Structure–property correlations of flexible clear coats

In this paper thermomechanical and mechanical properties of various free clear coat films for coil-coated steel sheets were studied by dynamic mechanical analysis and tensile testing. To establish structure–property correlations, polyacrylate and polyester binder resins with varying molar mass and functionality were investigated. The clear coat films based on polyacrylate binders exhibited higher glass transitions values, crosslinking densities, elastic modulus and tensile strength values. For both resin types, a relationship of the properties glass transition temperature, crosslinking density, stiffness and tensile strength and the functionality considering the molar mass and the hydroxyl value of the resins was obtained. The elastic strain energy of the investigated brittle clear coat films depended mainly on the elastic modulus.     

Preparation and characterization of modified starch‐based plastic film reinforced with short pulp fiber. II. Mechanical properties

Native corn starch‐ and hydroxypropylated starch (HPS‐) based plastic films were prepared using the short pulp fiber as the reinforcement and the glycerol as the plasticizer. The results of tensile test showed that the strain and stress at break and elastic modulus increased with pulp content. With glycerol content, the strain at break increased considerably, but the breaking stress and elastic modulus decreased. And the stress–strain curves showed that the brittleness problem of films was overcome by the pulp, glycerol, and water content. The hydroxypropyl starch films showed results similar to those of the native starch films. The results of the three‐point bending test showed that maximum deflection, flexural strength, and specific work increased with pulp content, but the flexural modulus was the highest at a pulp content of 20%. And with the glycerol content, the maximum deflection and specific work of rupture increased, but the bending elastic modulus decreased. The hydroxypropyl starch films showed results similar to those of native starch films as far as the maximum deflection and flexural strength were concerned, but the bending elastic modulus and specific work of the hydroxypropyl starch films were considerably lower than those of starch films. So it was concluded that the flexibility of films was improved by the hydroxypropylation. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2108–2117, 2003     

Synthesis and characterization of silicone-modified polyester as a clearcoat for automotive pre-coated metals

Four types of silicone-modified polyester resins were synthesized for cleanable characteristics with silicone intermediate, which has a long chain, to extend the polymer chains of the resins. These resins were formulated to make polyester/melamine heat-cured coatings to control the formability. The characteristics, viscoelastic behavior and flexibility of the resins were measured by DMA and tensile test. The contact angle measurement can be measured by the water repellence of the coating surface, which is a standard method to evaluate cleanable characteristics. The surface free energy was calculated by the contact angle measurement, and the surface analysis of each cured coating was evaluated using an XPS. Silicone-modified polyester coatings were coated on the cold rolled steel sheets to verify their formability, using a deep drawing test. Results showed that the storage modulus decreased, and the glass transition temperature shifted to a lower temperature with increasing contents of silicone intermediate. So, silicone intermediate provides lower stiffness and higher softness to polyester coating. To analyze the formability, we calculated F_U (the forming coefficient based on strain energy) and F_? (the forming coefficient based on strain). When F_U and F_? are both larger than 1, the polyester coatings have good formability. CSiPE-3 and CSiPE-5 had good formability. Also, CSiPE-5, which had the highest amount of silicone intermediate, had 93.5° of water contact angle, and had 26.5 mN/m of surface free energy and had 5.5 N/25 mm of the peel strength. So, it is implied that silicone intermediate can give a low surface energy and peel strength to polyester coatings. From those tests, the polyester/melamine coating of CSiPE-5 that had 0.5 mol of silicone intermediate had good formability and low peel strength, which are semi-removable characteristics. So, it would be an appropriate coating as a clearcoat for automotive pre-coated metals.     

Effect of the extensional flow on the properties of oriented nanocomposite films for twist wrapping

In this study, we examined the mechanical behavior of nanocomposite films based on polyethylene (PE) and pristine PE films. The films were prepared by film blowing and were then cold‐drawn at low temperature. The experimental results show that cold drawing significantly enhanced the orientation; with increasing draw ratio (DR), the elastic modulus and tensile strength of the PE films strongly increased, particularly in the presence of the organoclay. To obtain polymeric films suitable for twist wrapping, the films must be sufficiently stiff so that no shrinkage or elastic recovery occur during or after twisting. The elongation at break and the yield strain sharply decreased with orientation, mainly in films upon drawing. According to the mechanical behavior, the twist angle increased with increasing DR and, particularly, with the addition of nanoclay, probably because of the applied DR, which reduced the nanoparticle size and, as a consequence, hindered the applied torsional elastic recovery. Therefore, the nanocomposite film with a higher DR was particularly suitable for twist‐wrapping applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Experimental study on cold press workability of aluminum-polyethylene sandwich laminates

The cold press workability of aluminum-polyethylene sandwich laminates is experimentally investigated by a deep drawing process with a conical die. “Planium” of 2 mm thickness, in which the core layer, high density polyethylene, is sandwich-laminated between two aluminum sheets, is used as a test specimen. Soybean oil is employed as a lubricant. The dimensions of the drawing die set are determined for a circular, blank so that the tensile fracture of the drawn.cup occurs at the top corner of the punch. The limiting draw ratio (LDR) is experimentally explored by using many blanks of various initial diameters. In general the maximum punch load in successful drawing increases linearly with increasing draw ratio. Because of the sandwich structure, the fracture of the drawn cup occurs twice. The initial fracture (LDR_s) corresponds to a fine bending fracture at the aluminum surface. The second fracture (LDR_B) is the complete fracture of the whole laminate. The effect of punch corner radius, working velocity and thickness fraction of aluminum and polyethylene on LDR_S and LDR_B are studied. The strain distributions of deep drawn cup in three orthogonal directions are analyzed experimentally.     

Mechanism of interfacial bond failure

The mechanism of interfacial bond failure is discussed with reference to the maximum shearing strain energy theory for a steel/nylon 12/steel cross-lap joint and an aluminium/nylon 12 laminate. The tensile bond strength is found to increase with the degree of crystallinity of the adhesive, owing to its higher yield strength. The 180°-peel strength increases with the decrease in the crystallinity, due to its higher deformability. Interfacial bond failure occurs when the adhesive near the interface yields, under conditions such that the shearing strain energy reaches the value equivalent to the yielding point of the adhesive.     

Synthesis and characterization of acrylic-grafted polyester coatings for automotive pre-coated metal

An automotive pre-coated metal (PCM) system has been investigated to remove the wet coating process, such as pre-treatment, dip coating and spray coating for environmental regulations. However, automotive pre-coated metal sheets must have high flexibility and stiffness to overcome the harsh conditions such as encountered in cutting, press and the stamping process. For these reasons, a series of acrylic-grafted polyester coatings (i.e., AGP-0, AGP-10, AGP-20, AGP-30) were designed to satisfy both the surface hardness and the formability for an automotive PCM. The characteristics of the resins were measured by GPC, FT-IR and ¹H NMR. The viscoelastic behavior and flexibility was evaluated using DMA and UTM. The physical properties such as pendulum hardness, pencil hardness and adhesion were measured to define the effect of incorporating acrylates. A cylindrical deep drawing tester was used to evaluate the formability of coatings.     

Mechanical nondiscoloring and antistretching photonic crystal films based on Zn2+ coordination and hydroxypropyl methylcellulose

Mechanical nondiscoloring and antistretching photonic crystal (PC) films, especially those with stable structure colors during deformation, have great potential applications in wearable display devices, decoration, and packaging. Here, PC films with antistretching and invariant structural colors during deformation were prepared, by combining Zn²⁺ coordinated elastic material and hydroxypropyl methylcellulose (HPMC) with polystyrene@silica (PS@SiO₂) colloidal crystals. The PC films release energy by forming local fractures at a microscopic level during the straining process but the lattice spacing and effective refractive index of the local array do not change. According to the Bragg law, the structure color remains unchanged. The introduction of HPMC gave the PC films excellent tensile properties, and the maximum tensile strength reached 10 MPa. And after 100 times of stretching, bending and compression cycles, the structural color remained unchanged.     

Mechanical properties of ultrahigh-molecular-weight polyethylene fiber-reinforced PE composites

Three types of high-strength polyethylene (PE) fiber-reinforced composite sheets were made by compression molding at the vicinity of melting point of the fiber. Sheet I was molded from only PE fibers. Sheets II and III were prepared by the compression molding of PE fiber with conventional high- and low-density polyethylene films, respectively. The mechanical properties, thermal behavior, and morphologies of the sheets have been investigated and compared with each other. The tensile strength and elastic modulus of sheet III are 660 MPa and 14 GPa, respectively, which were 60 and 30 times higher than those of typical low-density PE film. Although the elastic modulus of sheet III is 6 GPa less than that of sheet II, the tensile strength of 660 MPa is highest in the three types of sheets prepared in this study. The mechanical properties of sheets II and III were about half of predicted theoretical ones. It was concluded that the interfacial adhesion between PE fiber and PE matrix was an important factor to improve the mechanical properties of this PE sheet. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1431–1439, 1998     

微细钢纤维对高弹性模量混凝土力学性能的影响

基于修正的Furnas堆积模型和骨料紧密堆积试验设计了一种高弹性模量混凝土,并利用微细钢纤维改善高弹性模量混凝土的韧性,研究了钢纤维体积掺量对骨料紧密堆积状态下混凝土流动性能、强度、弹性模量及弯曲韧性的影响规律。结果表明:采用紧密堆积骨料和适量微细钢纤维可以构筑高弹性模量韧性混凝土,其静弹性模量和动弹性模量最高分别可达50.15 GPa和53.23 GPa,断裂能可达5 680.45 N/m,残余弯曲韧度比从0增加到0.43;高弹性模量混凝土的流动性能随着钢纤维掺量的增加而降低,抗折强度、弹性模量及弯曲韧性则均随着钢纤维掺量的增加而增加,混凝土的抗压强度随着钢纤维掺量增加先增加后降低。在骨料紧密堆积状态下,综合考虑流动性能、力学性能和工程经济性,高弹性模量混凝土中微细钢纤维的合理掺量为0.4%(体积分数)。     

不同加固方式对钢筋混凝土梁抗弯性能的影响

以我国某条高速公路的改扩建工程中的预应力钢筋混凝土梁为原型,通过缩尺模型,设计了3根试验梁,主要研究了CFRP布加固法和预应力钢绞线加固法对桥梁结构弯曲性能的影响,分析了试验梁极限承载力的变化,梁体的挠度,混凝土、钢筋及加固材料的应变,裂缝数量及发展情况等.试验结果显示:CFRP布加固法和预应力钢绞线加固法均能有效提高梁体的承载能力;CFRP布加固法通过分散受拉区混凝土所受的拉应力,限制混凝土裂缝的发展;预应力钢绞线加固法约束梁体弯曲变形的效果非常明显,可以有效减小梁体的挠度.     

Effect of uniaxial drawing of soy protein isolate biopolymer film on structure and mechanical properties

The effect of uniaxial drawing of biodegradable soy protein isolate (SPI) polymer film on mechanical properties was investigated to accelerate the efforts to develop SPI films with improved properties. The films containing 0–30 wt% glycerol were drawn uniaxially up to a draw ratio of 2.5. The mechanical properties of the SPI film increased significantly after uniaxial drawing. The tensile strength of the undrawn film (49.7 MPa) was approximately doubled by subjecting the film to uniaxial drawing to a D.R. of 2.5. Wide‐angle X‐ray diffraction and differential scanning calorimetry measurements did not show evidence of generation of a crystal phase in the drawn SPI films. ATR‐FTIR revealed that the protein film contained mainly α‐helix and β‐sheets secondary structures. Microwave molecular orientation analysis showed that birefringence increased with increasing draw ratios. Mechanical anisotropy of the SPI film via orientation of α‐helix and β‐sheets structure is thought to be responsible for the enhancement of mechanical properties with uniaxial drawing of the SPI films. POLYM. ENG. SCI., 47:374–380, 2007. © 2007 Society of Plastics Engineers.     

Ultra-high modulus isotactic polypropylene. I. The influence of orientation drawing and initial morphology on the structure and properties of oriented samples

The influence of a number of factors (temperature–speed regime and the quantity of draw stages, molecular weight of a polymer, etc.) on the deformability of initial isotropic IPP and on mechanical characteristics of highly-oriented samples, obtained in the process of a two-stages isothermal orientation drawing, was studied. It was shown that the maximum achievable values of elastic modulus and draw ratio depended not only on the molecular weight of a polymer and the sizes of spherulites, constituting initial IPP, but on the structural organization of inner-and interspherulite regions. Upon physical aging of initial isotropic films, irreversible structural changes take place, which result in the formation of microvoids while being drawn and in the reduction of mechanical properties of obtained material. An extremal dependence of elastic modulus and draw ratio of maximum drawn IPP samples on draw speed was discovered. A structural model, which is supposed to possesstie molecules with various degrees of tautness in amorphous layers, was proposed. Higher effectiveness of two-stage drawing in comparison with one-stage drawing was established. The optimum temperature–speed regime of orientation drawing, which permits the reception of highly oriented, ultra-high modulus IPP with maximum high mechanical characteristics (elastic modulus ～ 30–35 GPa and tensile strength ～ 1,1 GPa), was determined.     

Fabrication of High-Strength Biodegradable Composite Films of Poly (Vinyl Alcohol) and Fly Ash Crosslinked with Glutaraldehyde

A biodegradable composite film of poly (vinyl alcohol) reinforced with fly ash and glutaraldehyde was fabricated using a suspension of these materials in deionized water. The tensile strength and modulus of the films were found to increase proportionally with FA up to 20 wt%, and achieved the maximum 49% and 123% higher, respectively, than that of PVA. The percentage of strain at failure decreased exponentially with FA. The physical and/or chemical bonding in the systems (PVA, FA, and GLA) were directly characterized by the shift of stretching and bending peaks of the structure in the components with FTIR spectra.     

Characterization of clearcoats containing phosphoric acid-functionalized acrylic polyols for automotive precoated metal sheet coatings

In this study, the various physical and mechanical properties of clearcoats prepared through a new crosslinking method were investigated. The method was aimed at developing clearcoat systems to improve the deep-draw processing and formability performance in precoated metal (PCM) sheets for automotive applications. From phosphoric acid-functionalized acrylic polyols (PAFAPs) first synthesized in this study and glycidyl methacrylate-modified acrylic copolymer (GMAMAC), phosphoric acid-GMA modified acrylic polyols (PAGMAPs) were newly prepared as new binders in automotive clearcoats. Several clearcoats were formulated with different molecular weights and hydroxyl contents from PAFAPs and GMAMAC. Using clearcoats themselves, the crosslinking reactions for these clearcoats were compared by evaluating the curing behaviors with a rigid-body pendulum test (RPT) and the changes of chemical structures via attenuated total reflectance FTIR spectroscopy. The mechanical properties of the clearcoats were systematically characterized, using dynamic mechanical analysis (DMA) and universal testing machine analysis (UTM). Also, various tests were carried out using PCM sheets by depositing clearcoats above the same PCM-based primers and basecoat layers on galvanized steel. The fracture and deformation patterns related to surface damages on the clearcoat surface were visualized using a nano-scratch test, in association with atomic force microscopy. In particular, deep-draw processing tests, based on forming process simulations, were employed to scrutinize the effect of clearcoats developed in this study on the forming feature in PCM sheets. From the results of RPT, DMA, and UTM tests, the primary crosslinking networks of PAGMAPs from the synthesized PAFAPs and GMAMAC, and also succeeding secondary crosslinking networks between PAGMAPs and blocked isocyanates, were closely correlated with the degree of crosslinking (X _c), in accordance with the molecular weight between crosslinks (M _c), and glass transition temperature (T _g). As a result, the presented clearcoats with a long pendulum period, a low rubbery modulus, and a large tensile strain value, which are the significant factors for developing automotive PCM sheet technology, have truly demonstrated more superior formability during the deep-draw process. It is confirmed that properties of clearcoats with toughness and flexibility could be optimally controlled by PAGMAPs for automotive coatings.     

Biaxial orientation behavior of polystyrene: Orientation and properties

Square sheets of extrusion grade polystyrene (PS) were biaxially stretched using a laboratory biaxial stretcher. The effects of process parameters such as stretch ratio, drawing sequence, drawing speed, and temperature were studied. Birefringence, mechanical properties, and thermal shrinkage of the stretched sheets were the focus of this study. A high orientation was achieved at high stretch ratio, and orientations from uniaxial to equi‐biaxial were obtained by controlling the relative magnitude of stretch ratio in machine (MD) and transverse (TD) directions. Stretching increased tensile strength and elongation at break significantly, which indicated an improvement in the toughness of the oriented PS sheets. Those properties were correlated with biaxial orientation factors: a rapid increase was observed for both tensile strength and elongation at break for birefringence levels above ?0.005, and below, a plateau was observed. The shrinkage strain and stress were found to correlate well with the biaxial orientation factors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 487–496, 2003     

Experimental evaluation of reinforcing the single lap joint in both longitudinal and transverse direction under tensile and bending condition

The effect of pins and wires as reinforcing elements in the single adhesive joints under tension and bending has been investigated in this study. Four types of joint specimens were made for this reason. Type one specimen, having no reinforcements and type two having 20 metallic wires of 0.2 mm diameter in longitudinal direction. Type three consist of 6 steel pins having 1 mm diameter in transverse direction. In type four, both the pins in transverse and wires in longitudinal direction have been used to reinforce the joint. After manufacturing of the samples, their tensile and bending properties were investigated. The results show that, pins increase bending strength and toughness during both tensile and bending while metallic wires increase tensile strength and modulus of joint. Overall, the sample with combined reinforcements has the highest tensile and bending properties apart from modulus. Since the weight of the reinforcements used are negligible, the specific properties of the joint has been improved significantly. The tensile specific strength and toughness of combined reinforced joint as compared to simple joint with no reinforcement has been improved by 33.48% and 82.52% respectively. Also in that case, the specific bending strength and toughness are improved by 64.4% and 231.91% respectively.     

弯曲荷载下喷射混凝土衬砌碳化耐久性研究

以一般大气环境长大喷射混凝土单层永久衬砌隧道为背景,开展弯曲荷载作用下喷射混凝土衬砌碳化耐久性试验.采用改进的四点弯曲法,对应力比为0、0.25、0.50和0.75的混凝土试件进行快速碳化试验,并对无荷载混凝土试件的抗压强度、劈裂抗拉强度及抗折强度进行测试.以张誉碳化模型为基础,对其碳化系数进行修正,建立考虑应力比、受力方式、钢纤维和成型方式的喷射混凝土碳化深度预测模型.结果表明:喷射混凝土碳化深度符合Fick第一定律,碳化系数与受力方式和应力比、钢纤维及成型方式有关.喷射混凝土碳化耐久性优于模筑混凝土,钢纤维可进一步提升喷射混凝土碳化耐久性.碳化混凝土相对抗压强度和相对劈裂抗拉强度随碳化深度增大而增大,相对劈裂抗拉强度与碳化深度呈指数关系.通过将模型预测值与试验值进行对比,其平均偏差小于10%,标准差为0.07,对弯曲荷载喷射混凝土碳化深度的预测具有较好的适用性.     

玻纤增强PP热塑性片材的制备及力学性能研究

采用熔融浸渍法制备了玻璃纤维毡增强聚丙烯（PP）热塑性复合片材；通过在PP中加入复合改性PP改善了基体与增强纤维间的相容性；考察了相容剂、PP种类及玻纤毡种类对复合片材的影响。结果表明，相容剂的加入可使复合片材的拉伸强度提高29％、拉伸模量提高23％、弯曲强度提高42％、弯曲模量提高25％；高熔体质量流动速率PP可使片材的弯曲与冲击性能进一步改善。连续玻纤毡和长玻纤毡增强PP复合片材，前者综合力学性能良好，而后者则冲击强度较弱、弯曲性能加强。     

Characterisation of mechanical properties of thin polymer films using a bi-axial tension based on blow-up test

Abstract

Blow-up tests were carried out to evaluate mechanical properties of the thin Nylon film used as bagging films. A new method for calculating bi-axial stress and strain of the thin film in blow-up tests was developed based on the theory of membrane with large strain solutions. The bi-axial tensile elastic modulus, Poisson's ratio, yield strength, fracture stress and bi-axial stress–strain relationship of the thin Nylon film were obtained. Meanwhile, uni-axial tensile tests were conducted and the results were compared with those from blow-up tests. For the Richmond HS-8171 thin Nylon film studied, the bi-axial tensile elastic modulus was slightly more than 2 times greater than the uni-axial tensile elastic modulus. The yield strength was the same for both bi-axial and uni-axial tension. The bi-axial fracture stress was about one-third greater than the uni-axial one, while the bi-axial failure strain was about two-thirds greater than the uni-axial counterpart.