.
Figure 8 compares the two resins at 290 [degrees]C;
Expansion ratio increases with the increase of shear rate59].
According to the shear rate, the mold expansion of PET4 is on average more than twice that of PET8.
It should be noted that for the PET4 data, the unstable area (
Ripple and spiral)
Significantly higher than 1000 [s. sup. -1].
Although it is well known that structural parameters such as MW, MWD and long chain branching have a profound impact on expansion properties, shear Tensile viscosity and melting strength [1]60]
, Increase the difference between the relative importance of MW
Expanding MWD is not an easy thing [61, 62].
The limited experiments carried out in this work do not allow further speculation about the exact differences in molecular structure of the two PET resins used.
Another measure of \"melt elasticity\" is storagemodulus G\' or in-
Phase component of the complex modulus.
Compare the value of G\' as shown in the figure
9. a similar conclusion is caused by the expansion of extrusion.
At low frequencies, the value of g\'ofpet4 is 10 times larger than the value of PET8 and begins to converge as the frequency increases.
At low shear rates, there will be more entanglement due to the presence of branching or high mw molecules;
Therefore, chain interaction plays a more important role, thus increasing the storage modulus of pet4.
As the frequency increases, the importance of entanglement decreases.
As expected, the oss modulus G \"of PET4 shows the same trend as the complex viscosity in figure 17, i. e.
It is 20 rad/sec higher than PET8 and may have crossIt ends thereafter.
The extrusion foam density and bubble size of the foam layer are about 1.
Figure 1 summarizes the 2mm thickness produced by the flat die at different gas pressures.
10a and l0b and Table 1.
For chemical modified, high viscosity, high melting strength PET4 resin, the density of foamedextrudates decreases rapidly with increasing gas pressure, up to 5000 kPa;
Since then, its level has dropped to about 0. 2-0.
3g/cc in the gas pressure range of 5500-11,000 kPa.
The cell size also seems to be stable around 0. 3 mm;
As expected, the cell size distribution is very extensive, as can be seen from resins that do not contain additional nuclear factors.
For unmodified, lower viscosity, and lower melting strength PET8 resin, the density of foam extrusion also decreases with the increase of gas injection pressure.
However, the minimum damage density is significantly higher than the PET4--(0. 7-0. 8vs. 0. 2-0. 3 g/cc)--
And get it at a lower gas pressure range from 3000 to 5000 kPa.
With this special resin, it is impossible to produce a satisfactory foam with a lower density by increasing the gas pressure of more than 5500 kPa.
And collapse of cells.
The overall bubble size of the higher density PET8 foam seems to be smaller than the pet4 foam, but the size distribution is still quite extensive.
The bubble expansion in the foaming process has obvious similarities with the blank expansion in the extrusion blow molding process.
In both cases, a strong elastic melt that can be stretched evenly without thinning or tearing is required.
The results of this work are basically consistent with those of cheung et al. [63]
Park and Zhang [64]
Who observed cell density in the plateau[CO. sub. 2]
Compare the concentration curves when high melting strength supports PP and traditional resin, which are foamed in small molds under high mold pressure.
Reaching the gas solubility limit is one of the reasons for the observed plateau.
The same author attributed the difference in cell density between supporting and non-supporting pp materials to the difference in nuclear activation energy caused by the difference in polymer surface tension caused by branching.
This difference in surface tension is likely to exist between PET4 and pet8 resin for this work, although from the limited experiments currently available, these effects cannot be quantified.
It is generally believed that only soluble gas should be injected into the polymer melting stream, and excessive gas is harmful to cell structure [1, 4, 7, 65].
For common foaming resins such as PS and PE, the solubility and diffusion coefficient of physical blow molding agents were studied in a wide temperature range until the melting process temperature [1] as a function of pressure66, 67].
However, these data for amorphous or semi-crystalline polyester (PET,PETG)
Usually only for lower temperature [68-70]
, Corresponding to the gas saturation and foam temperature used during the batch micro-foam process [71-75].
Preliminary data on the stability of gas in PET melt (270-290[degrees]C)
As a function of melting pressure using in-
Wire optics has only been reported recently. 76].
Under the treatment conditions used in this work, if there is no gas solubility data, the gas injection pressure can only be considered as a total concentration indicator that may exceed the capacity limit.
Injection in the partially filled area of the segment screw initially results in two-
The phase system further downstream can be converted in a single
A combination of a phase system or a single
Phase and non-dissolved gas clusters according to screw configuration, operating conditions, temperature, etc.
Such clusters can act as premature nuclear factors that affect the microstructure of the foam (
Number of cells, wide size distribution)
Surface texture [4].
In fact, the rough surface texture, cell rupture and ripples observed at high gas pressure, especially at PET4, indicate that some of our experiments have exceeded the gas solubility limit.
It should be noted that considering the large area that can be used for gas escape, the foaming efficiency in the relatively thin single layer produced with the current flat die is lower than the best [77].
ABA coextruded structure with A solid cap layer will reduce gas loss [78].
Another factor that affects the quality of this work to squeeze out foamedsheets is the use of a flat die that only allows twice
Size gas expansion]12].
The ring mould and the cooling core rod can hold three
The size expansion of the extrusion is carried out in a more controllable manner.
For all plates with a density of less than 0.
5g/cc in the plate mold for this work, the difficulty of gas expanding horizontally leads to the folding of the plate, which leads to the observed ripple parallel to the direction of the machine. [T. sub. cc], [T. sub. f]
The percentage of crystals may be [T. sub. g]
Foam to different densities ofsheets seems to depend only on the type of resin, not the gas pressure, as suggested by the range of values obtained for the different gas pressure ranges used for each resin (Table 2).
Lower value [T. sub. cc]
The higher the overall crystal level of PET4.
Pet 8 foam may be related to the presence of impurities and/or residues of non-reactive chemical modifiers.
This additive can accelerate the crystal ,(
Promote faster stability of cells)
, And lead to a higher percentage of crystals under the process conditions used. Lower peak[T. sub. f]
The value of PET4 resin can be attributed to the presence of side branches that introduce defects in crystal flakes;
In addition, the wide range of crystal structures variable the perfect molecular weight distribution of thepost-
Consumer raw materials for chemical transformation.
The crystalline degree of the solid PET4 and PET8 plates produced under cooling conditions, similar to those used for foaming, is determined to be 24. 1%and 6. 6% respectively.
Therefore, by comparing these solid values with the foam values of table 2, it seems that no [CO. sub. 2]
Induced crystals--
Has been reported by various authors before [71, 75]
PET foam plastic-
It happened in our system.
Conclusion The chain extension/branching PETresin and linear resin with chemical modification were evaluated for the melt-viscous energy associated with the sheet extrusion foam, both of which have relatively high nominal IV.
With regard to the melt viscosity, the chemical modified resin has:)
The overall melt viscosity is high ,(
Shear and composite)
, Modeling the entire frequency/shear rate range fairly well with a crossover or satherby model;
In addition, higher loss modulus G \"in the low frequency dynamic range \". b)early shear-
In the whole viscosity, there is no dilution of Newton region.
Shear rate/frequency curve, which is an indication of branch, higher MW and/or wide MW;
In addition, the high shear sensitivity is reminiscent of the behavior of the resin suitable for extrusion blow molding.
Regarding the melting strength/\"elasticity\" standard, thechain extension/branching resin has a higher extrusion expansion in the range of foreign capillary shear rates and a higher G\' in the low frequency dynamic range\'
Under low temperature and high shear stress, a certain flow instability associated with the high viscosity and elasticity of the resin was observed, at a wide shear rate, at storage, and at a loss modulus, extrusion expansion seems to be an adequate flow standard to distinguish the extrusion foaming behavior of the two resins in a flat die, without more tedious measurements of properties such as Tensile viscosity, melting tension, or MWD.
Higher viscosity and \"elasticity\" of chain length/branching resin allow the production of foam with lower and lower density ,(
The density is about 0. 2 g/cc)
By increasing the air pressure.
In addition, rapid crystals to high levels of crystals seem to help stabilize the development of cell structure.
However, due to the main two
The size of the extrusion expands and the ripples are observed in the low density film;
This may also be related to excessive injection of gas beyond its dissolution limit.
High gas pressure in a linear, lower melt elastic/strength resin causes the battery to blow-
Blistering is not allowed under about 0. 7 g/cc.
Experiments are under way to optimize the foaming process by determining the solubility and diffusion coefficient [CO. sub. 2]
Under the condition of PET melt extrusion process.
Similarly, experiments are being carried out to determine the thermoforming properties of the sheet produced and to evaluate the cores in the laminated sandwich structure.
The author would like to thank the doctor for his contribution. H. Al-
Ghatta of Sinco engineering provided experimental PET4 for this work.
Financial support from various parties
Center for Life Engineering Research (MERC)
New Jersey Institute of Technology (NJIT)
Through funding from the New Jersey Science and Technology Commission and the polymer processing Institute.
The author wishes to acknowledge the help of the doctor.
Victor Tan, Institute of Polymer Processing (PPI)
In qualitative work and Mr. Q.
Zhang of NJIT is in the extrusion experiment.
Department of Chemical Engineering, Chemistry and Environmental Science, Newark Institute of Technology, NJ 07102 (*. )
In addition: Newark GITC building kit 3901 Institute of Polymer Processing, New Jersey Institute of Technology, New Jersey 07102 (**. )
Department of Chemical Engineering, Middle East Technical University, Ankara, Turkey (1. )
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