MCR302 shear rheometer manufactured by Anton Paar GmbH was used for determination of shear viscosity, structural and viscoelastic properties of the reference resins. CC27 concentric cylinder (inner cylinder effective length 40,024 mm and diameter 26,665 mm;
outer cylinder positioning length 72,5 mm and diameter 28,920 mm) was mainly used but also ST-24 paddle spindle stirrer was tested. Viscosity curve, amplitude sweep to determine the linear viscoelastic region of the resins and frequency sweep were performed. For viscosity curve, shear rate was varied first from 1 to 100 1/s and then from 100 to 1 1/s.
Shear rate was also varied from 1 to 500 1/s and from 500 to 1 1/s. For amplitude sweep, strain varied from 0,01 to 100 % and frequencies of 15, 10 and 1 rad/s were used. For frequency sweep, angular frequency varied from 500 to 0,5 rad/s and strains of 1, 0,5 and 0,1 % were used. Measurements were performed in temperature of 25 ºC.
HAAKETM CaBERTM 1 capillary break-up extensional rheometer manufactured by Thermo Fischer Scientific Inc. was used for determination of elongational properties of the experiments. Plates of 6 mm were used, so also the sample diameter was 6,0 mm. Initial and final aspect ratios defining the sample elongation were 1,00 and 2,75, respectively, so the sample initial height and final heights were 2,99 mm and 8,24 mm, respectively. System imposed axial Hencky strain (εf) was 1,01, which is between the optimal range (1 < εf < 2) determined by Anna & McKinley (2001). Measurement duration was 2 s and sampling rate 4000 Hz. For each experiment, at least 6 replicates were done and for each replicate 2 elongations. The repeatability was good. The resin filament diameter was measured as a function of time and the break-up time determined. The diameter was normalized for scale 0-1. Apparent extensional viscosity curves were plotted as a function of strain. Plotting was performed by V4.50 CaBER Data Analysis software. An average curve for filament elongation was calculated for each sample based on at least 5 replicates. Average apparent extensional viscosity curves were calculated for part of the experiments, and in calculations, LPF resin density 1,2073 g/cm3 and surface tension determined by pendant drop method were used. Measurements were performed in temperature of 25 ± 2 ºC.
Effect of additive dosage increase was studied and working curve coefficients were computed via regression analysis (multiple linear regression, MLR), tool available in Microsoft Excel Data Analysis Add-Inns. Regression analysis models the relationship between multiple explanatory variables and a response variable by fitting a linear equation to observed data (Montgomery et al., 2012).
Interfacial viscoelastic properties of the experiments were determined by using CAM 200 optical contact angle and surface tension meter manufactured by KSV Instruments Ltd and PD-100 pulsating drop module. LPF resin density 1,2073 g/cm3 was used in heavy phase settings and air as light phase. Drop volumes used were 27 μl, 11 μl and 15 μl for PF resin, PF curtain resin and LPF resin, respectively, which were the maximum to be formed and not to drop during the measurement. Measurements were performed at frequencies of 0,05 Hz, 0,10 Hz and 0,25 Hz. Frame interval of 1 second and 50 frames were recorded at frequencies of 0,10 Hz and 0,25 Hz and frame interval of 2 seconds and 30 frames were recorded at frequency of 0,05 Hz. OscDrop software were used in calculation of results. At least 3 replicates were performed at each frequency for each sample. For every measurement, a new drop was formed. The repeatability was variable. Average values were calculated at each frequency for each sample. Measurements were performed in temperature of 23 ± 1 ºC and relative humidity of 50 ± 2 %.
10 RESULTS AND DISCUSSION
Next, the results of the analyses are performed and discussed. In addition to general properties of the resins, surface tension was determined by pendant drop shape analysis method and De Noüy ring method, surface free energy was determined via contact angle measurements, shear (viscosity curve, amplitude sweep and frequency sweep) and extensional rheological properties (filament break-up time and capillary velocity, apparent extensional viscosity) were determined and interfacial viscoelasticity by oscillating pendant drop shape analysis method was determined. Properties of LPF resin were modified with commercial additives.
Based on these measurements, Table XVII and Table XVIII can be presented. Table XVII summarizes the suitability of the measurement for determination of resin properties. Table XVIII summarizes the performance evaluation of the additives to modify resin properties.
Table XVII Review of analytical methods performed in this work.
Analytical method Suitability Comments Reference to this work
Surface tension +
Clear differences between the resins obtained. Pendant drop method simple, reliable and accurate.
Chapter 10.2, Appendix III
Surface free energy - Drying of resins not applicable, repeatability not good.
Clear differences between the resins obtained in filament break-up and capillary velocity. Extensional
Table XVIII Review of additives used in this work.
Additive
Studied dosage,
% of the weight of resin
Surface tension Elongational properties
Surfactant 1 0,2; 0,4; 0,6 Elongation: 0,2
Efficient ST reduction, higher dosage possible.
Dosage to reach PF curtain resin ST: 0,16 %
Slight improvement in filament break-up time obtained.
Capillary velocity remarkably affected.
Surfactant 2 0,1; 0,2; 0,4; 0,6 Elongation: 0,1
ST reduced, CMC achieved: 0,40 %.
Dosage to reach PF curtain resin ST: 0,13 %
Excellent improvement in filament break-up time obtained. Capillary velocity remarkably affected.
Surfactant 3 0,2; 0,4; 0,6 Elongation: 0,6
ST reduced, higher dosage possible.
Dosage to reach PF curtain resin ST: 0,75 %
Excellent improvement in filament break-up time obtained. Capillary velocity remarkably affected. Best.
Surfactant 4 0,2; 0,4; 0,6 Elongation: 0,2
Efficient ST reduction, higher dosage possible.
Dosage to reach PF curtain resin ST: 0,29 %
Good improvement in filament break-up time obtained.
Capillary velocity remarkably affected.
Surfactant/
Defoamer 1
0,03; 0,05;
0,1; 0,2; 0,4; 0,6
ST reduced, CMC achieved: 0,40 %.
Dosage to reach PF curtain resin ST: 0,11 %
Excellent improvement in filament break-up time obtained. Capillary velocity remarkably affected.
Defoamer 1 0,03; 0,05; 0,10 No major effect on ST, some type of CMC obtained: 0,05 %.
Filament break-up time and capillary velocity slightly improved, some type of CMC obtained: 0,05 % Defoamer 2 0,03; 0,05; 0,10 No major effect on ST. Filament break-up time and capillary velocity poorly
improved. No differences between dosage levels.
Defoamer 3 0,03; 0,05; 0,10 ST slightly reduced with highest dosage. Filament break-up time and capillary velocity poorly improved. Slight differences between dosage levels.
Additive combinations were analyzed with extensional rheometer. Based on multiple linear regression (MLR) analysis results, surfactant/defoamer 1 was considered the best, since increased dosing was mainly important/reasonable in order to achieve desired elongational properties. Defoamer 3 was considered poor, since increased dosing was mainly not important. Defoamers 1 and 2 had relatively same type of performance. Surfactant 1 and 4 performances varied depending on the defoamers, the best combination was achieved with surfactant/defoamer 1 and other defoamers provided poor results. Surfactants 2 and 3 had relatively same type of performance, combination with all but defoamer 3 provided good results. Operational windows were calculated to surfactants 2 and 3 in combination with all defoamers. From the operational window, the additive dosage combination may be selected in order to achieve the desired elongational property, as long or longer break-up time than break-up time of PF curtain resin.