Crystallinity as a selection criterion for engineering properties of high density polyethylene

The Differential Scanning Calorimeter (DSC) was used to discriminate among 25 commercial high density polyethylenes (HDPE) on the basis of their degree of crystallinity and melting temperature. The area under the melting endotherm correlated directly with density and inversely with creep and thermal expansion measurements. Since high crystallinity was related to the design required properties of density, creep, and thermal expansion, DSC studies readily identified eight of the more promising polymers from the group of 25. The overall crystallization kinetics of polyethylenes with 75 percent crystallinity were analyzed by the Avrami and Fischer-Turnbull equations. Results indicate small disk-like spherulites (Avrami n = 2) following nucleation-controlled growth kinetics. These conclusions are in reasonable agreement with polarizing microscope observations. An equilibrium melting temperature between 141 and 142°C was estimated from Hoffman-Weeks plots. Processing thick parts from highly crystalline polyethylene is difficult because of the 14 percent volume change on crystallization. Higher degrees of crystallinity are associated with moderate molecular weight, so the viscosity range of these polyethylenes is not especially suited for processing by extrusion. These caveates necessitate tradeoffs between optimal design properties and processing requirements for HDPE parts.     

Thermo-mechanical properties of polyethylene composites filled with soapstone waste

In this study, soapstone waste originated from craftsmanship activities was used as an alternative filler (0–30 wt%) for a high-density polyethylene (PE) matrix. The aim of this paper is to understand the effect of the filler particles on crystallinity, thermal stability and thermo-mechanical properties of this newly developed composite material. Physico-chemical characterization was performed by x-ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. Thermogravimetric analysis (TGA), oxidation induction time (OIT) and dynamic mechanical thermal analysis (DMA) were performed to assess the effect of the filler on the themo-mechanical properties of PE. Thermal stability, measured by TGA, was enhanced, while OIT values reduced with filler content. A significant increase on the storage modulus of the composites (up to 148% in comparison with unfilled PE) was observed and this reinforcing effect was even more prominent at higher temperatures. XRD analysis revealed that the degree of crystallinity improved significantly with soapstone loading, which explains the substantial increase in stiffness observed. Increased crystallinity is also associated with higher strength, reduced residual stress, and better dimensional stability of end products, which can be particularly attractive for pressure pipe applications.     

Complex modification effect of linseed cake as an agricultural waste filler used in high density polyethylene composites

Linseed cake (LC) is a by-product of agricultural industry which does not have any large-scale industrial applications. The possibilities of its utilization as filler with plasticizing ability for high density polyethylene (HDPE)-based composites have been investigated. Composites containing 5, 10, 20 and 30 wt% of the waste filler have been prepared using a melt mixing method. The influence of the LC on the mechanical and thermomechanical properties of the composites, as well as their water absorption and morphology, have been evaluated by the following methods: static tensile test, impact strength assessment using Dynstat method, hardness measurements, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy observations, measurements of Vicat’s softening temperature and water uptake test. Application of different measuring techniques allows for describing complex modification effects of the composites’ properties changes induced by the presence of lignocellulosic filler with high oil content. The results of the study proved a pronounced influence of LC on high density polyethylene-based composites, especially a plasticizing effect of crude linseed oil contained by the waste filler particles. LC also has been assumed to affect the polymeric matrix crystallization process. It was found that complex modification of polyethylene results from simultaneously occurring different phenomena including: plasticization of the HDPE by linseed oil, improved crystallinity of the semicrystalline matrix, presence of the rigid lignocellulosic particles dispersed in polymer and accumulation of the oil in the interfacial regions.     

Barrier properties of polyamide-6/high density polyethylene blends

SUMMARY The barrier properties of Polyamide-6 (PA6)/High Density Polyethylene (HDPE) blends with and without compatibilizer prepared by ribbon extrusion were studied. The results show that the toluene diffusivity was improved by the addition of an interfacial agent and by inducing orientation of the polymer chains. The presence of PA-6 in the blend results in a decrease of the toluene diffusivity. This reduction is even larger for the case of the interfacial modified system. However, the most important reduction of the toluene diffusivity is observed for pure HDPE when stretched. A six-fold decrease is observed when the draw ratio is increased two fold. In the case of the permeability of different solvents through blends a gravimetric permeation cell was used. The results show that the permeability decreases with increasing size of the penetrant molecules (CH₂Cl₂, CHCl₃ and CCl₄) and this decrease is more important for a compatibilized blend. Received: 1 December 2000/Revised version: 21 March 2001/Accepted: 21 March 2001     

Crystallization of low‐density polyethylene embedded inside zinc oxide nanoparticle percolating network

The crystallization behavior of low‐density polyethylene (LDPE) embedded inside zinc oxide (ZnO) percolating network (LDPE/60 vol% ZnO) was investigated via differential scanning calorimetry (DSC), and compared with those of LDPE bulks (neat LDPE and LDPE/1.15 vol% ZnO). Results revealed that embedded LDPE possessed by far shorter half‐crystallization time at elevated crystallization temperatures than LDPE bulks, whereas at lower crystallization temperatures longer half‐crystallization time was observed. Isothermal crystallization kinetics study revealed that the Avrami exponent of embedded LDPE varied in range of 1.8–2.0, indicating quasi‐two‐dimensional crystallization with heterogeneous nucleation, contrasting with about 3 for LDPE bulks. Moreover, crystallization activation energy of embedded LDPE was much larger than that of neat LDPE due to geometric confinement effect of ZnO network. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Ageing of polyethylene filled with a mineral filler

The thermo-oxidation resistance and weatherability of LDPE and HDPE compositions, containing up to 45 wt.% calcium carbonate, are investigated. The thermo-oxidation resistance is investigated by dynamic DTA and natural ageing is carried out in an exposure station in a seaside climate. The change in strength and colour after ageing is determined. The behaviours of filled and unfilled polymers are compared. Empirical equations are given, describing the change in the investigated parameters during natural ageing.     

Utilization of renewable filler from lichen in low density polyethylene

New organic filler, obtained from a local lichen type, Rinodina Poeltii, was utilized in low density polyethylene (LDPE). Thermal characterization of organic filler revealed its suitability to be used as filler during extrusion and injection processes. Filler did not exhibit any weight loss up to 300°C except the dehydration loss at 155°C. Unmodified filler was compounded as 5, 10, and 15% by weight with LDPE. Filler addition resulted in a decrease for both tensile strength and % elongation at break. However, an increase was observed in elastic modulus. The compatibility of the filler material and polymer matrix was also found to be good as a result of absence of pull out voids in SEM observation. POLYM. COMPOS., 38:389–395, 2017. © 2015 Society of Plastics Engineers     

Effects of conductive graphite filler loading on physical properties of high‐density polyethylene composite

High‐density polyethylene (HDPE)/graphite nanocomposites containing up to 30 vol% of graphite powder filler were prepared by melt mixing in a Brabender Plasticorder at 180°C for 15 min. The nanocomposites were characterized for their rheological, dynamic mechanical, crystallographic, and electrical properties as a function of graphite loading. The results indicated that graphite loading affects storage modulus, loss modulus, complex viscosity, and conductivity of HDPE matrix. The storage modulus increases while the graphite loading increases in the studied concentration range (up to 30%). When the graphite loading was increased to 30%, storage modulus at room temperature was about 300% higher than that of pure HDPE. Also, the composites containing 20 and 30% graphite shows more conductivity than the others. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

振动挤出HDPE管材的结构与力学性能

使用自制的电磁动态塑化挤出机和螺旋芯棒式机头挤出高密度聚乙烯(HDPE)管材.采用爆破压力测试,拉伸性能测试,差示扫描量热法分析等研究振动频率和振幅对HDPE管材结构与力学性能的影响.振动挤出的HDPE管材周向强度显著提高,实现了管材的双向自增强.与稳态相比,振动挤出的HDPE管材结晶度提高,熔点升高,结晶完善;爆破压力最大提高了34.2%,轴向拉伸屈服应力最大提高了5.3%.     

Decorated wood fiber/high density polyethylene composites with thermoplastic film as adhesives

It is difficult for wood fibers/high density polyethylene (WF/HDPE) composites to laminate with poplar (Populus tomentosa) wood veneer due to its nonpolar and imporous surface. In present study, four types of thermoplastic films, include two sorts of chlorinated polypropylene (CPP32 and CPP22) film and a mixture film of maleic anhydride grafted polyethylene (MAPE) and HDPE, were developed to glue poplar wood veneer onto WF/HDPE composite board under heat-pressing. The intermediate layer has well water resistance when used aforementioned films. Optical microscopy and scanning electron microscopy (SEM) results show that CPP32 with higher melt flow rate had the higher permeability into poplar wood and fitness with WF/HDPE surface than CPP22; accordingly, the bonding strength of CPP32 was higher than CPP22. MAPE/HDPE film formed the strongest bonding layer for the high compatibility with the WF/HDPE surface which confirmed using SEM, and the covalent bonding between the poplar veneer and MAPE were confirmed using fourier transform infrared (FTIR). Compared to the high heat-press temperature of MAPE/HDPE, CPP32 has the lower processing temperature and acceptable bonding strength. CPP32 and MAPE/HDPE film both suited as the bonding intermediary to substitute traditional adhesive to manufacture veneered wood-plastic composite boards.     

过氧化物交联HDPE材料的研究

研究了交联用高密度聚乙烯(HDPE)的种类、交联剂二叔丁基过氧化物(DTBP)、助交联剂T的用量对交联HDPE复合材料结构和性能的影响。选用辛烯为共聚单体和支化度(每1000C中的甲基数)为3.2的HDPE为原料树脂,主交联剂DTBP和助交联剂T的质量分数分别为0.15%,0.20%时,材料的各项性能符合交联HDPE管材的要求。     

反相气相色谱法表征HDPE的表面性质

采用反相气相色谱技术,分别测定不同分子探针在不同温度下通过高密度聚乙烯(H DPE)的保留时间,计算HDPE表面色散自由能与表面Lewis酸碱常数.HDPE表面色散自由能随温度的升高呈线性降低,且为弱碱性的Lewis两性聚合物材料.     

Impact yielding of high density polyethylene

We have used a projectile impact method to estimate the flow stress of high density polyethylene at a strain rate of 3 × 10³ sec⁻¹. The technique was developed initially by Taylor and applied successfully by Whiffin and others to ductile metals. The data from this experiment have been compared with data obtained in more conventional compression and drop hammer tests at lower strain rates at 20° and 100°C. The flow stress of high density polyethylene deduced from the impact test at 20°C is significantly higher than that anticipated from a simple extrapolation of the low strain rate data at 20°C. The data at 100°C are however in good agreement. The technique has also been used to estimate the flow stress of high density polyethylene as a function of temperature over the range −20° to +105°C. These data indicate that the discrepancy in the data for 20°C arises from a real discontinuity in the response of the polymer rather than from an inadequacy in the theoretical analysis of the impact experiment as applied to polymeric solids. We conclude that the impact method described is a useful technique for estimating the flow stress of polymers. It is however limited to a relatively narrow range of strain rates.     

加工助剂对HDPE流变性能的影响

采用熔体流动速率仪、毛细管流变仪和Haake流变仪研究了极性低聚物、含氟聚合物、有机硅化合物3种加工助剂对高密度聚乙烯(HDPE)流变性能的影响,并对其作用机理进行了探讨。研究发现:熔体流动速率仪和毛细管流变仪无法表征这三种加工助剂对HDPE的降黏作用;用Haake流变仪测试表明,加入1 000μg/g加工助剂就能明显降低HDPE在挤出过程中的加工扭矩,进而降低能耗,提高机器寿命和生产效率;极性低聚物和有机硅化合物降低HDPE扭矩的机理和含氟聚合物不同,是内外润滑作用相结合的复合效果。     

Thermal characteristics of surface-crosslinked high density polyethylene beads as a thermal energy storage material

High density polyethylene (HDPE) beads were surface-crosslinked in a modified plasma reactor by using argon plasma. The modified plasma reactor can treat a large amount of beads to be uniformly surface-crosslinked. The objectives of this study were to develop a shape-stabilized functional thermal energy storage material and to find an optimum plasma reaction condition out of various operations. To achieve these objectives, we systematically studied the effects of the gas pressure, the radio frequency (RF) power and the treatment time on the degree of crosslinking. The degree of crosslinking was measured by solvent extraction method (BXM: boiling xylene method). The chemical and physical characterization of the material was performed by using fourier transform infra-red (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Finally, we confirmed the thermal stability of surface-crosslinked HDPE through about 50 thermal cycling tests.     

高密度聚乙烯/硅橡胶热塑性硫化胶的制备与性能

采用动态硫化法制备了高密度聚乙烯（HDPE）/硅橡胶（MVQ）热塑性硫化胶（TPV）,考察了HDPE与MVQ的质量比及压片工艺对TPV的硫化特性、力学性能及表面亲疏水性能的影响。结果表明,随着MVQ用量的增加,TPV的动态硫化程度逐渐升高。随着压片时间的延长,TPV的拉伸强度、撕裂强度和扯断伸长率均大幅提高。随着MVQ用量的增加,TPV与水的接触角逐渐增加,相应的表面张力逐渐减小。     

高密度聚乙烯/丁苯橡胶热塑性硫化胶的形状记忆性能

采用动态硫化法制备了高密度聚乙烯(HDPE)/丁苯橡胶(SBR)热塑性硫化胶(TPV),研究了橡塑比、定型温度、回复温度及增容剂苯乙烯-丁二烯-苯乙烯嵌段共聚物(SBS)对HDPE/SBR TPV形状记忆性能的影响,观察了其微观结构,提出了形状记忆行为机制。结果表明,HDPE/SBR TPV具有典型的海-岛结构,拉伸后其表面存在明显的取向结构;SBS能显著提高HDPE/SBR TPV的形状记忆性能,当SBS用量为6份、定型温度和回复温度均为120℃时,HDPE/SBR TPV的形状记忆性能最佳。     

Dynamic mechanical properties of high density polyethylene and teak wood flour composites

The dynamic mechanical properties of high density polyethylene (HDPE) and teak wood flour (TWF) composites at varying volume fraction (Φ _f) of TWF from 0.00 to 0.32 have been studied. In HDPE/TWF composites, storage modulus (E′) decreased at Φ _f = 0.05, then increases with Φ _f; however, values were lower than HDPE up to Φ _f = 0.16, due to a pseudolubricating effect of filler. Loss modulus (E″) values were higher than HDPE in β and α relaxation regions while in γ relaxation region values were marginally equal to HDPE. Tan δ value decreases with Φ _f which may be due to enhanced amorphization and decreased crystallinity of HDPE. In presence of maleic anhydride grafted HDPE (HDPE-g-MAH), E′ values were lower than HDPE/TWF composites. In HDPE/TWF/HDPE-g-MAH, E″ were slightly higher than HDPE/TWF due to slippage of HDPE chains facilitated by the extent of degradation of coupling agent. Tan δ were higher for both systems than the rule of mixture.     

Thermal conductivity of high density polyethylene filled with graphite

The effect of the grade, the content, and the particle diameter on the thermal conductivity of high‐density polyethylene (HDPE) filled with graphite were studied. The results show an increase of thermal conductivity of the HDPE/graphite composite with increase of graphite content. The thermal conductivity of the HDPE filled with the expanded graphite was larger than that of the HDPE filled with the colloid graphite system. At the same volume content (7%), the thermal conductivity of the former was twice that of the latter one. The particle diameter of the graphite also affected the thermal conductivity of HDPE composites. With increase of the particle diameter of the colloid graphite, the thermal conductivity of the HDPE/graphite increased. However, when the particle diameter of colloid graphite was larger than 15 μm, the increase of thermal conductivity of HDPE/graphite changed by inches. Some models proposed to predict thermal conductivity of a composite in a two‐phase system could not be applied to HDPE filled graphite powder composites, such as Maxwell‐Eucken, Cheng and Vachon, Zieblend, Lewis and Nielsen, Agari and Uno equations. But, according to the increase of thermal conductivity of HDPE composites filled with the colloid graphite, we find that Ziebland equation is suitable except of some constant. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3806–3810, 2006     

Flammability and thermal properties of high density polyethylene/paraffin hybrid as a form‐stable phase change material

In this study, form‐stable phase change material (PCM)–high density polyethylene (HDPE)/paraffin hybrid with different flame‐retardant systems are prepared by using twin‐screw extruder technique. This kind of form‐stable PCM is made up of paraffin (a dispersed phase change material) and a HDPE (a supporting material). Their structures and flammability properties are characterized by scanning electronic microscope (SEM) and cone calorimetry. Thermal stability is shown by thermogravimetry analysis (TGA) and its latent heat is given by differential scanning calorimeter (DSC) method. SEM results show that the HDPE forms a three‐dimensional net structure and the paraffin is dispersed in it. The peak of heat release rate (HRR) of the flame‐retardant form‐stable PCM decreases markedly. In TGA curves, although the onset of weight loss of flame‐retardant form‐stable PCMs occur at a lower temperature than that of form‐stable PCM, flame‐retardant form‐stable PCMs produce a large amount of char residue at 700°C. DSC results show that the addition of flame retardant has little effect on the phase change latent heat of PCM. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1320–1327, 2006