photoinitiated crosslinking of ethylene-vinyl acetate copolymers and characterization of related properties. - cross linked polymer
Ethylene-vinyl acetate (EVA)
Is made of ethylene and vinyl acetate (VA)
Excellent ozone resistance, weather resistance and excellent electrical properties .
EVA is a thermoplastic polymer widely used in different fields such as flexible packaging, footwear, hot adhesive, cable sheath, etc.
In order to improve the mechanical strength and heat resistance of EVA, the cross-linking of EVA is a useful method [3, 4].
It is reported that EVA elastic materials formed by cross-linking have excellent mechanical properties such as elastic modulus, hardness, toughness, tear strength and tensile strength .
At present, there are two main ways to cross-link EVA: High-
Energy irradiation ([. sup. 60]Co [gamma]-
Ray or electron beam)crosslinking [6, 7]
Chemical cross-linking (
Cross-linking of peroxide and silicone)[8-11].
Energy Radiation cross-linking is a key requirement for high input, complex operation and processing processes, safety and radiation protection.
Low heat in chemical methods
Due to the key conditions of cross-linking reaction, high efficiency, long cross time and complex processing requirements.
In recent years, there has been a major breakthrough in the photo
Initiation and cross-linking of bulk polyethylene (PE)[12, 13].
The mechanism and cross-linking structure of optical cross-linking of PE and its model compounds are reported in the literature [14-17].
At the same time, a kind of PE and its industrial UV-
The irradiation device has been developed and successfully applied to the manufacture of cross-linked PE (XLPE)
Insulated power cable]18, 19].
The main advantages of optical cross-linking are low cost of equipment, low energy consumption, simple operation and maintenance, high production efficiency, excellent electronic and mechanical properties.
As far as we know;
However, EVA light cross-linking caused by UV
Irradiation in the presence of photoinitiator has not been reported.
The optical cross-linking of EVA has a broad prospect in the industrial application of wire and cable.
In this paper, the optical cross-linking reaction parameters and optimal conditions of EVA are mainly studied, as well as the amount of heat by gel determination, thermal extension, differential scanning (DSC)
Dynamic Mechanical Thermal Analysis (DMTA)
Thermal weight analysis (TGA)
And mechanical measurement.
The ultimate goal is to use the optical cross-linking EVA for the manufacture of wire and cable.
The mechanism and cross-linking structure of optical cross-linking and photooxidation degradation of Eva will be reported in the following work.
Two kinds of EVA resin and an experimental material of low density polyethylene (LDPE)
Used in this study: EVA 14-
2 resin with a molten flow rate of 2. 5 g/10 min (EVA-
14 with 14 wt % VA)
Organic plant production in Beijing, China;
The melt flow rate is 3. 0 g/10min (EVA-
18 including 18% VA)
Produced by Samsung general petrochemical company, ldp2tn26 produced by China Qilu Petrochemical Company.
Six kinds of light initiator are benzone (BP)
Shanghai reagent factory number:1, China: 4-
Fluka AG from Switzerland; 4,4'-
Novakemi AB, Belgium;
And benzyl dimethyl Ketal (BDK),1-Hydroxy-cyclohexyl-phenyl-ketone (Irgacure 184), and2-hydroxy-1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (Irgacure2959)
From Ciba, Switzerland.
The four wearers are cyan acid salt (TAIC)
From Anhui College of Chemical Engineering, China;
Tripentyl alcohol triacrylic acid (PETA)
New pentyl alcohol diacrylic acid (NPGDA)
And three methanol triacrylic acid (TMPTA)
UCB from Belgium
All of the above chemicals are commercial products received.
Sample preparation all samples (
50g batch EVA, light initiator and chain quantity given)
Mix in 140 [8 minutes]degrees]Cwith an XSS-300 rheomixer.
After mixing, the sample is hot
Make a thin sheet of suitable thickness at 140 [lower pressure for 5 minutesdegrees]
Press it with a hot press.
Control plate thickness with a frame of 1mm thickness.
Preheating of sample irradiated to 140 [degrees]C and then UV-
Irradiatedin LC6B table conveyor equipped with F300SQ lamp system (
[D] bulb, light intensity 1800 mw /【cm. sup. 2])
Built by US Fusion UV system.
The distance between the F300SQ lamp and the surface of the sample is 5. 3 cm.
The irradiation time is controlled by the speed of the conveyor belt.
The atmosphere is generally [N. sub. 2]
Unless otherwise stated.
Measure the gel content.
After irradiation, cut the sample into slices and place it by 200-
Stainless steel mesh.
The gel content of the sample is determined by extracting the irradiated sample ([w. sub. 1])
Stabilize in a basket of 0 with boiling px for 48 h. 2% Tinuvin 144 (an antioxidant)
Bubbling [N. sub. 2]
The solvent was updated 24 hours after the first extraction.
After extraction, wash the basket with acetone.
After drying in a vacuum dryer of about 70 [degrees]
Heavy and refractory residues such as Insoluble ([w. sub. 2])was weighed.
Average gel content (wt%)
Calculate the as100 in the test ([w. sub. 2]/[w. sub. 1]).
Typically, three samples are analyzed to determine the average gel content under a given irradiation condition.
This method of measuring gel content has been shown to be feasible . Heat Extension. Dub-
The stress of the bell-shaped cross-linked sample is 0.
Keep the temperature at 200 [2 MPa in the oven]+ or -]1[degrees]C.
After 15 minutes of balance, the thermal expansion rate ([lambda])
Measured by the equation [lambda]= L/[L. sub. 0]-1, where [L. sub. 0]
Is the original length between the two marks on the sample before the thermal extension, and L is the actual length between the two marks after the thermal extension.
The effective cross-linking density can be calculated by equation : [upsilon]= [tau]/RT[1 + [lambda]-1/(1 + [lambda])[. sup. 2]]where [upsilon]
Effective cross-linking density of samples; [tau], the stress; [lambda]
Heat extension rate;
T, absolute temperature.
Differential Scanning heat
DSC measurements were performed on the Perkin Elmer Pyris I Heat Meter programmed for ahothold-cool-heat cycle.
Heating/cooling rate is 10 [degrees]
The temperature range of C/minand is 20-200[degrees]C with a 1-min hold time.
[Crystallization]X. sub. c]
Based on the ratio of the relative diffusion heat of each gram of sample to the melting heat of PE Crystal (287. 3J/g)
According to the literature .
Dynamic mechanical thermal analysis.
Perform DMTA on the aDMTA instrument (Perkin--Elmer--Pyris Diamond)
In a tensile mode with a frequency of 10Hz and a heating rate of 5 [degrees]C/min.
Thermal weight analysis
The TGA uses a ShimadzuTGA-
50 h thermal analyzer with scanning rate of 10 [degrees]
2 x C/min at air flow rate10. sup. -5][m. sup. 3]/min.
Measuring mechanical properties with universal testing machine (Instron 1185)
Temperature 25 [+ or -]2[degrees]C.
The speed of the cross is 25 mm/min. Dumbbell-
Shape sample prepared according to ASTM D412-87.
Tensile strength and breaking elongation were recorded.
Figure 1 shows the results and discussion features of light cross-linking formed by EVA gel
1 as a function of the irradiation time of sample polyethylene, EVA-14, EVA-
In the presence of BP and TAIC (1 wt%each).
It can be seen that the gel content of the sample increases rapidly with the increase of Irradiation time.
Gel content of about 72,82 and 88%, low density polyethylene, EVA-14, and EVA-18 samplesUV-
Irradiation of 5 s respectively.
The kinetic features of the cross-linking of the three samples have the same features :(1)
The initial cross-linking rate of the first 3 s is very fast; (2)
After 3 s, the rate dropped to a certain level; and (3)
The final gel content is almost constant. [
Figure 1 slightly]
However, it can be seen from the picture
1 There is a difference in the cross-linking rate of these three samples.
As the VA content of EVA in these samples increases, the gel formation rate increases.
This is due to the increase in the number of tertiary hydrogen in the EVAincrease chain as the VA content increases.
Tertiary hydrogen atoms can easily be extracted by light initiator BP to form a triple carbon free radical intermediate that binds to each other as cross-linked, as reported in our previous PE [Optical cross-linking work]14-16].
That explains why EVA
The rate and gel content of 18 samples were the highest, and the rate and gel content of low density polyethylene samples without VA were the lowest.
The effects of reaction conditions such as the concentration of photoinitiator and Delivery Agent, Irradiation Temperature and irradiation atmosphere on the light-induced cross-linking of EVA samples were studied. Photoinitiator.
Six different light initiator were selected and used in this work.
These light sponsors are divided into two groups:1)
Those who abstract hydrogen in the exit state (e. g.
BP and its derivatives)and (2)
Those who take picturesfragmentation (e. g.
, BDK, Irgacure 184, Irgacure 2959).
Figure 2 compares EVA-
18 samples containing 1 wt % initiator, no cross agent was added.
Obviously, the abstract hydrogen system of BP and its derivatives has better light-induced efficiency, and
Active initiator such as BDK, Irgacure 184 and Irgacure2959 appear to be inefficient in light cross-linking of EVA. [
Figure 3 shows the dependence of gel content on BP concentration for two EVA samples.
For both samples, the optimal concentration of BP is about 1wt % relative to EVA.
A further increase in the amount of photoinitiator does not increase the gel content.
Samples of 2 wt % BP showed a lower gel content.
This is interpreted as due to two effects.
BP of ground state and triple state absorbs ultraviolet rays in n-region[pi]
It can shield ultraviolet rays and act as a transition to the "vending machine.
In addition, some ketone-based radicals formed by photoinitiator will be combined with polymer radicals to prevent light-induced cross-linking of eva.
With the increase of bp concentration, both effects are expected to increase. [
Figure 3 slightly]Crosslinker.
Added a multi-function Cross
The addition of the Chain Home greatly speeds up the cross-linking process, and it is important to choose the right Chain Home.
Gel content of EVA
Figure 18 shows samples with four different cross joints and no cross joints4.
The combination of an available light initiator with multi-functional cross-linking agent can greatly promote the light cross-linking reaction.
Similar results have been observed in detail in previous work .
Looks like BP.
As shown in the figure, the TAIC optical trigger system is the most effective of the four cross connectors. 4.
This is due to the better solubility of the TAIC containing the anonyate group compared to PETA or tmta [and more evenly distributed in the polymer]23].
In addition, taic also promotes the deeper penetration of cross-linking in olefin, thus improving the optical cross-linking efficiency [23, 24].
The effect of TAIC concentration on gel content is shown in the figure. 5.
The results show that 1 wt % TAIC is the best amount for gel formation.
Further addition of TAIC will only have a small impact.
Even under 2wt % TAIC, EVA-
Reduction of 14 samples.
This indicates that too much TAIC can form a lowmolecular-
Average weight polymer 
It is easy to extract with px.
Therefore, the TAIC homopolymers reduce the cross-linking between TAIC and EVA, resulting in a decrease in gel content.
Figure 6 shows the change of gel content of two EVA samples with the increase of irradiation temperature.
It can be seen that the gel content increases with the increase of irradiation temperature.
This can be interpreted as two factors.
With the rise of the radiation temperature, there is more free volume in EVA.
Free volume provides enough space for the movement of the polymer chain in a relatively long segment.
In addition, the movement rate of the polymer segment increases with the increase of irradiation temperature.
These two factors accelerate the molecular movement of the polymer chain, thus speeding up the binding between molecules and forming a cross chain. [
Figure 4 slightly][
Figure 5 Slightly]
Influence of irradiation atmosphere ([N. sub. 2]or air)
Study on formation of EVA gel
Sample shown in Figure 18. 7.
It is clear that oxygen in the air inhibits the cross-linking process.
The gel content of the irradiated sample in air was reduced by about 5% compared to the sample irradiated in [N. sub. 2].
The effect of oxygen on the light cross-linking of EVA samples is due to the addition of oxygen in chemical intermediates, which can compete with the cross-linking reaction through free radical binding, thus reducing the gel content.
Although oxygen does inhibit the cross-linking process, the effect is small (
A few percent of gel content).
This is understandable because the exposure time is very short.
Only a few seconds)
And the ability of oxygen to enter the sample (thick 1 mm)is low. [
Figure 6 slightly][
Figure 7 Slightly]
The heat extension can quickly determine the cross-connection density of the sample.
Data on thermal extension of optical cross-linking EVA-and corresponding cross-linking density
18 samples are listed in Table 1.
It was found that the unirradiated sample failed to pass the test immediately.
Samples irradiated for 1 and 2 s still failed to pass the test but remained for a few minutes.
However, the thermal elongation of the sample UV-
Irradiation above 3 s was tested.
Thermal extension value of optical cross-linking EVA
As the irradiation time increased from 3 seconds to 5 seconds, 18 samples were reduced from 58% to 107%.
EVA-corresponding cross-linking density
18 samples irradiated 3 to 5S were increased to 4. 31 x [10. sup. -5]mol/[cm. sup. 3]from 2. 77 x [10. sup. -5]mol/[cm. sup. 3].
Higher cross-linking density makes the thermal extension rate of cross-linked polymer at 200 [lower]degrees]C.
The melting temperature is listed in Table 2 ([T. sub. m])
Crystal degree of various optical cross-linking eva18 samples.
It can be seen that ,[T. sub. m]
The value of the EVA sample is from 84. 4[degrees]
The Cof of the unphotolinked sample is 82. 2[degrees]
C of the sample irradiated by 5 s.
Reduce words]T. sub. m]
Because the concentration of the length segment suitable for Crystal is reduced .
The Crystal degree of the light cross-linked EVA sample calculated according to the thermal fusion data decreased slightly with the increase of Irradiation time, from 10.
5% unirradiated samples to 9.
Sample irradiation of 0% for 5 s.
Figure 8 shows the change of the loss tangent (tan [delta])
Temperature of EVA-
18 samples irradiated at different times.
Location of Tan [delta]peaks at -5[degrees]
C corresponds to the glass deposition temperature of the EVA sample, with UV-
It can be observed from unirradiated EVA samples marked with solid lines, tan [delta]
Month of Shoulderpeak-50[degrees]
C, it is named therigid amorphous fraction, representing a part of the amorphous phase in the EVA Crystal, while the increase in tan [delta]near100[degrees]C for un-
The light cross-linked EVA sample may be due to the aging of the sample, as reported in the peroxide cross-linking of EVA [27, 28].
However, Tan [delta]
The UV peaks disappeared.
This means that the optical crossover further reduces the crystalline degree of EVA.
The intensity of Tandelta]
Peaks can be used for quantitative analysis of polymer amorphous phases.
It can be seen from figs.
8 The Tan [delta]peak height (at -5[degrees]C)
The number of samples irradiated by 5 s increased to 0. 24 from 0.
For unirradiated samples, this indicates a slight increase in the amorphous phase in EVAsample after light cross-linking.
Figure 9 shows the energy storage modulus (G')
Curves of light cross-linked EVA samples irradiated at different times.
With the increase of Irradiation time, especially at the starting temperature-75[degrees]C.
This is because, as reported in the literature [cross-link network structure enhances the storage modulus]29].
Thermal stability Figure 1 shows the thermal degradation behavior of samples monitored by tga10.
As can be seen from the TGA curve of figure 1.
Thermal degradation of EVA
18 samples can be obtained in two steps.
The first degradation step of 250420[degrees]
The C temperature range can be assigned to the evolution of acetic acid, while at 425-550[degrees]
The C temperature range is due to the degradation of ethylene chains in EVA.
It can be found from the dtg curve in figure 1.
The degradation temperature of samples irradiated 1, 3 and 5S by 10B is about 8-25[degrees]
C higher than 4384[degrees]
By comparing the pyrolysis temperature peaks of the response on the DTG curve, C of the unirradiated EVA sample.
Such as 463 pyrolysis temperature. 5[degrees]
The C of the sample irradiated by 5 s is 25. 1[degrees]
C is higher than the unirradiated sample.
These results show that optical cross-linking of EVA can significantly improve the thermal stability.
Figure 11 shows changes in the mechanical properties of EVA-
18 samples with different irradiation time.
It can be seen that the value of tensilestrength has increased sharply from 18.
4 MPa to 26 of unirradiated EVAsample.
Samples of irradiated 5S were 7 MPa.
This can be attributed to an increase in cross-linking density in cross-linked samples.
Therefore, the TS of EVA samples can be improved by light cross-linking.
However, the corresponding data of fracture elongation is 1530%-
SUV after 5 930%-irradiation.
This is because the network structure of cross-linking makes the polymer harder. [
Figure 9 omitted[
Figure 10 slightly][
Figure 11 omitted]CONCLUSIONS 1.
Optical cross-linking is an effective method of EVA cross-linking.
A light-induced system involving a combination of suitable initiator and multi-functional linker such as BP-
TAIC can effectively promote the light cross-linking reaction.
Irradiation Temperature and VA content of EVA are essential to improve the light cross-linking rate of EVA samples, except for BP-
An enhanced light trigger system for Taic. 2.
The data of thermal extension and DSC determination showed that the cross-linking density of light cross-linked samples increased with the increase of Irradiation time, however, with the increase of Irradiation time, the Crystal degree and melting temperature of cross-linked samples are reduced because cross-linking affects the accumulation of large molecular chains in the lattice, resulting in smaller and more disordered crystals. 3.
The TGA results show that the optical cross-linking of EVA can improve the degradation temperature of EVA material and enhance its thermal stability.
At the same time, mechanics and DMTAdata also show that light cross-linking can improve the tensile strength and storage modulus of high-gloss cross-linking eva, but does not change the loss tangent (tan [delta])
Represents the temperature through the glass ([T. sub. g]).
DMTA determination also showed that optical cross-linking increased the fraction of EVA non-crystalline phase, which was consistent with the reduction in the crystalline degree obtained by DSC. 4.
By optimizing the parameters such as the concentration of reaction ofphotoinitiator and cross-linking agent, the irradiation time, and selecting ofsuitable resin, EVA sheet thickness up to 1mm months can easily be irradiated and cross-linked, in short-term --
5 s with satisfactory cross-linking degree above 80% gel content.
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Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei 230026, Anhui province, Hefei, Anhui province, China, Hongda Yao, Baojun district, communication author: Wu Qianghua; e-Email: qhwu @ ustcedu.