Crystallization Of HDPE Research Articles

Investigation of physical and rheological properties of LDPE/HDPE/thermoplastic starch biodegradable blend films

AbstractIn this work, low‐density polyethylene/high‐density polyethylene/thermoplastic starch (LDPE/HDPE/TS) films were prepared with different compositions to obtain environmentally friendly materials. LDPE/HDPE/TS blends, at ratios of 95:5:15, 90:10:15, 85:15:15, 85:15:20, 85:15:25, and 85:15:30, were processed into thin films by a single‐step single‐screw extrusion. Fourier transform infrared spectra and scanning electron microscopy (SEM) micrographs confirmed the immiscibility of matrices and TS in the blend. In the SEM images, relatively good surface adhesion between matrix and starch was observed due to the presence of HDPE and glycerol in blends at low TS content. Differential scanning calorimetry analysis depicted an increase in the percentage of crystallinity with increasing HDPE. Starch presence in the blend had a more pronounced effect on the crystallization of HDPE when compared to LDPE with the long chain branching. Water absorption of the samples decreased with increasing HDPE and increased with TS content. The rheological properties of LDPE/HDPE/TS blends were investigated before and after biodegradation. Results were fitted with well‐known rheological models to achieve more valuable data about the effect of the composition as well degradation condition on the blend property. By adding HDPE in the blends, rheological properties close to the neat LDPE were obtained for LDPE/HDPE/TS films in the melt state.

Polyethylene reinforced by biomimetic (polydopamine, tannic acid) modified magnesium oxysulfate whisker: Mechanical properties, thermal properties and flame retardancy

Two-dimensional magnesium oxysulfate whisker (MOSw) was modified by polydopamine (PDA) and tannic acid (TA) instead of the traditional inorganic flame retardants activated by silane coupling agent ( γ -methacryloxypropyltrimethoxy silane, KH570) such as Mg(OH) 2 and Al(OH) 3 . Differential scanning calorimeter (DSC) results showed that MOSw could act as heterogeneous nucleation for crystallization of HDPE, and further increased the initial crystallization temperatures of composites treated with PDA and TA. Dynamic mechanical thermal analysis (DMTA) showed that both the storage modules and loss modules of the composites with modified MOSw were significantly increased, which suggested the improved compatibility and dispersion between the modified MOSw and matrix. The tensile strengths of HDPE/MOSw@PDA composite and HDPE/MOSw@TA composite could be 118.0% and 121.2% higher than that of HDPE/MOSw@KH570 composite, and the corresponding impact strengths could be 124.0% and 111.2% higher, respectively. Compared to HDPE, the synergistic effect of PDA- MOSw and TA- MOSw (combustion heat through the dehydration of MOSw, gas-phase flame-retarded effect of MOSw, scavenging of active free radicals) increased the limit oxygen index (LOI) of composites from 19.4% to 23.4% and 23.8%, respectively, which were higher than 20.6% of traditional HDPE/Al(OH) 3 @KH570 composite with the same 30 wt.% filler. Schematic of self-polymerization of dopamine, and chelation of tannic acid with metal ions • MOSw covered with PDA and TA substituted for the traditional inorganic flame retardants activated by silane coupling agent. • Different from traditional inorganic flame retardants such as Mg (OH) 2 and Al (OH) 3 , MOSw modified by PDA and TA could not only improved the flame retardancy of HDPE, but also improved the tensile strength to a certain extent. • The composites with MOSw modified by PDA and TA showed good thermal stability.

Poly(butylene succinate)/high density polyethylene blend-based nanocomposites with enhanced physical properties – Selectively localized carbon nanotube in pseudo-double percolated structure

In this study, immiscible poly(butylene succinate)/high density polyethylene (PBS/HDPE) blend-based nanocomposites were successfully prepared through a melt mixing process. Carbon nanotube (CNT) and maleated HDPE (PEgMA) served as the reinforcing nanofiller and compatibilizer, respectively. Scanning electron microscopy images showed that PEgMA played an efficient compatibilizer role for reducing the dispersed domain size of HDPE in the PBS/HDPE blend. The added CNT was mainly selectively localized in the HDPE domains, leading to a pseudo-double percolated structure. Thermogravimetric analysis revealed that the presence of CNT evidently enhanced the thermal stability of HDPE phase in the composites. Differential scanning calorimetry results showed the nucleation effect of CNT on HDPE crystallization, whereas PEgMA accelerated the crystallization of PBS. The rigidity of neat PBS increased after blending with HDPE and then further increased after the formation of nanocomposites. The Young's modulus increased up to 50% compared with neat PBS in the 3 phr CNT-added composite. Measurement of the rheological properties confirmed the achievement of pseudo-network structure in the compatibilized blend and composites. The electrical resistivity of the blend drastically reduced, by up to 8 orders, when 3 phr CNT was added into the blend. The electrical percolation was constructed at a CNT loading of 0.6–1 phr.

Poly(Vinyl Alcohol) Fiber Reinforced High Density Poly(Ethylene) Composites: Melting and Crystallization Behavior

In the present study, high density poly(ethylene) (HDPE)/poly(vinyl alcohol) (PVA) fiber composites were prepared via melt blending technique using a co-rotating twin screw extruder (TSE). The effect of four different PVA fiber concentrations (i.e. 0, 5, 10, 20 wt%) on the melt and crystallization behavior of the HDPE/PVA fiber composites were investigated. The surface morphology of the composites was analyzed by a scanning electron microscopy (SEM). Whereas, the melt and crystallization behavior of the composites were analyzed by a differential scanning calorimetry (DSC). The SEM analysis on the cryo-fractured surface of the HDPE/PVA fiber composites exhibited that the PVA fibers were well blended/distributed in the HDPE matrix. Additionally, the DSC test results showed that the addition of PVA fiber in the HDPE matrix did not significantly change the melting peak temperature (Tm) of the composites. Furthermore, a slight decrease of the crystallization peak temperature (Tc) can be observed when the PVA fiber was incorporated in the HDPE matrix, which indicated a weak nucleation ability of the PVA fibers in the HDPE crystallization process. The same trend was also observed for the crystallinity index (Xc). The crystallinity index of the composites decreased with increasing PVA fiber loadings.

Hierarchical structure of MWCNT reinforced semicrystalline HDPE composites: A contrast matching study by neutron and X-ray scattering

Combining neutron and X-ray scattering (SANS, SAXS, and WAXD) as the contrast matching probes, the hierarchical structures of the multi-wall carbon nanotubes/high density polyethylene (MWCNTs/HDPE) composites (0.1–2.0 wt%) have been studied. SANS measurement avoided the correlation peak associated to the semicrystalline nature of HDPE from SAXS, and the passible scattering from the stretch induced voids. Benefitting from SANS data, the power law (α) taking the flexible cylinder suggested that whole MWCNTs in the unstretched composites follow a self-avoiding random walk (α ≈ 1.67). SANS data suggest a hollow flexible cylinder structure with outer and inner diameters (core-shell-like cross section) of the scatterers as ca. 12.6 nm and 4.1 nm, while the Kuhn length is about 43.0 nm. Tensile test displayed improved mechanical properties. Interestingly, the Hermans orientation parameter (f) of HDPE crystals (fc) in the stretched composites are around a plateau ca. 0.96 initially, while decreased remarkably to 0.776 when the fraction is further increased to 2.0 wt%. f obtained by SANS showed a similar tendency (decreased from 0.756 to 0.572). Combining all the results along with differential scanning calorimetry (DSC) measurement, a mechanism of adhered crystals on the surface of MWCNTs and a reinforcement model are proposed.

High‐density polyethylene/expanded graphite nanocomposites produced by polymerization‐filling technique using an industrial heterogeneous catalyst

ABSTRACTHigh‐density polyethylene nanocomposites with different expanded graphite (EG) contents (0.34–1.80 wt %) were prepared by polymerization‐filling technique using an industrial heterogeneous catalyst (cat K), and characterized using a range techniques: melting flow index (MFI), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and transmission electron microscopy (TEM). The MFI data showed that EG acts as a plasticizer decreasing melt viscosity in comparison to neat HDPE produced exclusively by cat K. DSC results showed that EG nucleated the HDPE crystallization as established by the increased crystallization temperature, and the degree of crystallinity. HDPE/EG nanocomposites displayed a significant improvement in the flexural (increased from 1458 to 1831 MPa), and storage modulus (increased from 122 to 1627 MPa) at only 1.80 wt % EG content. TEM images confirmed a homogeneous distribution of EG into the polymer matrix with the presence of dispersed, intercalated and aggregated EG nanofillers. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 55, 1260–1267

Composites based on green high-density polyethylene, polylactide and nanosized calcium carbonate: Effect of the processing parameter and blend composition

This paper describes the effect of composition and extruder screw rotation on the melt viscosity, degree of crystallinity, tensile properties and morphology of composites based on green high-density polyethylene (green HDPE), polylactide (PLA) and nanosized calcium carbonate (nCaCO3). A three-level central composite rotatable design was used to establish the composite formulation. The three factors studied were screw rotation (SR; 0–100 rpm), PLA content (0–35 wt %) and nCaCO3 content (0–5 wt %). The results showed that flow behavior of the composites depends on nCaCO3 content and SR. Polylactide and nCaCO3 levels influenced the development of green HDPE crystals, and the green HDPE matrix induced PLA dispersed phase crystallization. The solvent extraction method was efficient at revealing the morphologies of the composites, indicating a well distributed PLA dispersed phase in the green HDPE matrix. Additionally, nCaCO3 content contributed to reducing the particle domains of PLA by decreasing the interfacial tension between green HDPE and PLA. With respect to mechanical properties, the results showed that modulus of elasticity and tensile strength at yield are affected by PLA content.

Study on viscoelastic, crystallization, and mechanical properties of HDPE/EVA/Mg(OH)2 composites

In this article, elastomer‐toughened high density polyethylene/magnesium hydroxide (HDPE/MH) composites with various contents of ethylene vinyl acetate copolymer (EVA) are prepared in a twin‐screw extruder and then injection‐molded. The effect of EVA on the viscoelastic, crystallization, morphology, and tensile properties of the HDPE/EVA/MH composites is studied. The rheological behaviors show that the complex viscosity, storage, and loss modulus at low frequencies are largely unaffected with various EVA contents; however, the corresponding values decrease with increasing EVA content at high frequencies. The scanning electronic microscopy studies on the HDPE/EVA/MH composites show that the MH particles mainly disperse in the EVA phase, and the interfacial adhesion has been also enhanced due to the addition of EVA. The crystallization of HDPE diminishes because of the surface energy difference resulting in encapsulation structure. The tensile properties of the HDPE/EVA/MH composites are strong influenced by the incorporation of EVA. POLYM. COMPOS., 38:1221–1226, 2017. © 2015 Society of Plastics Engineers

Simultaneous Synchrotron WAXD and Fast Scanning (Chip) Calorimetry: On the (Isothermal) Crystallization of HDPE and PA11 at High Supercoolings and Cooling Rates up to 200 °C s(-1).

An experimental setup, making use of a Flash DSC 1 prototype, is presented in which materials can be studied simultaneously by fast scanning calorimetry (FSC) and synchrotron wide angle X-ray diffraction (WAXD). Accumulation of multiple, identical measurements results in high quality, millisecond WAXD patterns. Patterns at every degree during the crystallization and melting of high density polyethylene at FSC typical scanning rates from 20 up to 200 °C s(-1) are discussed in terms of the temperature and scanning rate dependent material crystallinities and crystal densities. Interestingly, the combined approach reveals FSC thermal lag issues, for which can be corrected. For polyamide 11, isothermal solidification at high supercooling yields a mesomorphic phase in less than a second, whereas at very low supercooling crystals are obtained. At intermediate supercooling, mixtures of mesomorphic and crystalline material are generated at a ratio proportional to the supercooling. This ratio is constant over the isothermal solidification time.

Non-isothermal crystallization kinetics of high density polyethylene/graphene nanocomposites prepared by in-situ polymerization

Abstract High density polyethylene/graphene nanocomposites were synthesized via in-situ polymerization technique using metallocene catalyst and methylaluminoxane (MAO) as co-catalyst. The non-isothermal crystallization of the nanocomposites was studied using differential scanning calorimetry (DSC). Modified Avrami, Ozawa and the model proposed by Mo et al. were applied in the analysis. The activation energy (ΔE) was calculated using the iso-conversional method proposed by Vyazovkin. The effect of degree of transformation and temperature on ΔE was analyzed. It was found that graphene nucleates the crystallization of HDPE by lowering ΔE as well as increasing the crystallization onset temperature (Ton). However, at later stages of crystallization, excess amount of graphene hinder the crystal growth rate thereby retarding overall rate of crystallization, observed from increase of t1/2 and degree of super cooling.

고밀도 폴리에틸렌/폴리에틸렌-옥텐 공중합체 블렌드의 결정화 거동 및 기계적 물성에 관한 연구

이 연구에서는 옥텐의 함량이 다른 4가지 메탈로센 LLDPE (mLLDPE)를 각각 HDPE와 여러 조성에서 혼합한 후 시료들의 결정화 거동 및 기계적인 물성을 관찰하여 mLLDPE/HDPE의 혼화성에 관하여 연구하였다. 옥텐의 함량이 4.1, 6.8, 9.8 및 12.5 mol.% 인 네 종류의 mLLDPE에 HDPE를 100/0, 80/20, 60/40, 40/60/ 20/80 및 0/100의 비율로 용융 혼합하여 시료를 제조하였고, 이 시료의 결정화 온도, 용융온도를 DSC를 이용하여 측정하였다. 또한 각 시료의 기계적 물성을 인장 시험기를 이용하여 측정하였다. HDPE와 mLLDPE의 결정화 온도 및 용융온도는 상대편 고분자의 존재에 의하여 변하는 것으로 보아 용융상태에서 두 물질이 서로 같이 존재하는 구조, 즉 완전히 균일상이거나 최소한 부분적 상용성이 있음을 알 수 있었다. 용융온도가 낮은 mLLDPE의 용융피크는 HDPE를 첨가함에 따라증가하는 것으로 보아 mLLDPE의 결정상에는 HDPE가 같이 결정화가 되어 있는 것을 알 수 있었다. 그러나 HDPE결정에 mLLDPE가 같이 결정화 되어있는지는 확인할 수 없었다. 열분석과 기계적 물성을 측정한 결과 HDPE와 mLLDPE의 상용성은 mLLDPE에서 존재하는 옥텐의 함량이 낮을수록 증가하는 것을 알 수 있었다. 【Compatibility between mLLDPE and HDPE was investigated by observing the crystallization behavior and mechanical properties of their blends. HDPE and mLLDPE blends were prepared by a melt-blending with compositions of 100/0, 80/20, 60/40, 40/60/ 20/80 and 0/100. Four different mLLDPEs containing various octene contents (4.1, 6.8, 9.8 및 12.5 mol.%) were investigated. The melting temperature and crystallization peak temperature of the blends were measured by DSC and the mechanical properties were measured in an universal testing machine. By observation that the melting and crystallization peak temperatures of one component were affected by its counterparts, it was revealed that HDPE and mLLDPE are miscible or at leat partially miscible at molten state. It was also found that the crystalline phase of mLLDPE contains HDPE crystals. However. it was not clear that mLLDPE was cocrystalized in the crystalline phase of HDPE. By various investigation with DSC and mechanical properties, it was concluded that the compatibility between mLLDPE and HDPE decreases with the octene content in the mLLDPE.】

Effect of Compatibilizers on Mechanical and Thermal Properties of High Density Polyethylene Filled with Bio-Filler from Eggshell

In this research work, the effect of compatibilizers on mechanical and thermal properties of ESP/HDPE composites was investigated. High density polyethylene grafted with maleic anhydride (HDPE-g-MA) and ethylene propylene rubber grafted with maleic anhydride (EPR-g-MA) were used to compatibilize the ESP/HDPE composites. The ESP/HDPE composite with and without the compatibilizes was prepared at 20 wt.% ESP. The volume average particle size of ESP was 20.35 µm. The compatibilized HDPE composites were prepared at 2, 5, 8 and 10 wt.% of HDPE-g-MA and at 2, 5, 8 and 10 wt.% of EPR-g-MA, as well. It was found that ultimate stress, yield strength, and elongation at break of the ESP/HDPE composites prepared with HDPE-g-MA increased with increasing HDPE-g-MA content. In addition, Young’s modulus was maximum at 8 wt.% HDPE-g-MA. The composites filled with HDPE-g-MA had improved impact strength with increasing HDPE-g-MA content. On the other hand, the composites with EPR-g-MA showed a decrease in tensile properties and impact strength when increasing EPR-g-MA content. The impact strength of the HDPE composites compatibilized with EPR-g-MA decreased with increasing EPR-g-MA content. In addition, degree of crystallinity of the composites with EPR-g-MA was higher than that of the composite with HDPE-g-MA. Furthermore, compatibilizing ESP/HDPE composites with either HDPE-g-MA or EPR-g-MA did not influence HDPE and ESP decomposition temperatures, HDPE melting temperature and HDPE crystallization temperature.

A Convenient Route to High‐Performance HDPE–CNT Conductive Nanocomposites by Control of Matrix Nucleation

AbstractWe show how styrene‐ethylene‐propylene‐styrene (SEPS) triblock copolymer uniquely reduces the electrical percolation threshold after matrix crystallization of conductive nanocomposites based on high viscosity HDPE with low amounts of pristine multiwall carbon nanotubes (CNT). Rheo‐dielectric and Flash DSC techniques are used to demonstrate that SEPS interferes with the nucleation ability of CNT on HDPE crystallization in a way that favors contacts between the nanotubes after crystallization as well as it improves CNT dispersion.

Non-isothermal crystallization behavior of Styrene butadiene rubber/high density polyethylene binary blends

The thermal and crystallization behavior of the blends are studied by differential scanning calorimetry and XRD. The presence of the amorphous component in the blend is found to influence the non-isothermal crystallization of HDPE. The addition of small quantities of SBR resulted in an increase in the rate of crystallization whereas nucleation is delayed. As compared to HDPE, larger crystallite size, a narrower size distribution, were observed in low SBR (~up to 30 wt%) content blends. The half time of crystallization also found to reduce as the SBR content in the blend increased. However, a lower degree of crystallinity was observed in these blends. The results thus show that incorporation of SBR in HDPE, while accelerating the rate of crystallization, lower the degree of crystallization. The reduction in the overall crystallization rate at high-SBR content is attributed to a decrease in the growth rate in the later stages of crystallization. It is observed that in dynamically cross-linked blends, the presence of crosslinked SBR that can acts as heterogeneous nuclei facilitated the nucleation of HDPE. However, the crystal growth may be impeded. As a result the overall crystallinity of the crosslinked blends found to decrease. From XRD profiles it had seen that addition of SBR and dynamic crosslinking does not exert an effect on the crystalline structure of HDPE. The dynamic vulcanization of SBR/HDPE blends enhanced the process of crystallization of HDPE phase. These conclusions are supported by the thermal characterization (DSC) results also.

Microstructure and fracture behavior of maleated high‐density polyethylene/ silicon carbide nanocomposites toughened with poly(styrene‐ethylene‐butylene‐styrene) triblock copolymer

AbstractMaleated high‐density polyethylene (mPE) consisting of 95 wt% high‐density polyethylene and 5 wt% polyethylene‐graft‐maleic anhydride was filled with 2–4 wt% silicon carbide nanoparticles (SiCp) and toughened with 10–30 wt% poly(styrene‐ethylene‐butylene‐styrene) (SEBS). Such mPE nanocomposites were compounded in a twin‐screw extruder followed by injection molding. The effects of SEBS elastomer and SiCp additions on the structure, thermal and mechanical behavior, and fracture toughness of mPE composites were studied using X‐ray diffraction (XRD), polarizing optical microscopy (POM), differential scanning calorimetry (DSC), heat deflection temperature (HDT), tensile test, Izod impact, and essential work of fracture (EWF) techniques. XRD and POM results showed that SEBS and SiCp additions reduce the crystallite thickness and spherulite size of mPE. DSC and HDT measurements revealed that SiCp addition promotes nucleation of HDPE crystals and markedly increases the range of elevated temperature over which mPE hybrids maintain adequate stiffness. Tensile test results showed that SEBS reduces the Young's modulus and yield strength of mPE, whereas SiCp stiffens and reinforces the mPE/SEBS blend. The Izod impact test was conducted at liquid nitrogen temperature. The impact strength of mPE/SEBS/SiCp hybrids improved dramatically with increasing SEBS content. EWF results obtained at room temperature showed that the specific EWF of mPE/SEBS blends and mPE/SEBS/SiCp hybrids also increases with increasing SEBS content. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 30: 322–333, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20228

Effect of whiskers nucleation ability and shearing function on the interfacial crystal morphology of polyethylene (PE)/raw whiskers composites

In this work, in order to investigate the combined effect of whiskers nucleation ability and shearing function on the interfacial crystal morphology of HDPE/raw whiskers composites, two different types of raw whiskers (SMCW and BW) with different diameter distribution and HDPE composites were firstly prepared by melt blending and then subjected to both traditional and dynamic injection molding. The results indicated that the nucleation ability of SMCW on HDPE crystallization is much better than BW. Furthermore, the small diameter whisker shows the better nucleation ability than the large diameter whisker. For samples prepared by traditional injection molding, the better the nucleation ability of the whisker, the more dense the HDPE crystal lamellae can epitaxially grow on its surface. However, after introducing shearing function, even for large diameter BW whisker with weak nucleation ability, a large number of HDPE crystal lamellae could be epitaxially grown on the surface of the whisker. As a consequence, the interfacial adhesion and mechanical properties of the composites are significantly improved by introducing shear function.

Effect of melt vibration on structure and mechanical properties of HDPE/nano-CaCO3 blend

Melt vibration technology was used to prepare injection sample of HDPE/nano-CaCO3 blend, whose mechanical properties were improved significantly. Compared with conventional injection molding, the enhancements of the tensile strength and impact strength of the sample molded by vibration injection molding were 41.2 and 43.2%, respectively. According to the SEM, WAXD, and DSC measurement, it was found that a much better dispersion of nano-CaCO3 in sample was achieved by vibration injection molding. Moreover, crystal orientation degree of matrix HDPE increased under the effect of melt vibration. The crystallinity degree of HDPE in vibration sample increased by 5.5% compared with conventional one. The improvement of mechanical properties of HDPE/nano-CaCO3 blend prepared by low-frequency vibration injection molding attributes to the even distribution of nano-CaCO3 particles and the orientation of HDPE crystals and increase of crystallinity degree under the influence of melt vibration.

Crystallization and final morphology of HDPE: Effect of the high energy ball milling and the presence of TiO2 nanoparticles

The influence of high energy ball milling process, HEBM, and the presence of TiO2 nanoparticles on the non-isothermal crystallization and fusion behavior of the HDPE were investigated. HEBM was used to homogeneously disperse TiO2 nanoparticles into a high density polyethylene, HDPE. Differential scanning calorimetry was used to analyze their non-isothermal crystallization and fusion behavior while, with X-ray diffraction the crystalline structures were determined. Atomic force microscopy was used to study the influence of the presence of nanoparticles on the final morphology of the polymer. It has been demonstrated that HEBM is a good method to prepare nanocomposites of well dispersed TiO2 nanoparticles within an HDPE matrix. When nanoparticles are absent the HEBM induces reduction of crystallinity of the polymer although a double crystallization process was observed; however, when nanoparticles are present, in addition of being favored the appearance of a metastable monoclinic phase, the fraction of crystals increases as milling time increases. AFM clearly showed how well dispersed were the TiO2 nanoparticles within the HDPE and how they are localized exactly between the lamellas. This result is the first clear visual evidence confirming that well dispersed nanoparticles actually do not act as nucleating agents in semicrystalline polymers. It was also shown that a 2% by weight of well dispersed TiO2 nanoparticles within the HDPE matrix induces a more homogeneous crystallization leading to denser spherulites with thicker lamellae.

Fractionated Crystallization of High-Density Polyethylene as an Evidence of Dispersed Phase Morphology in PET/HDPE Blends

The fractionated crystallization of HDPE as a dispersed phase in immiscible polymer blends with PET at composition of 15 wt-% was investigated. The dramatic influence of the molecular weight of the HDPE on its melt viscosity and therefore on the dispersion is reflected on the relative intensities of the twin peaks that are observed during the crystallization of the PE phase. The minimum volume of a nucleated domain was found to be in agreement with the typical size of PE spherulites. The effect of the addition of a compatibilizer of the E-GMA type was also studied.

Rice straw fiber-reinforced high-density polyethylene composite: Effect of fiber type and loading

Composite panels using virgin and recycled high-density polyethylene (VHDPE and RHDPE) and five types of natural fibers including four rice straw components (i.e., rice husk, rice straw leaf, rice straw stem, and whole rice straw) and wood fiber as control were made by melt compounding and compression molding. Fiber characteristics and the influences of fiber type and loading rate on HDPE crystallization behavior and composite mechanical properties were investigated. Fiber length and aspect ratio distributions for all fibers followed a lognormal distribution after milling with two parameters defining the curve location (i.e., mean fiber length/aspect ratio) and shape (i.e., mean fiber length/aspect ratio distribution). For both VHDPE and RHDPE, rice straw fiber systems had comparable mechanical properties with those of wood composites. Increase in fiber loading led to increased moduli and decreased tensile and impact strength. Composite panels with rice husk had the smallest storage moduli, but their impact strength was comparable or better than that of other straw fibers. Very little difference in mechanical properties existed among leaf, stem, and whole straw fibers. The particular recycled HDPE resin and its composites had significantly better moduli and strength properties compared to the virgin HDPE systems due to additives used during initial processing. X-ray diffraction experiments showed that introducing fiber to HDPE matrix did not change characteristic peak position, but the fiber increased crystalline thickness of HDPE system. Differential scanning calorimetry experiments showed that VHDPE had significantly larger peak heat flow during cooling run than the RHDPE, indicating higher crystallization rates for VHDPE. The use of fiber in both resin systems led to the reduced peak heat flow rate. The study showed that rice straw fibers can work well with both VHDPE and RHDPE as reinforcing filler. Future work will deal with effect of coupling treatments of the straw fibers in single phase or commingled plastics composite systems.