Effect of High Density Polyethylene (HDPE) on Structural and Optical Properties of (PP/PMMA) Blends

. In the present work, Polypropylene (PP) was blended with poly methyl methacrylate (PMMA) to form (PP/PMMA) polymer blends. High Density Polyethylene (HDPE) was mixed into these blends at different weight fractions (2,4,6,8) % wt to form (PP/PMMA/HDPE) blends were prepared using an one screw extruder. results obtained from Scanning Electron Microscopy (SEM) revealed that there was a reduction in surface roughness any decrease in clusters, drilling and bends, as for Fourier Transform Infrared (FT-IR) spectrometry showed no change in the wave numbers of the functional groups. The optical properties of samples are investigated by measuring optical absorption spectra in the wavelength range from 260 to 1100 nm. this results show that E g of the blends increases with increasing high density polyethylene contents, the indirect optical band gaps for (PP/PMMA) and (PP/PMMA/HDPE) blends were estimated to be about 2.83,2.9,2.95,3and 3.1 eV for indirect allowed transitions, whereas the indirect forbidden band gaps were determined as 2,2.1,2.15,2.2 and 2.3 eV with increase high density Polyethylene contents, respectively. The absorbance, absorption coefficient, extinction coefficient and the imaginary dielectric constant of (PP/PMMA/HDPE) decreases with increasing of HDPE percentages except the transmittance, refraction index and real part of the dielectric constant increase with increasing of high density polyethylene.


INTRODUCTION
Polymer blend represents very important field in processing of new materials which has better properties in comparison with the net polymers. They are significant also from ecological and economical viewpoint [1]. Therefore the polymer blend can be defined as the mixture which has no covalent bonds between components [2]. Polymer blends can be characterized by their phase behavior as being either miscible or immiscible. Immiscible blends show multiple amorphous phases while the miscible blend has only one amorphous phase [3]. Polypropylene (PP) is one of the most important commodity polymers and is used in many areas, such as home appliances, automotive parts, construction and other important industrial applications. PP's applications are often limited due to its low impact strength and Young's modulus properties, particularly at low temperatures and high temperature loading conditions. Blending PP with different polymers is an economic and effective way to improve these drawbacks [4,5]. Polymethyl methacrylate is highly transparent plastic with good mechanical strength and is used variously from commodities to industrial applications. Accordingly, the PMMA is a candidate substrate for optical and medical applications [6,7] as bone cement, dialyser, scaffolds for tissue engineering and potential candidate to waveguide production [8]. The polymer has very good optical properties but has poor scratch resistance. It has good dimensional stability due to rigid polymer chains. It has good weather resistance, and is stable to acid and alkalis. It is attacked by several organic solvents, and has good impact strength higher than that of glass or polystyrene [9]. It has the best transparency and optical properties of commercially available thermoplastic. It is colorless with a 92% light transmission, an index of refraction of 1.49. It comes in a full range of transparencies. Some of its applications are lenses, outdoor lighting, and indoor lighting [10,11]. High density polyethylene (HDPE) is the highest-volume polymer in the world [12]. HDPE resins have linear molecular chains with comparatively few side chain branches, the chains are packed more closely together. The results are crystalline up to 95 percent and densities ranging from (0.94 to 0.96) g/cm 3 [13].

Preparation of (PP/PMMA/HDPE) Blends
The Preparation of polymeric mixtures have been using an one screw extruder. The extrusion method was used to different sample prepare which includes polymeric grained smelting and converted to homogeneous fusible by mixing and heating, Then pumping the molten Through the configuration nozzle "Die" to structures formation with cylindrical shape, thereafter cooled by water basin. The extrusion zone temperature ranged from 210 to 250 ᵒ C and a screw speed of 13 rpm was used (the mixing time is less than 40 min. After that, samples cutting in engineering workshop the samples of thickness (2mm) and diameter (2.5cm).

Theoretical
The relationship between incident intensity and penetrating light intensity is given by Equation1 [14]: Where t t is the thickness of matter (cm) and α is the absorption coefficient (cm -1 ).

log
The absorption coefficient can be calculated by: If the amount of absorption is (1 cm -1 < α < 10 4 cm -1 ), the electronic transitions are indirect. The amount of optical energy gap from this region can be evaluated by the relation [15]: Where hv is the photon energy, B is the proportional constant, E g is the allowed or forbidden energy gap of indirect transition, +E ph is the emission or absorption phonon energy and r is a constant.
The complex refraction index consists of real and imaginary parts: The relation between reflectivity and refractive index is given by Equation [16]: If (kₒ =0) [17] n = The extinction coefficient can be calculated by using Equation [18]: Where λ is the wavelength of the incident ray.

International Letters of Chemistry, Physics and Astronomy Vol. 60
The relation between the complex dielectric constant and the complex refractive index (n * ) is expressed by: ε r = (n * ) 2 (10) It can be concluded that [19]: The real and imaginary complex dielectric constant can be expressed by Equations 12 and 13 respectively:

Scanning Electron Microscopy (SEM)
SEM images were taken to study the morphology of (PP/PMMA) blends with or without HDPE and compatibilizer. The measurements demonstrated a high degree of interoperability between the polymeric mixtures. Figure (1-a) show that the basis material its density random spread, leading to the emergence of clusters, drilling and bends heterogeneous, but when adding a few concentrations of high-density polyethylene to mix observe a decrease in surface roughness any decrease in clusters drilling and bends, and it attributed the decline because of the structural nature of linear chains consisting of (HDPE) [20,21]. This can be seen clearly decreasing at successive concentrations (2,4,6,8)

FT-IR spectroscopic analysis
FT-IR spectroscopy has been used to analyze the interactions among atoms or ions in (PP/PMMA/HDPE) blends. These interactions can induce changes in the vibrational modes of the blends. Figures (2,3,4,5 and 6) represents the FT-IR spectra of (PP/PMMA/HDPE) respectively, in the wave number range (500-4000) cm -1 .In case of pure (PP/PMMA) figure (1), absorption packs sites show at (2950.32-2851.19) cm -1 is assigned to C-H stretching vibrations indicating the presence of methylene and methyl groups, the wave number 1743.61cm -1 correspond to C=O stretching vibrations Of acetyl groups. but regarding absorption band at 1375.78 cm -1 arises due to Bending vibrations of C-O groups and the absorption band at 1255.97 cm-1 . It has been attributed to bending vibrations of C-O groups [22,23,24]. The Fourier transforms infrared spectra of (PP/PMMA/HDPE) blends, with different ratio of HDPE are shown in figure (3,4,5 and 6). From the infrared spectra, it can be noticed that the variation of HDPE ratio causes some observable changes in the spectrum of (PP/PMMA/HDPE) within the same range of the wave number. It induces some new absorption bands and slight changes in the intensities of some absorption bands. The new absorption bands may be correlated, likewise to defects induced by the charge-transfer reaction between the polymer chains. This indicates the considerable not interaction between the three polymers.  (7) shows the absorbance spectra as function of the wavelength of the incident light for (PP/PMMA/HDPE) blend with different concentration of HDPE. It is clear that increasing the concentration of HDPE in the polymer blend leads to decreasing the peak intensity, and there is no any shift in the peak position for all amounts of the added material to the blend, that means there is no chemical interaction when added HDPE to the matrix and the decrement in the absorption is attributed to the decrement offshoot and tangles of polymeric chains, The fact that the linear high density polyethylene (unbranched) [25,26].   The absorption coefficient (α) is calculated using equation (4). Figure (9) shows the absorption coefficient as a function of the photon energy, it can be noted that absorption is relatively small at low energy. This means that the possibility of electron transition is low, because the energy of the incident photon is not sufficient to move the electron from the valence band to the conduction band ( hυ<E g ). The value of absorption coefficient is less than 10 4 cm -1 at low energies, it is expected that indirect transition of electron occurs [28].   (11),we see that the values of energy gap increase with increase of the weight percentage of HDPE. This was due to the decrease of the site levels in forbidden indirect energy gap between the valence and conduction bands. It leads to increase the width of the optical energy gap with the increase in the concentration of highdensity polyethylene [29,30].   The change of extinction coefficient as a function of wavelength is shown in Figure (13). It was noted that (kₒ) has lower value in the ultraviolet region and large increase in the visible spectrum region and lasts until the spectrum near-infrared region, the extinction coefficient decrease with increase in concentration of high-density polyethylene, and this is attributed to decrease in the absorption coefficient. The real dielectric constant behavior with wavelength and change the added concentration shown in figure (14), have the same behavior for refractive index (n) and that depends on (n) according to equation (12) where very few extinction coefficient than refractive index can be neglected. but the imaginary dielectric behavior with wavelength and change the concentration of high-density polyethylene shown in figure (15). It is similar to the extinction coefficient and refractive index, the imaginary dielectric depends on (k) and (n) according to equation (13

CONCLUSIONS
In this study, scanning electron microscope image analysis showed the blends of (PP/PMMA/HDPE) have a high degree of compatibilizer. FT-IR scanning of the blends showed no change in the wavenumbers of the functional groups, which support the formation of (PP/PMMA/HDPE) physical blends, as well as the energy gap of indirect allowed and forbidden transition increases with increasing the concentration of high density Polyethylene, finally real dielectric constant increasing with increase the concentration of high density Polyethylene, but the imaginary dielectric constant decreases with increasing added.