快速成型与耐热、高强度酚醛注塑料的制备技术及性能研究
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摘要
酚醛注塑料具有制品成型快,产量高,质量优异等优点,近年来受到了越来越多的关注,其中快速成型酚醛注塑料和耐热、高强度酚醛注塑料是其两个主要发展方向,另外对酚醛注塑料制品进行后固化处理可以强化其使用性能。本文主要对快速成型酚醛注塑料,耐热、高强度酚醛注塑料和酚醛注塑料制品后固化中的基础理论和工程技术方面的若干问题进行了系统的研究。
酚醛注塑料的成型性能主要涉及固化性能和流动行为两个方面,制备快速成型酚醛注塑料的技术关键在于合理解决快速固化与流动特性之间的矛盾。论文通过调控酚醛树脂结构,研究树脂的固化行为及其注塑料制备与成型过程中的化学流变特性,优化了制备工艺,有效地平衡了注塑料的固化成型性与流动特性间的关系。
首先考察了酚醛缩合反应体系中pH值、催化剂及物料配比等因素对酚醛树脂结构的影响,探索了高邻位酚醛树脂合成过程中影响反应稳定性的关键因素。研究表明,采用复合催化剂可以调控树脂的结构,得到不同O/P值(酚醛树脂链结构中的邻对位比)的酚醛树脂;控制反应后期羟甲基的浓度,可以抑制支化反应,使反应稳定地进行;用~(13)C-NMR方法可定量地表征酚醛树脂的结构及其O/P值。
酚醛树脂的固化行为直接影响到其注塑料的成型与注塑制品的性能。本文分别采用DSC分析和抽提等方法研究了不同O/P值酚醛树脂的固化活化能及固化历程。发现酚醛树脂的固化活化能随着其O/P值的增加而降低,固化进程变得更加容易。在酚醛树脂的固化过程中,先形成大量微凝胶,形成微凝胶的速度随树脂O/P值的增加而加快;微凝胶继续相互碰撞挤压进一步形成固化网络结构,该过程为扩散控制,固化速度不受酚醛树脂O/P值的影响。提高固化温度或树脂的O/P值可有利于固化结构与组成的均一性。
为了调控快速成型酚醛注塑料的固化程度及平衡注塑料的成型与流动性之间的关系,考察了辊炼工艺、树脂O/P值对酚醛注塑料的成型时间及流动特性的影响。发现树脂O/P值愈高,其注塑料的流动性随辊压温度或辊压时间的增加而
Phenolic resins and phenolic injection molding materials belong to an important group of thermosetting polymers with very good fire resistance, dimensional stability, and excellent insulation properties. However, some key issues, such as structure and curing of phenolic resins and chemorheology of phenolic injection molding materials, and viscoelastic and postcured characteristics of phenolics still remain to be resolved. In this work, phenolic injection molding materials with fast-curing characteristics, phenolic injection molding materials with high mechanical and heat resistance properties, and the postcured properties of different phenolic resin materials reinforced with wood flour and glass fiber also investigated systematically.Injection properties of phenolic injection molding materials are related to curing and flowability. The key technical point in preparing phenolic injection molding materials with fast-curing characteristics is to solve the antinomy between fast cure and excellent flowability of materials. The work aims at balancing the relationship of fast cure and excellent flowability by adjusting the phenolic resin structure.Firstly, the effects of pH value, catalyst dosage, and the phenol/formaldehyde mole ratio on the stability of synthesis and resin properties are investigated. It is found that the key factor of reaction stability is the control over the methylol concentration. The form and ratio of ortho linkage to para linkage(hereinafter referred to as O/P ratio) of phenolic resins, which can be quantitatively measured by ~(13)C-NMR.The activation energy of curing reaction and the curing process of phenolic reisn with varying O/P ratio are studied by a nonisothermal differential scanning calorimetry (DSC). The activation energy decreases with increasing the O/P ratio, while a lower activation energy indicats that the reaction proceeds faster at a given temperature. Many microgels grow without restraints in the initial stage of curing. The growth rate increases with increasing the O/P ratio. As the reaction proceeds, the number of microgels increases, the particles are more densely distributed, the curing
process becomes diffusion-controlled, and there is little effect of the O/P ratio on the rate. The higher the curing temperature or the higher O/P ratio, the more constituents and the larger quantity of small molecules in the cured resin.In order to adjust the relationship of cure and flowability of phenolic resin fast curing injection molding materials, the effects of rolling conditions and O/P ratio on the material shaping time and flowability are studied. It is showed that the rolling temperature and time have evidently effects on the shaping time and flowability. The extent of flowability mainly depends on the O/P ratio. The higher the O/P ratio, the more obvious the tendency of flowability reduction. The shaping time is shortened with increasing the rolling temperature or time, but the O/P value has little effect on the shaping time. Under the optimized rolling conditions, the key factor on shaping time is the O/P ratio, the shaping time is shortened with increasing the O/P ratio, while the O/P value has little effect on the flowability of phenolic resin injection molding materials.The rheological behavior of phenolic resin injection molding materials is studied with brabender experiments. A rheological model based on the dual-Arrhenius equation is established and used to simulate the rheological behavior of the materials. The model predication is in a good agreement with experimental data. The injection-processing window of the materials can be well determined based on the developed model.The composites of magnesium hydroxide sulfate whisker and phenolic resin are prepared by an in-situ filling technique. Whiskers pre-treated with a coupling agent exhibit good dispersity. With TGA and DSC analysis, it is found that the phenolic resin has a better thermal stability at high temperatures and higher curing rates when a small amount of the pre-treated whisker is introduced by the in-situ filling technique. The flexural and impact strengths of the composite molding materials are also increased significally.A dynamic mechanical analysis (DMA) and a scanning electron microscope (SEM) are used to investigate the degree of resin curing and the state of glass fibers dispersion and wetting of the reinforced materials. The blend has more loosely
crosslinked structures and lower cure degrees than the pure resol or novolac. The glass fibers are dispersed and wetted better in the blend. The blend is therefore prepared to obtain the phenolic injection molding materials with improved impact and flexural strengths and heat-resistance.Viscoelastic characteristics of the cured glass fiber-reinforced phenolic materials are investigated through glass transition, postcured and degradation reaction processes at high temperatures up to 350 °C. A typical glass transition of the crosslinked thermoset polymer is followed by irreversible postcured and degradation reactions, which exhibit an increasing storage modulus. A postcured and degradation master curve is constructed using the vertical and horizontal shift factors, both of which comply well with the Arrhenius equation. Using an analogy to the standard linear solid (SLS) model, a viscoelastic modeling methodology is developed to characterize the temperature-dependent complex moduli of the glass fiber-reinforced phenolic materials. The calculated master curve and storage modulus of glass fiber-reinforced phenolic materials agree well with the experimental data.N-Phenyl maleimide-modified novolac resin is synthesized by a condensation polymerization of N-phenyl maleimide and formaldehyde with phenol slowly feed to a reactor in the present of an acid catalyst. The polymerization conditions are optimized to obtain a high reaction conversion of PMI and a proper viscosity of PPMF. It is found that the reaction competition and conversion ratio for PMI are enhanced with an increase in the feeding time of phenol. As the reaction reflux time is increased, the conversion of PMI and the viscosity of PPMF are increased. At higher reaction temperatures or more PMI, the conversion of PMI decreases. The resins are characterized by FTIR, BC-NMR and thermal analyses. It is found that the N-phenyl maleimide groups are combined into the chains of novolac. The N-phenyl maleimide content of PPMF around 33% can be reached. The DSC curves reveal two curing peaks. The one at 150°C is attributed to the condensation reaction of methylol group formed in a minor quantity on the phenyl rings. The other at around 250°C is attributable to the addition curing reaction of the maleimide groups. A TGA analysis shows that the cured PPMF has better thermal properties.
The effect of postcure on the properties of different cured phenolics is studied. The properties of cured phenolics after postcure, such as heat-resistance, mechanical properties, weight loss, water absorption, and electrical properties are measured. A DMA is used to investigate the effects of postcuring on phenolics materials. It is found that the storage modulus of the materials can be increased while the damping capacity decrease by the postcure, which yields an increase in crosslinking density. The results show that the improvement of mechanical and heat-resistant properties of moldings is due to an increase of crosslinking density and the interfacial bonds between the fibers and the resin matrix by the postcure. The results also show that the decrease of water absorption of moldings is due to the increase of hydrophobic nature of wood flour included in moldings by postcure. The reasons for the improvement of the electrical properties by postcure are also discussed.
酚醛注塑料的成型性能主要涉及固化性能和流动行为两个方面,制备快速成型酚醛注塑料的技术关键在于合理解决快速固化与流动特性之间的矛盾。论文通过调控酚醛树脂结构,研究树脂的固化行为及其注塑料制备与成型过程中的化学流变特性,优化了制备工艺,有效地平衡了注塑料的固化成型性与流动特性间的关系。
首先考察了酚醛缩合反应体系中pH值、催化剂及物料配比等因素对酚醛树脂结构的影响,探索了高邻位酚醛树脂合成过程中影响反应稳定性的关键因素。研究表明,采用复合催化剂可以调控树脂的结构,得到不同O/P值(酚醛树脂链结构中的邻对位比)的酚醛树脂;控制反应后期羟甲基的浓度,可以抑制支化反应,使反应稳定地进行;用~(13)C-NMR方法可定量地表征酚醛树脂的结构及其O/P值。
酚醛树脂的固化行为直接影响到其注塑料的成型与注塑制品的性能。本文分别采用DSC分析和抽提等方法研究了不同O/P值酚醛树脂的固化活化能及固化历程。发现酚醛树脂的固化活化能随着其O/P值的增加而降低,固化进程变得更加容易。在酚醛树脂的固化过程中,先形成大量微凝胶,形成微凝胶的速度随树脂O/P值的增加而加快;微凝胶继续相互碰撞挤压进一步形成固化网络结构,该过程为扩散控制,固化速度不受酚醛树脂O/P值的影响。提高固化温度或树脂的O/P值可有利于固化结构与组成的均一性。
为了调控快速成型酚醛注塑料的固化程度及平衡注塑料的成型与流动性之间的关系,考察了辊炼工艺、树脂O/P值对酚醛注塑料的成型时间及流动特性的影响。发现树脂O/P值愈高,其注塑料的流动性随辊压温度或辊压时间的增加而
Phenolic resins and phenolic injection molding materials belong to an important group of thermosetting polymers with very good fire resistance, dimensional stability, and excellent insulation properties. However, some key issues, such as structure and curing of phenolic resins and chemorheology of phenolic injection molding materials, and viscoelastic and postcured characteristics of phenolics still remain to be resolved. In this work, phenolic injection molding materials with fast-curing characteristics, phenolic injection molding materials with high mechanical and heat resistance properties, and the postcured properties of different phenolic resin materials reinforced with wood flour and glass fiber also investigated systematically.Injection properties of phenolic injection molding materials are related to curing and flowability. The key technical point in preparing phenolic injection molding materials with fast-curing characteristics is to solve the antinomy between fast cure and excellent flowability of materials. The work aims at balancing the relationship of fast cure and excellent flowability by adjusting the phenolic resin structure.Firstly, the effects of pH value, catalyst dosage, and the phenol/formaldehyde mole ratio on the stability of synthesis and resin properties are investigated. It is found that the key factor of reaction stability is the control over the methylol concentration. The form and ratio of ortho linkage to para linkage(hereinafter referred to as O/P ratio) of phenolic resins, which can be quantitatively measured by ~(13)C-NMR.The activation energy of curing reaction and the curing process of phenolic reisn with varying O/P ratio are studied by a nonisothermal differential scanning calorimetry (DSC). The activation energy decreases with increasing the O/P ratio, while a lower activation energy indicats that the reaction proceeds faster at a given temperature. Many microgels grow without restraints in the initial stage of curing. The growth rate increases with increasing the O/P ratio. As the reaction proceeds, the number of microgels increases, the particles are more densely distributed, the curing
process becomes diffusion-controlled, and there is little effect of the O/P ratio on the rate. The higher the curing temperature or the higher O/P ratio, the more constituents and the larger quantity of small molecules in the cured resin.In order to adjust the relationship of cure and flowability of phenolic resin fast curing injection molding materials, the effects of rolling conditions and O/P ratio on the material shaping time and flowability are studied. It is showed that the rolling temperature and time have evidently effects on the shaping time and flowability. The extent of flowability mainly depends on the O/P ratio. The higher the O/P ratio, the more obvious the tendency of flowability reduction. The shaping time is shortened with increasing the rolling temperature or time, but the O/P value has little effect on the shaping time. Under the optimized rolling conditions, the key factor on shaping time is the O/P ratio, the shaping time is shortened with increasing the O/P ratio, while the O/P value has little effect on the flowability of phenolic resin injection molding materials.The rheological behavior of phenolic resin injection molding materials is studied with brabender experiments. A rheological model based on the dual-Arrhenius equation is established and used to simulate the rheological behavior of the materials. The model predication is in a good agreement with experimental data. The injection-processing window of the materials can be well determined based on the developed model.The composites of magnesium hydroxide sulfate whisker and phenolic resin are prepared by an in-situ filling technique. Whiskers pre-treated with a coupling agent exhibit good dispersity. With TGA and DSC analysis, it is found that the phenolic resin has a better thermal stability at high temperatures and higher curing rates when a small amount of the pre-treated whisker is introduced by the in-situ filling technique. The flexural and impact strengths of the composite molding materials are also increased significally.A dynamic mechanical analysis (DMA) and a scanning electron microscope (SEM) are used to investigate the degree of resin curing and the state of glass fibers dispersion and wetting of the reinforced materials. The blend has more loosely
crosslinked structures and lower cure degrees than the pure resol or novolac. The glass fibers are dispersed and wetted better in the blend. The blend is therefore prepared to obtain the phenolic injection molding materials with improved impact and flexural strengths and heat-resistance.Viscoelastic characteristics of the cured glass fiber-reinforced phenolic materials are investigated through glass transition, postcured and degradation reaction processes at high temperatures up to 350 °C. A typical glass transition of the crosslinked thermoset polymer is followed by irreversible postcured and degradation reactions, which exhibit an increasing storage modulus. A postcured and degradation master curve is constructed using the vertical and horizontal shift factors, both of which comply well with the Arrhenius equation. Using an analogy to the standard linear solid (SLS) model, a viscoelastic modeling methodology is developed to characterize the temperature-dependent complex moduli of the glass fiber-reinforced phenolic materials. The calculated master curve and storage modulus of glass fiber-reinforced phenolic materials agree well with the experimental data.N-Phenyl maleimide-modified novolac resin is synthesized by a condensation polymerization of N-phenyl maleimide and formaldehyde with phenol slowly feed to a reactor in the present of an acid catalyst. The polymerization conditions are optimized to obtain a high reaction conversion of PMI and a proper viscosity of PPMF. It is found that the reaction competition and conversion ratio for PMI are enhanced with an increase in the feeding time of phenol. As the reaction reflux time is increased, the conversion of PMI and the viscosity of PPMF are increased. At higher reaction temperatures or more PMI, the conversion of PMI decreases. The resins are characterized by FTIR, BC-NMR and thermal analyses. It is found that the N-phenyl maleimide groups are combined into the chains of novolac. The N-phenyl maleimide content of PPMF around 33% can be reached. The DSC curves reveal two curing peaks. The one at 150°C is attributed to the condensation reaction of methylol group formed in a minor quantity on the phenyl rings. The other at around 250°C is attributable to the addition curing reaction of the maleimide groups. A TGA analysis shows that the cured PPMF has better thermal properties.
The effect of postcure on the properties of different cured phenolics is studied. The properties of cured phenolics after postcure, such as heat-resistance, mechanical properties, weight loss, water absorption, and electrical properties are measured. A DMA is used to investigate the effects of postcuring on phenolics materials. It is found that the storage modulus of the materials can be increased while the damping capacity decrease by the postcure, which yields an increase in crosslinking density. The results show that the improvement of mechanical and heat-resistant properties of moldings is due to an increase of crosslinking density and the interfacial bonds between the fibers and the resin matrix by the postcure. The results also show that the decrease of water absorption of moldings is due to the increase of hydrophobic nature of wood flour included in moldings by postcure. The reasons for the improvement of the electrical properties by postcure are also discussed.
引文
1 Matsumoto A., Study on modified phenolic resin. Ⅰ. Modification with homopolymer prepared from p-hydroxyphenylmaleimide, Journal of Applied Polymer Science, 1991(43): 365～372
2 Shengzu Wang, Sabit Adanur and Bor Z. Jang, Mechanical and thermo-mechanical failure mechanism analysis of fiber/filler reinforced phenolic matrix composites, Composites part B, 1997(28): 215～231
3 J. Wolfrum, G. W. Ehrenstein, Interdependence between the curing, Structure, and the mechanical properties of phenolic resins, Journal of Applied Polymer Science, 1999 (74): 3173～3185
4 Chen-Chi M. Ma, Chin-Tsung Lee, Hew-Der Wu, Mechanical properties, thermal stability, and flame retardance of pultruded fiber-reinforced poly (ethylene oxide)-toughened novolak-type phenolic resin, Journal of Applied Polymer Science, 1998 (69): 1129～1136
5 Keith C. Hong, Marco Ravasi, Nora Keil, Bruce Vigeant, Yunshang Ma, Effect of organic acids on the mechanical properties of phenolic resin composites, Journal of Applied Polymer Science, 2000 (76): 642～647
6 B. Redjel, Mechanical properties and fracture toughness of phenolic resin, Plastic, Rubber and composites Processing and Applications, 1995(24): 221～228
7 Tohru Morii, Asami Tanaka, Hiroyuki Hamada, Influence of molding condition on tensile properties of flat braided fabric reinforced phenolic composite, Composites: Part A, 2001 (32): 1505～1511
8 A. P. Mouritz and Z. Mathys, Mechanical Properties of Fire-damaged Glass-reinforced Phenolic Composites, Fire and Materials, 2000(24): 67～75
9 Feng-Yih Wang, Chen-Chi M. Ma, Wen-jia Wu, Mechanical Properties, Morphology, and Flame Retardance of Glass Fiber-Reinforced Polyamide-Toughened Novolac-Type phenolic resin, Journal of Applied Polymer Science, 1999 (73): 881～887
10 Renata Lubczak, Novel Phenol-Formaldehyde Resins, 1 Novolaks, Macromol. Mater. Eng., 2002(287): 619～626
11 林薇薇,丁力,硅酸铝纤维/酚醛树脂复合体系的研究,浙江大学学报,1995(4):459～464
12 Gupta, Phenolic molding materials and processes, US 4785040, 1988
13 Landi, Heat stable phenolic composition containing aramid fibers, US 4725650, 1988
14 Tamotsu Ishida, Eiji Funatsu, Process for injection molding of phenolic resin molding material, US 5679305, 1997
2 Shengzu Wang, Sabit Adanur and Bor Z. Jang, Mechanical and thermo-mechanical failure mechanism analysis of fiber/filler reinforced phenolic matrix composites, Composites part B, 1997(28): 215～231
3 J. Wolfrum, G. W. Ehrenstein, Interdependence between the curing, Structure, and the mechanical properties of phenolic resins, Journal of Applied Polymer Science, 1999 (74): 3173～3185
4 Chen-Chi M. Ma, Chin-Tsung Lee, Hew-Der Wu, Mechanical properties, thermal stability, and flame retardance of pultruded fiber-reinforced poly (ethylene oxide)-toughened novolak-type phenolic resin, Journal of Applied Polymer Science, 1998 (69): 1129～1136
5 Keith C. Hong, Marco Ravasi, Nora Keil, Bruce Vigeant, Yunshang Ma, Effect of organic acids on the mechanical properties of phenolic resin composites, Journal of Applied Polymer Science, 2000 (76): 642～647
6 B. Redjel, Mechanical properties and fracture toughness of phenolic resin, Plastic, Rubber and composites Processing and Applications, 1995(24): 221～228
7 Tohru Morii, Asami Tanaka, Hiroyuki Hamada, Influence of molding condition on tensile properties of flat braided fabric reinforced phenolic composite, Composites: Part A, 2001 (32): 1505～1511
8 A. P. Mouritz and Z. Mathys, Mechanical Properties of Fire-damaged Glass-reinforced Phenolic Composites, Fire and Materials, 2000(24): 67～75
9 Feng-Yih Wang, Chen-Chi M. Ma, Wen-jia Wu, Mechanical Properties, Morphology, and Flame Retardance of Glass Fiber-Reinforced Polyamide-Toughened Novolac-Type phenolic resin, Journal of Applied Polymer Science, 1999 (73): 881～887
10 Renata Lubczak, Novel Phenol-Formaldehyde Resins, 1 Novolaks, Macromol. Mater. Eng., 2002(287): 619～626
11 林薇薇,丁力,硅酸铝纤维/酚醛树脂复合体系的研究,浙江大学学报,1995(4):459～464
12 Gupta, Phenolic molding materials and processes, US 4785040, 1988
13 Landi, Heat stable phenolic composition containing aramid fibers, US 4725650, 1988
14 Tamotsu Ishida, Eiji Funatsu, Process for injection molding of phenolic resin molding material, US 5679305, 1997