الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 185 |  |  |
| | | from | 185 | | |
Abstract
Summary and conclusion
This work aims to prepare nanohybrids based on UV-curable Aliphatic Urethane Acrylate (AUA) and different loading levels (1, 2, and 3Wt. %) of clay such as Montmorillonite (MMT). Thin polymer films were prepared on glass and tin plate with these formulated solutions and cured under UV radiation. The prepared nanohybrids compounds were characterized using different techniques. The thesis consists of three main chapters.
Chapter 1: Introduction.
In which an outlook about the curing, types of curing, comparison of curing methods, surface coating and coating techniques was presented with a brief explanation of their properties and characterization. A literature survey for the previous studies carried out on the similar subjects was also introduced.
Chapter 2: Materials and methods.
Include complete description of the apparatus and instruments used in the study. It also explains the method of preparation and characterization of coating materials. The methodology of different tests on the prepared materials was also described.
Chapter 3: Results and discussion.
Which contain the results obtained and their discussion. The obtained results throughout this work can be presented through the following parts:
A. Effect of irradiation time on curing Urethane acrylate coating by ultra violet light (UV)
This part is carried out to study the effect of irradiation times of UV curable source on polyurethane acrylate. Hardness, adhesion, bending and swelling tests were taken to find out the tests curing time. The curing of coating films was carried out by using the standard UV mercury lamp at different irradiation times (10, 15, 20 and 30 min). The result showed that when the time of cured film increased from 10 to 30 min, the hardness increased from (3H → 6H) and adhesion increased from (1B → 3B). All films at different times pass bending and chemical resistance. So, the best cured time is chosen to be 30 min because of the best values of hardness, adhesion and the flexibility obtained after this period.
B. Performance of urethane acrylate oligomer by EB-curing
The coating formulations were prepared (60% urethane acrylate + 40% of di functional monomer (TPGDA)). The curing of coating films was carried out by using the EB-irradiation at different irradiation doses (5, 10 and 15 K Gy). The result showed that the pencil hardness of the PU coating was 2H at low dose (5KGy), but by increasing the irradiation dose to (10, 15KGy) the hardness of coating improved from 6H to 7H. The results also showed that moderate adhesion (2B) at high dose (15KGy), but at low doses (5, 10KGy) the crosslinked PUA gave high adhesion (4B). All cured panels of PU at different doses pass bending and pass chemical resistance. Thus, the best cured dose was chosen to be 10KGy at which the best hardness, adhesion and flexibility resulted.
C. Preparation and curing of the different formulations by UV irradiation
Three coating formulations based on polyurethane a crylate resin were prepared and cured by UV radiation to select the best mechanical characteristic of cured films. The formulations (oligomer/monomer) were prepared with different concentrations [60/40, 70/30, 80/20] by adding benzophenone as initiator with ratio 3Wt. %. The result observed showed that by increasing the concentrations of oligomer to monomer (60/40, 70/30, 80/20), the hardness is increased from (5H →9H) but the adhesion is decreased from (3B→1B). All concentrations were pass bending and chemical resistance (very good). So, the best concentration of (oligomer/monomer) is (60/40) because the hardness, adhesion and the flexibility is very good.
D. Organically modification of clay
The agglomeration of clay mineral in the polymer matrix was caused because of the incompatibility between hydrophilic clay and hydrophobic polymer. Therefore, the most important step is surface modification of clay to achieve polymer nanocomposites. Organoclay had been produced, by exchanging inorganic cations of clay (e.g., Na+ Ca2+) with organic ammonium cations, to improve the compatibility of clay with organic polymers. When layered clays are filled into a polymer matrix, either conventional composite or nanocomposite can be formed depending on the nature of the components and processing conditions.
1. Conventional composite is obtained if the polymer can’t intercalate into the galleries of clay minerals.
2. Intercalated nanocomposite, in which monolayer of extended polymer chains is inserted into the gallery of clay minerals resulting in a well ordered multilayer morphology stacking alternately polymer layers and the interlayer spacing is expanded, but the layers still bear a well defined spatial relationship to each other.
3. Exfoliated the layers of the clay have been completely separated and the individual layers are distributed throughout the organic matrix.
E. characterization
1. FT-IR characteristics
FTIR spectra were used to check the completion of polymerization reaction. The characteristic absorption bands for AUA and UV-cured PUA are present at 1719Cm-1, 1524Cm-1 and 1234Cm-1 confirming the formation of PUA network as these bands represent the stretching vibrations of C=O, N-H and C−N groups, respectively. Band at 3368 Cm-1 represents the free hydroxyl, −OH groups in the system. The appearance of C=C band at 1630 cm-1 and disappearance in UV-cured PU. The basic characteristic bands of nanoclays are 1020Cm-1 (Si−O stretching) and 917Cm-1 (AL−O bending). In case of modifying MMT with CTAB, several new bands appeared at 2921Cm-1, 2853Cm-1, 1573Cm-1, 1471Cm-1 and 1348Cm-1 representing the stretching vibrations of symmetric C−H, asymmetric C−H, NH2 stretching, CH3 and CH2 asymmetrical stretching and CH3 and CH2 symmetrical stretching, respectively. For PU and nanocomposite MMT, the IR spectra showed the presence of bands at 1719 Cm-1, 1524 Cm-1, and 1234 Cm-1 which confirm the formation of PUA network as these bands represent the stretching vibrations of C=O, N-H, and C-N groups, respectively. Finally, the band at 3368 Cm-1 and 2289 Cm-1 represent the free hydroxyl, –OH and isocyanates, –NCO groups in the system, respectively. All the characteristics peaks of clay and PUA were detected in the spectrum of PUA-organoclay nanohybrids, suggesting the formation of nanohybrids.
F. Morphology
1. X-ray diffraction (XRD) analysis
For the preparation of high-performance polymer nanocomposites, one of the significant variables is to achieve a homogeneous and uniform dispersion structure of intercalated or exfoliated nanoclay platelets in the polymer matrix. The diffraction pattern of the MMT showed an intense peak at 2Ө=4.6º. The XRD curves of PUA/MMT nano hybrids at 1Wt. %, 2Wt. % and 3Wt. % organoclay loadings showed a shift to lower side by 4º. Bragg’s equation (n λ=2d sin Ө) exhibited an inverse relationship between basal spacing d and Ө. Basal spacing d increased by 1Wt. %, 2Wt. % and 3Wt. % organoclay loading. This significant increase in the basal space confirms that the PUA chains have been intercalated into the sheets of the clay and increased the basal spacing of the sheets.
2. Transmission electron microscopy
The results showed that PUA chains are progressively intercalated into the galleries of organoclay. The nanocomposite samples with different concentration of clay (1Wt. %, 2Wt. % and 3Wt. %) showed the fully exfoliated nanoclay platelets to be homogeneously dispersed along with stacked silicate layers with increased intergallery distance throughout the resin matrix. These results demonstrate that the step of mixing process using the sonicator is effective for obtaining a high extent of exfoliation. Moreover, the strong hydrogen bonding between the carbonyl groups in the main AUA oligomers and the hydroxyl groups on the surface of organically modified MMT clay appeared to accelerate the molecular diffusion of the urethane acrylate into the intergallery space, resulting in well-dispersed clay platelets with a high degree of intercalation or exfoliation structure.
G. Thermal Stability
1. TGA experiments
Thermal stability of cured coating was investigated by thermo gravimetric analysis of the UV-cured coating film. TGA thermograms revealed that the decomposition of both pure polymer and the nanocomposites, undergo three steps in the degradation. The first weight loss occurred in the temperature range of 140-300°C is account to around 8 % weight loss, the second step from 300-400°C is account to around 47 % weight loss and the third step 400-500°C is account to around 38 % weight loss in PUA. It was found that PUA/MMT show better thermal stability than that of pure PUA. The degradation (Td10 %) at 10 % weight loss increased by about 10.6 ºC with increasing clay loading to 3Wt% and the degradation temperature (Td80 %) at 80 % weight loss increased about 73.8ºC with increasing clay loading to 3Wt. % . The incorporation of clay into the polymer matrix improves its thermal stability by acting as a superior insulator. Also, increased thermal stability is due to the good dispersion of nanoparticles in polymer-matrix and strong chemical interactions between nanoclay (Na-MMT) and the PUA matrix.
2. DSC experiments
The pure PUA exhibited a glass transition temperature (Tg) at 5.99ºC. With the addition of organoclay, the glass transition temperatures of PUA/MMT nanohybrids obviously increased to 6.74, 8.55 and 10.33 ºC for 1Wt. %, 2Wt. % and 3Wt. % of MMT, respectively. This is because of the strong interaction between the polymer and the nano dispersed silicate layers. The improvement of both the decomposition temperature and glass transition temperature of composites indicates that nanocomposition is an efficient way to increase the thermal stability of PUA. The higher Tg of the nanocomposites opens the possibility of more applications, which may involve higher processing temperature.
H. Comparative study between different concentrations of MMT in urethane acrylate cured by UV-irradiation
The physico-mechanical and chemical test results of the investigated PUA and PUA/MMT cured films showed that all the cured films increased in hardness and decrease in adhesion and impact. Moreover, all of them pass bending test without any damage. On the other hand, chemical resistance results showed no remarkable defects for all cured films when immersed in acid and alkali. The increase in the crosslinking of cured films is due to the intercalations of polyurethane of acrylate between the layers of organically modified clay.
I. Comparative study between different concentrations of MMT in urethane acrylate cured by EB-irradiation
All the cured films have increase in hardness and decrease in adhesion but not significantly. Moreover, all of cured film pass bending test without any damage and chemical resistance results show no remarkable defects when immersed in acid and alkali. Also, the films of PUA and PUA/MMT cured by EB process produced high crosslinked and a more uniform polymeric film. Generally, it was found that the chemical and mechanical properties of PUA and PUA/MMT cured films by EB are better than the cured films by UV.
J. Application of Surface coating of PUA/MMT on wood using UV–irradiation
The present work is taken to develop the physical and chemical properties of plywood surface by curing with UV radiation. Plywood composed of relatively thin layers or plies which affect the shape and permanent form of thin plywood panels. To make the adequate performance of plywood surface, it is necessary to treat by photocuring process. The basic structural component of wood is plant Cellulose (60-75%). The cellulose molecules of wood have a certain probability of involvement which depends on the radiation intensity. It is known that wood is the best construction materials for civil works, industries, household articles and inner panels etc.
K. Chemical and mechanical properties on wood
i. Pencil hardness
The study showed that PUA/MMT hybrids with 3Wt. % of organo clay had the highest hardness followed by hybrid with 2Wt. % of organoclay. Increasing the crosslink density of cured film by increasing the functionality of reactive monomers can help to enhance the hardness of coating, also the structure of the urethane acrylate oligomer gives hard cured film. The basic structural component of wood is cellulose and contain (OH) group. Urethane acrylate contain (NH) group so urethane acrylate with (OH) group in wood substrate formed hydrogen bond. After UV-curing formed strong chemical bond between PU/MMT and wood substrate so the hardness is increased.
ii. Adhesion Strength
Adhesion is the test where a certain force is applied to pull out the coating from the surface of a substrate such as plywood. The data showed that the adhesion on wood decrease by increasing the concentrations of MMT. All samples showed excellent adhesion properties.
iii. Stain resistance
Drops of staining agents were pipette out onto the coating surfaces and covered with glass cup to prevent evaporation. After specified time of contact, the staining agent was wiped off with tissue paper and cleaned with water and then coating surface was examined for discoloration or change in appearance if any. It was found that all coating composition showed excellent stain resistance against the staining agents taken for the test.
iv. Steam resistance
The samples were exposed to steam for 1 h and then they were examined for any visible changes on the coating surfaces due to steam. The study indicated that the all cured films at different concentration showed excellent steam resistance property.
v. Cigarette burn test
A lit cigarette was placed horizontally on the specimen for 1 min. The tested area was cleaned with water and suitable solvent and then examined. It was found that all cured films at different concentration of MMT did not perform satisfactorily against cigarette burns and suitable additives have to identified and incorporated in formulations to provide cigarette burn resistance to coatings.
L. Application on the plywood surface by EB-irradiation
The surface curing by electron beam (EB) attacked the C=C bond and initiated the crosslinking process. By EB radiation, electrons penetrating the substrate are able to generate radicals. Radicals form the substrate combined with radicals form the network, which led to improved chemical and mechanical properties by grafting at the substrate/coating interface. It was observed that the pencil hardness of the PUA coating was 7H, by adding different concentration of modified-MMT (1Wt. %, 2Wt. % and 3Wt. %) the hardness of coating improved and increased to (8H and 9H). The adhesion on wood of the PUA coating was 4B, where PU/MMT coatings at different concentration were slightly decreased to (4B and 3B). It was found that all coating composition showed excellent stain resistance against the staining agents taken for the test. The all cured films at different concentrations showed excellent steam resistance property. It was found that all cured films at different concentration of MMT did not perform satisfactorily against cigarette burns and suitable additives have to identified and incorporated in formulations to provide cigarette burn resistance to coatings.
M. Comparative study between induced irradiation by UV and EB on nanoclay coating formulation
An increase in the nano MMT content was found to accelerate the cure reaction and cure rate of the EB-curable acrylate system. The EB cured coatings were much harder than the UV coatings. This is due to the fact that EB curing process produced a more uniform polymeric film.
It is known that the moderate adhesion of EB curable coatings to PUA and PUA/MMT related to low flexibility most often due to the high crosslink density of the polymeric network. It was found that all cured panels of all formulations PUA and PUA/MMT in acid or alkali media did not defects for all cured films.