In this research, recycled-polyethylene terephthalate (PET) and polycarbonate (RPET/PC) blends fabricated by vented barrel injection molding were presented to better understand the effect of devolatilization during molding process. The effect of dried pellets, non-dried pellets, using an opened-vented hole, and using a closed-vented hole on the miscibility, morphology, thermal properties and mechanical properties of RPET/PC blends was investigated. The results indicated that no drying decreases dispersion, thermal properties, and mechanical properties of RPET/PC blends due to hydrolysis degradation of recycled-PET during the injection molding process. Using the venting system with non-dried RPET/PC blends partially improves dispersion, thermal properties and molecular weight of RPET/PC blends processed without drying, giving results that are similar to those processed with drying. Regarding the flexural properties, using the venting system without drying prevents the flexural properties from decreasing in RPET/PC blends, if the amount of RPET is less than 75 wt%. When the content of RPET is over 75 wt%, using the venting system does not eliminate the decrease in flexural properties of RPET/PC blends. When the venting system is applied to non-dried RPET, despite hydrolysis degradation of RPET not being completely eliminated, the damaging effects are nonetheless reduced compared with those samples processed without the venting system. As a result, vented barrel injection molding hardly prevents non-dried RPET/PC blends from having reduced flexural properties when the content of RPET is greater than 75 wt%.
The most important commercial polyester polymer is polyethylene terephthalate (PET), which is widely used because of its high mechanical properties, high transparency, and low cost [
Srithep et al. [
As both PET and PC are hygroscopic and they are sensitive to any moisture content that is present. Thus, these materials need to be thoroughly dried before processing, and expensive drying hoppers are required to eliminate any moisture which might be occurred during the process [
In this research, the effect of moisture content and using the vented hole of the vented barrel injection molding on the mixing efficiency of RPET/PC blends was investigated, and RPET, PC and RPET/PC blends were fabricated by the vented barrel injection molding. The effect of dried pellets, non-dried pellets, using an opened-vented hole, and using a closed-vented hole on the miscibility, morphology, thermal properties and mechanical properties of RPET/PC blends was investigated. The advantages of vented barrel injection molding on the mixing efficiency of RPET/PC blends under varying processing conditions are presented.
Recycled poly(ethylene terephthalate) (RPET) with intrinsic viscosity of 0.65 dl/g and molecular weight of 12,600 g/mol was supplied by Negoro Sangyo Co., Ltd., Japan. Polycarbonate (PC) with melt flow index of 15 g/10 min (Iupilon® S-3000) was supplied by Mitsubishi Engineering-Plastics Corporation, Japan. The weight ratios of RPET: PC blends were varied at 100:0, 75:25, 50:50, 25:75 and 0:100. The dumbbell samples were dry-blended and fabricated by the vented barrel injection molding machine (TI-30F6, TOYO MACHINERY & METAL CO., Ltd.). A schematic of the vented barrel injection molding machine is shown in
The specimens were fabricated under four different operating conditions: dried pellet with opened-vented hole (D-V), dried pellet with closed-vented hole (D-NV), non-dried pellet with opened-vented hole open (ND-V) and non-dried pellet with closed-vented hole (ND-NV). The moisture content of RPET and PC
pellets before and after drying in an oven was evaluated by a Karl Fisher testing machine. The moisture content of the non-dried RPET and PC was 0.26% and 0.084%, respectively. After drying at 115˚C for 12 h, the moisture content of RPET and PC was 0.008% and 0.005%, respectively.
The observation of phase morphology was performed by a scanning electron microscope (SEM, JEOL/JSM-5200), which was set at 15 kV. Gold was sputtered onto the specimens for electron conductivity. The size of the dispersed phase was measured by using the image-J program with the SEM photographs. About 400 particles were measured to determine the diameter of the PC droplets. The average surface diameters were calculated as follows with Equation (1) [
D z ¯ = ∑ N i D i 2 ∑ N i (1)
The dynamic mechanical properties were performed on a DMA2980 (TA Instruments, USA) using single frequency strain and dual cantilever modes. The DMA was operated under atmospheric conditions at a constant frequency of 1 Hz. The specimens were heated from ambient to 180˚C with a heating rate of 3˚C/min.
Differential scanning calorimetry (DSC2920, TA Instruments, USA) was used to characterize thermal properties and crystallinity. Specimens weighing 5 mg were cut from the dumbbells and placed in an aluminum pan. The temperature was set from 30˚C - 300˚C with a heating rate of 10˚C/min under nitrogen atmosphere. The crystallinity of the RPET polymer was calculated from the following Equation (2);
X c ( % ) = ( Δ H m − Δ H c c ) × 100 Δ H f 100 × 1 W p (2)
where Xc is degree of crystallinity (%); ΔHm is enthalpy of melting enthalpy; ΔHcc is enthalpy of clod crystallization enthalpy; ΔHf100 is the heat of fusion of 100% PET crystallization (140 J/g [
For flexural testing, the specimens were cut to dimensions of 60 × 10 × 3 mm (length × width × thickness) from the dumbbells and the testing speed was 3 mm/min with a support span length of 48 mm according to ASTM D 790.
Gel permeation chromatography (GPC) were performed, which recorded on a system comprised of a Shimadzu (Kyoto, Japan) LC-20ADVP HPLC pump and a Shimadzu RID-10A differential refractive index detector. Two Showa Denko (Tokyo, Japan) Shodex GPC HFIP-806M columns with a Showa Denko Shodex GPC HFIP-LG guard column were installed in the system, and hexamethylene isopropanol (HFIP) was used as the eluent. The measurements were carried out at 40˚C at a flow rate of 0.6 ml∙min−1. Poly(methyl methacrylate) (PMMA) standards were used to calibrate the molecular weight ranging from 1,500,000 to 1310 Da. PC was conducted by a system comprised of Shimadzu GL science with SHIMADZU GPC-802C column. The measurement was done at a flow rate of 1 ml∙min−1. Polystyrene (PS) standards were carried out to calibrate the molecular weight ranging from 650,000 to 2200 Da.
The morphology of RPET/PC blends fabricated by the vented barrel injection molding was investigated by scanning electron microscopy (SEM). SEM photographs for all RPET/PC blends under the four different conditions are presented in
Many researchers revealed that the droplet morphology is generally found in a binary structure at a larger composition range, such as in COC/POE blends and PP/PC blends as revealed by Khonakdar et al. [
When comparing the SEM photographs of RPET/PC blends under each conditions, it is evident that non-dried RPET/PC blends with closed-vented hole (ND-NV) is the worst distribution of RPET or PC minor phase.
To verify the effect of drying and opening the vented hole, the size of the dispersed PC droplets in 25% PC were measured by Image-J software, and then the average surface diameter of 25% PC at various processing conditions was calculated. The cumulative percentage of droplets sizes and the calculated average surface diameter are shown in
The effects of drying and opening the vented hole on dynamic mechanical properties of RPET/PC blends were verified by Dynamic Mechanical Analysis (DMA). DMA is the useful technique, which the effect of dispersion and interfacial interaction can be effectively detected, especially by observation at the measured storage modulus [
Tan delta plots are shown in
The lower intensity of the tan delta peaks indicates better dispersion of the dispersed phase in RPET/PC blends [
delta peaks of the RPET/PC blends is noticeably decreased compared to those of neat RPET and PC, which indicates the existence of good dispersion in the blended RPET, or that PC restrained the molecular mobility of the polymer matrix during transition. In
Sample | Xc (%) | Tg RPET (˚C) | Tg PC (˚C) | Tcc (˚C) | Tm (˚C ) | |
---|---|---|---|---|---|---|
0% PC | ND-NV | 13.9 | 71.2 | - | 122.2 | 255.3 |
ND-V | 13.9 | 73.5 | - | 125.1 | 254.4 | |
D-NV | 12.2 | 74.2 | - | 126.8 | 252.6 | |
D-V | 12.0 | 74.5 | - | 127.3 | 253.3 | |
25% PC | ND-NV | 14.9 | 72.5 | Un | 125.4 | 254.5 |
ND-V | 14.3 | 73.3 | Un | 124.0 | 253.4 | |
D-NV | 11.9 | 75.6 | Un | 132.7 | 251.7 | |
D-V | 13.8 | 75.4 | Un | 130.9 | 251.2 | |
50% PC | ND-NV | 16.8 | 72.7 | 145.4 | 123.2 | 254.2 |
ND-V | 13.7 | 74.1 | 146.9 | 126.8 | 253.7 | |
D-NV | 9.8 | 77.8 | Un | 136.6 | 249.1 | |
D-V | 9.4 | 76.8 | Un | 137.4 | 251.3 | |
75% PC | ND-NV | 13.9 | 74.8 | 146.5 | 124.6 | 254.2 |
ND-V | 13.2 | 78.3 | 147.8 | 124.9 | 253.7 | |
D-NV | 11.8 | 78.1 | 148.3 | 134.6 | 250.7 | |
D-V | 8.0 | 78.1 | 148.4 | 134.4 | 251.0 | |
100% PC | ND-NV | - | - | 150.6 | - | - |
ND-V | - | - | 151.0 | - | - | |
D-NV | - | - | 150.6 | - | - | |
D-V | - | - | 150.8 | - | - |
Un: Untraceable.
of Tg for PC significantly decrease in the RPET/PC blends. The values of RPET’s Tcc for RPET and the blends show a similarly trend to the values of Tg. Tg and Tcc values of RPET and RPET/PC blends decrease when they are processed with no drying; however, the decrease in Tg and Tcc values of those made with no drying can be reduced by opening the vented hole. RPET and RPET/PC blends with no-drying, gives a higher degree of crystallinity of RPET when compared to those with drying, as shown in
From the flexural tests, load-displacement curves are shown in
The number average molecular weight (Mn), the weight average molecular weight (Mw), and the polydispersion index (PDI) of RPET and PC in both as-received and injection-molded samples at various conditions obtained by GPC are provided in
Samples | Mn | Mw | PDI |
---|---|---|---|
As-received RPET | 7650 | 12,500 | 1.63 |
RPET ND-NV | 4180 | 6680 | 1.60 |
RPET ND-V | 5540 | 8680 | 1.57 |
RPET D-NV | 7420 | 12,100 | 1.63 |
RPET D-V | 7320 | 12,000 | 1.63 |
As-received PC | 21,500 | 50,000 | 2.34 |
PC ND-NV | 21,200 | 46,300 | 2.18 |
PC ND-V | 22,000 | 48,600 | 2.13 |
PC D-NV | 22,800 | 48,400 | 2.18 |
PC D-V | 22,800 | 49,700 | 2.14 |
molecular weight of RPET in both D-NV and D-V RPET. On the other hand, performing injection molding with no drying in ND-NV decreases the Mw of RPET up to 47% as compared to the as-received RPET. When the vented hole is open, Mw of RPET ND-V decreases less than that of RPET ND-NV. The molecular weight of ND-V RPET decreased by 30% compared to the as-received RPET. On the other hand, in the case of PC, the molecular weight in ND-NV is reduced by 7% compared to the as-received PC. Opening the vented hole with non-dried PC (ND-V) yields a Mw that is very similar to that of the as-received PC. From the results, it is clear that hydrolysis degradation has less of an effect on PC compared to RPET. The open vented hole exhibits sufficient performance to prevent the decrease in molecular weight of non-dried PC (ND-V). As a result, when the PC content of RPET/PC is high, using the vented hole can prevent any decrease in mechanical properties from hydrolysis degradation. However, the devolatilization efficiency of vented barrel injection molding has to be further developed to better prevent hydrolysis degradation of RPET during processing of RPET/PC blends.
The GPC results confirm the reason for the increase in crystallinity of non- dried RPET and the blends, which have a higher flexural modulus than those of D-NV. Non-drying leads to hydrolysis degradation, which decreases the molecular weight of RPET and RPET/PC blends and facilitates molecular chain arrangement. Moreover, previous research [
No drying decreases dispersion, thermal properties, and mechanical properties of RPET/PC blends due to hydrolysis degradation during the injection molding process. Using the venting system with non-dried materials partially improves dispersion, thermal properties and molecular weight of RPET/PC blends pro- cessed without drying, giving results that are similar to those processed with drying. Regarding the flexural properties, using the venting system without drying prevents the flexural properties from decreasing in RPET/PC blends, if the amount of RPET is less than 75 wt%. When the content of RPET is over 75 wt%, using the venting system does not eliminate the decrease in mechanical properties of RPET/PC blends. The open vented hole exhibits sufficient performance to prevent the decrease in molecular weight of non-dried PC. As a result, when the PC content of RPET/PC is high, using the vented hole can prevent any decrease in mechanical properties from hydrolysis degradation. When the venting system is applied to non-dried RPET, despite hydrolysis degradation of RPET not being completely eliminated, the damaging effects are nonetheless reduced compared with those samples processed without the venting system. As a result, vented barrel injection molding hardly prevents non-dried RPET/PC blends from having reduced flexural properties when the content of RPET is greater than 75 wt%. Thus, the operating conditions for vented barrel injection molding must be further studied to prevent hydrolysis degradation, as it concerns the processing of RPET/PC blends. The effect of barrel temperature at the positions before the vented hole of the vented barrel injection molding should be investigated in future studies for improving devolatilization.
Thodsaratpreeyakul, W., Uawongsuwan, P. and Negoro, T. (2018) Properties of Recycled-Polyethylene Terephthalate/Polycarbonate Blend Fabricated by Vented Barrel Injection Molding. Materials Sciences and Applications, 9, 174- 190. https://doi.org/10.4236/msa.2018.91012